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Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services (2004)

Chapter: 3 Current Meteorological and Transportation Activities Relevant to Road Weather

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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

3
Current Meteorological and Transportation Activities Relevant to Road Weather

Recent and anticipated research and technological advances position the field of road weather for significant steps forward in understanding and capability. Observational capabilities have made great strides, making it possible to obtain a progressively more comprehensive picture of current weather and roadway conditions in recent years. The transportation community is moving in the direction of a road network being operated as a “smart” adaptive system. Accompanying these and other advances in meteorology and transportation are improvements in communications, computational capabilities, and geographic information systems (GIS)—technologies that have clear applications to the road weather problem. In this chapter the committee highlights many current research and development activities that can be applied to road weather research, as well as other existing capabilities that have direct applications to road weather research but have not yet been fully exploited.

OBSERVING AND MODELING THE WEATHER

In Situ Meteorological Observations

Surface weather observations provide benchmark data about atmospheric and surface conditions to the scientific community and a broad spectrum of weather information users. The primary surface-weather-observing system in the United States is the Automated Surface Observing System (ASOS) that has been deployed over the past decade by the Federal Aviation Administration, Department of Defense, and National Oceanic and Atmospheric Administration (NOAA)/National Weather Service (NWS). There are nearly 1,000 ASOS sites across the United States; of those, 569 Federal Aviation Administration–sponsored and 313 NWS-sponsored sites

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

are located at airports throughout the country (http://www1.faa.gov/asos/asosinfo.htm). These data are important in the verification of weather forecasts, in providing real-time weather information to the aviation community, and as input into data assimilation systems for numerical weather prediction. None specifically target the roadway environment. The ASOS is a fully automated system that provides an extensive suite of meteorological observations without human observers. It is sufficiently sophisticated to provide both routine hourly reports and special observations as warranted by changing conditions. The basic data given in each report include sky condition (clouds to 12,000 feet), visibility, present weather, surface pressure, temperature, dewpoint temperature, wind, and liquid precipitation amount. Although not routinely used, the ASOS has the capability to report as often as every five minutes. It was designed to support NWS warning and forecast operations and Federal Aviation Administration aviation weather needs; in addition, the system supports hydrological and climatological programs.

Despite its value to many users, the ASOS does not meet all users’ requirements, largely because there are relatively few stations and because their observations are representative only of a small area near the site. As a result various user groups have developed and installed their own specialized surface-observing systems. Representativeness of surface observations is particularly important to the roadway environment, where minor differences in the physical environment (e.g., slope and exposure) lead to dramatically different effects. Although the ASOS provides useful data, it was never intended to be used to characterize the roadway environment; therefore, additional networks that target the roadway environment are needed.

Another very similar system is the Automated Weather Observing System (AWOS), which is a suite of sensors designed to collect and disseminate weather data primarily to assist the aviation community. The systems are classified as federal, which are owned and maintained by the Federal Aviation Administration, and nonfederal, which are owned and maintained by state, local, and private organizations. There are six different AWOS sensor arrays. The most basic array of sensors report wind speed (including gusts) and direction, temperature, dewpoint temperature, pressure, and density. The other five arrays build off this basic suite by reporting such additional parameters as visibility, sky condition, present weather, or lightning detection. Over 600 AWOS sites exist throughout the United States (http://www1.faa.gov/asos/awosinfo.htm). As with the ASOS, the AWOS was not deployed to observe the roadway environment, although its data are useful for synoptic weather observing and forecasting purposes.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

The need for high-density observations is not unique to highway operations. Numerous mesoscale observing networks have been deployed around the United States, including the Oklahoma Mesonet (Horel et al., 2002b) and the Atmospheric Radiation Measurement Cloud and Radiation Testbed site (Stokes and Schwartz, 1994) in the central Plains. MesoWest, a heterogeneous collection of over 70 networks providing more than 2,800 observations, was assembled over the western United States in part to support the 2002 Winter Olympics in Salt Lake City, Utah (Horel et al., 2002a, b). These, as well as other networks operated by federal, state, or local governments or private entities, have been installed to serve special needs: most often meteorological research, agricultural operations, or air quality monitoring.

In addition to the surface-based observations, in situ weather data are routinely collected on commercial aircraft as part of the Aircraft Communication Addressing and Reporting System (ACARS) (Moninger et al., 2003). This program is the largest and longest-running data collection effort developed specifically for constantly moving platforms; it provides 80,000 reports a day with critical information about temperature, humidity, and wind in the atmosphere up to 15 km altitude (Figure 3-1). A similar system for

FIGURE 3-1 Locations of observations obtained from aircraft and collected in the Aircraft Communication Addressing and Reporting System (ACARS) for a 3.5-hour period in March 2000. The data are color-coded to reflect the height where they were obtained. SOURCE: NOAA.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-2 Daily streamflow conditions for January 21, 2004. Black indicates a new record high for the day, blue indicates flow greater than the 90th percentile, light blue indicates flow between the 75th and 89th percentile, green indicates flow between the 25th and 74th percentile, orange indicates flow between the 10th and 24th percentile, dark red indicates flow less than the 10th percentile, and bright red indicates a new record low for the day. SOURCE: U.S. Geological Survey.

observing the roadway environment using vehicle probes is described in “Observing and Modeling the Roadway Environment” later in this chapter.

In addition to in situ sensors that monitor meteorological conditions, there are networks that monitor responses to those conditions. Of greatest concern to the roadway environment is heavy precipitation, which can lead to flash flooding. The U.S. Geological Survey operates a nationwide network of gauges to measure streamflow, data that are available in near realtime (Figure 3-2). These data can be used—as in Louisiana’s HydroWatch system (Wolshon and Levitan, 2002)—to gauge flood threat and if correlated with road elevation information, to determine when roads may become submerged.

Remote-Sensing Observations

Instruments that can observe atmospheric or land surface properties remotely offer ways to extend the spatial coverage of the observation net-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

work. These instruments can be “active,” in which case they send out a pulse of electromagnetic energy and then use the reflected signal to determine characteristics of the atmosphere, or they can be “passive,” in which case they measure radiation emitted naturally by the atmosphere.

Radar (Figure 3-3) is a widely used active remote-sensing technique that provides near real-time observations of the atmosphere under both clear-air and precipitating conditions. The deployment in the 1990s of Next Generation Weather Radar (NEXRAD) has provided the United States with a national remote-sensing network using Doppler radars (NRC, 2002). The radars provide nearly continuous monitoring of precipitating, severe weather complexes, and, when operating in clear-air mode, of nonmeteorological echoes (e.g., insects, dust), which can indicate wind speed and direction. NEXRAD incorporates sophisticated signal processing to sense the Doppler shift in the echoes returned from

FIGURE 3-3 A Doppler Radar. SOURCE: Bob Baron, Baron Services.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

moving scatterers, thereby providing information on the wind field in the observed region. A new “volume scan” of a three-dimensional region around each radar is available every five to six minutes.

Efforts are currently under way to (1) integrate other radars producing a weather signal (particularly those operated by the Federal Aviation Administration) in order to enhance coverage and provide redundancy; (2) upgrade the radar to improve its capabilities for sensing precipitation; and (3) make higher-resolution radar data and derived products more generally available. Additionally, dual-polarization radars (i.e., radars that transmit and receive both horizontal and vertical polarizations) have the potential to aid weather observation and prediction by distinguishing between rain and hail and by identifying the precipitation type in winter storms. These radars could be installed in the national radar network within 5 to 10 years. Also in development are high-resolution national composites or mosaics, which will merge all available radar data into one database for the nation. Current regulations prevent NEXRADs from being operated at beam elevations below 0.5°, limiting the extent to which the radar can see very low elevations. Despite this institutional limitation, the NEXRAD is able to track precipitation, determine winds, and detect other phenomena such as blowing dust; thus it has the potential to be applied effectively to improving road weather information products (Mahoney and Meyers, 2003).

Profilers are vertically pointing Doppler radars that collect temperature, moisture, or wind data through the atmosphere. For example, 400-MHz-band wind profilers are able to detect winds directly above the profiler site at heights from about 500 m to 16 km, making them useful for weather forecasting. Additionally, there are 900-MHz-band radar wind profilers that can be combined with Doppler sodars to obtain boundary layer winds down to about 30 m. When wind profilers are coupled with radio acoustic sounding systems (RASS), temperature profiles down to approximately 1 km also can be obtained. A sequence of wind profilers for Conway, Missouri, is shown in Figure 3-4. Though profilers are a reliable, proven technology, there is not a dense network of these observations, and the lack of data at lower levels and the coarse vertical resolution limit their usefulness for near-surface applications (NRC, 2003c). Figure 3-5 shows the location of wind profiler sites in the contiguous United States. Recent advances in wind profiler technology have created the capability to monitor the altitude of the melting level in winter storms.

Observations from instruments on satellite platforms that actively and passively sense visible, infrared, and microwave radiation now routinely provide data that can be processed for information on the distribution of

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-4 Hourly wind profiler observations over Conway, Missouri, on July 31, 2003. SOURCE: NOAA.

atmospheric and surface parameters in both the horizontal (imagers) and vertical (sounders). One widely used satellite observation is water vapor imagery from NOAA’s Geostationary Operational Environmental Satellite (GOES); such imagery often is animated to show the movement, development, and dissipation of large-scale weather systems. Satellite data provide excellent spatial coverage, filling in observations of weather conditions between surface-observing systems, and can be frequently updated. Civilian satellite sensor data are limited, however, in that they cannot resolve features the size of highways.

Several satellite-based sensing systems under development hold promise for applications to the roadway environment. Wind Index (WINDEX), an experimental GOES product, estimates the highest wind gusts that would occur if showers or thunderstorms were to develop. WINDEX is produced hourly from the sounder product and plotted on a satellite image. Originally developed for aviation operations, it could be used by surface transportation managers as an outlook to the potential occurrence of high wind and blowing dust associated with showers and thunderstorms, thus activating

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-5 Distribution of wind profiler and radio acoustic sounding systems (RASS) sites in the contiguous United States. The star represents a wind profiler coupled with a RASS; the circle represents a wind profiler only; and the triangle represents a RASS only. The symbol colors represent data availability which vary daily. SOURCE: NOAA’s Forecast Systems Laboratory.

cautions on dynamic message signs. On average, WINDEX estimates are within 5 knots of observed maximum surface wind gusts.

A fog and low cloud imaging capability, developed in support of aviation operations, analyzes different wavelengths of infrared radiation and using the differences, identifies low clouds and fog (Figure 3-6). Distinguishing between low clouds and fog is a challenging problem because there is a strong dependence on the underlying topography. Merging the satellite information with three-dimensional GIS data could lead to enhanced capabilities for distinguishing between low clouds and fog.

The Hydro-Estimator, one of the oldest quantitative derived satellite products, estimates precipitation down to the county level and, when combined with three-dimensional GIS data, could assist in anticipating prob-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-6 Fog location (a) and depth (b) over San Francisco Bay. SOURCE: NOAA.

lems in flash-flood-prone areas (Figure 3-7). These data are being incorporated in hydrological prediction models to forecast river and stream flows.

Monitoring the vast tropical oceans is a job that satellites do very well. GOES allows large regions of the tropical ocean to be continuously monitored throughout the life of a tropical cyclone, from genesis to dissipation. When in situ monitoring of tropical cyclones1 by aircraft, ocean buoys, or ship reports is not available, minimum pressure and maximum winds can be estimated in a variety of ways using remotely sensed data. Most commonly, tropical cyclone intensity is estimated from cloud patterns and temperatures using visible and infrared satellite imagery. Other instruments, such as the Advanced Microwave Sounding Unit, the Special Sensor Microwave/Imager, and scatterometers, are being used to estimate intensity and wind structure. GOES data provide frequent updates of track and intensity changes as the tropical cyclone moves toward land, contributing to substantial improvements in the forecast of land-falling tropical storms and hurricanes. A new product, the Tropical Rainfall Potential, utilizes both GOES

1  

“Tropical cyclone” is the generic term for all tropical low-pressure systems, including tropical depressions, tropical storms, and hurricanes. A tropical cyclone is named when it reaches tropical storm intensity (maximum sustained winds of 39–73 miles per hour), and it becomes a hurricane when reaching maximum sustained winds of 74 miles per hour or greater.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-7 Satellite and radar precipitation estimates from tropical storm Allison: (a) in situ observations from rain gauges and (b) satellite observations from the Hydro-Estimator. Each panel shows total rainfall in inches for the 24 hour period ending on June 6, 2001 at 12:00 UTC. SOURCE: National Aeronautics and Space Administration.

and microwave data from polar satellites as well as the storm track forecast to estimate the potential rainfall of a system when it makes landfall. Ideally, data from satellites, radars, and rain gauges should be combined to provide the best estimate of rainfall.

Geostationary and polar satellites can also provide other variables of potential relevance to the roadway environment. GOES sensors can monitor land temperature changes under clear sky conditions. Other sensors on recent satellite series (e.g., the Polar Orbiting Environmental Satellite, Earth Observation Satellites, Defense Meteorological Satellite Program) can monitor a variety of surface properties daily to weekly. For instance, the Normalized Difference Vegetation Index is used to monitor vegetation greenness and health; these data can be correlated with blowing dust, which limits visibility, and they could be important for modeling the moisture flux of the roadway environment. A variation of the satellite vegetation product uses current weather information, particularly precipitation and temperature data, in a new experimental fire risk product that might provide additional insights for roadway managers regarding the spread and impact a wildfire might have on surface transportation and evacuation operations. GOES near-infrared data can be used to monitor the fire locations as well as the coverage and changes in smoke plumes (Figure 3-8).

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-8 (a) Smoke from large fires in Montana and Idaho, August 22, 2000; (b) Narrow plumes from fires in Louisiana and Texas, September 5, 2000. SOURCE: National Aeronautics and Space Administration.

More than a hundred new sensors under development will be installed on satellite platforms within the next decade. Improved resolution, more frequent imaging, hyperspectral imaging, and new sounders are slated for launches by U.S. and global satellite partners. These sensors will provide new and improved observations of the atmosphere, including variables such as soil wetness, snow water equivalence, and smoke and aerosol detection over land. Examination of and development of applications from today’s satellite-based observations will prepare the surface transportation community to maximize the use of these data now and in the future.

Modeling the Atmosphere

Numerical weather prediction is the foundation of modern weather forecasting. Today’s state-of-the-science models are run multiple times per day and on horizontal grids with spacing as fine as just a few kilometers. The NWS currently is running the Eta model on a 12-km horizontal grid out to 3.5 days (84 hours) four times per day (http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/). Most forecast models are “full-physics” versions that provide explicit predictions of temperature, dewpoint temperature, wind, and precipitation. Forecasts for related sensible weather parameters, such as visibility and clouds, are generally derived by statistically post-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

processing the numerical model output, in some cases with direct human forecaster involvement.

Numerical weather prediction models have steadily improved since their inception (Figure 3-9). Accounting for this improvement are more accurate representations of subgrid-scale processes (e.g., clouds, precipitation, radiation), improved numerical methods including the ability to specify the initial conditions for the model using data assimilation, increased availability of observations, and increased power of supercomputers. When the accuracy of human-produced forecasts is assessed, it is noted that it tracks closely with the skill of the objective numerical weather prediction models, reflecting the strong dependence of human forecasters on the increased skill of numerical models (Figure 3-10). For the shorter-range forecasts extending out to three days, forecasters continue to add incrementally to the numerically generated forecasts using their knowledge and expertise.

The highest-resolution NWS models are currently run on horizontal grids on the order of 10 km, which limits resolvable features to those with horizontal dimensions greater than about 60 km. While this is sufficient to capture extratropical cyclones and the smoother characteristics of associ-

FIGURE 3-9 The skill score, an objective measure of the accuracy of numerical forecasts, of the National Centers for Environmental Prediction 500-hPa 36-hour forecast geopotential height has been tracked from the beginning of operational numerical weather prediction in 1955. A skill score of 100 is deemed perfect, where “perfect” means the average error is less than 20 percent. The complete history is presented in a review article by Kalnay et al. (1998). SOURCE: NRC (2000).

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-10 Relationship between the evolution of three- and five-day human and numerical forecasts. On average, the human forecasts are more skillful, but their improvement is strongly tied to improvements in numerical weather prediction forecasts. The score is the sea-level pressure anomaly correlation over North America, where the correlations are standardized to account for latitudinal dependence of the variability.

SOURCE: Kalnay et al. (1998).

ated fronts, it is not sufficient to capture, for example, phenomena on the scale of individual thunderstorms, fine-scale precipitation bands, or localized wind events, all of which are critical to surface transportation. As a result additional applications or approaches are necessary to downscale to the domain of the highway. Such applications include additional numerical models at finer resolutions, physical models, statistical post-processing, or human-produced forecasts.

Regional mesoscale numerical weather prediction models, with grid spacings down to a few kilometers and that are typically nested within a larger operational model, are currently being run by university researchers, private sector forecasting businesses, and local NWS partnerships. These efforts are proving themselves to be useful for highway maintenance decision making. For example, a Pacific Northwest consortium of weather users has pooled partner resources to develop and support a real-time mesoscale modeling program (Mass et al., 2003). The Washington State Department of Transportation is such a partner and utilizes the 4-km grid forecasts for a number of transportation applications. To date, these efforts have been rather ad hoc in where they have developed, generally being

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

driven by a combination of local interest, operational demand, and funding opportunities. Unfortunately, this approach leads to a lack of coverage, by any regional model, for some parts of the United States. Additional limitations include intermittent operations vulnerable to outages and uncertain funding.

The NWS is currently evaluating a new forecast presentation that involves a blending of numerical weather prediction forecasts, statistical and downscaling algorithms, and human forecaster decisions (Glahn and Ruth, 2003). The forecast is prepared using the Interactive Forecast Preparation System’s Graphical Forecast Editor. This software allows forecasters to manipulate and edit grids, which can be initialized directly from a variety of operational numerical weather prediction models. A variety of graphical, tabular, and text products can then be derived from the gridded information. The forecast is composed on a fine horizontal grid (less than or equal to 5 km), has temporal resolutions on the order of 1 hour for the first few days, and includes a full suite of forecast parameters. Smaller domain grids prepared at local forecast offices are combined to form a grid with complete national coverage and 5-km grid-point spacing called the National Digital Forecast Database. In addition to direct delivery to a number of weather-information users via the Web and other media, the system is being designed by the NWS to encourage private sector businesses and partners to extract weather forecast information for desired regions or domains. These could easily include highway transects and domains.

As computing resources improve, it becomes increasingly easy to run very fine spatial resolution mesoscale models on smaller and smaller computing platforms. While increased resolution has many benefits, it can present a mismatch between what is known about the initial state of the atmosphere and the resolution of the prediction. A skillful forecast requires good observations of the initial state of the atmosphere and surface boundary conditions, but most current atmospheric observation networks do not provide adequate spatial resolution of the initial conditions. An exception is the NEXRAD radar network, which has a resolution of a few hundred meters. Both experimental and quasi-operational models initialized with radar data have shown great skill in predicting the onset of thunderstorms, for example, on time scales of six or more hours. Work is currently under way to develop a national mesoscale model for both research and operations. Termed the Weather Research and Forecasting (WRF) model, this modeling system will likely use radar data as a primary high-resolution input. Additional data sets that are likely to provide value in high-resolution modeling include the ACARS, profiler, and satellite data.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

One way to deal with uncertainty in the initial conditions and derive useful forecast information is to use multiple, equally likely representations of the initial state. There are multiple techniques to obtain these initial state conditions, and each one is then used to initialize the numerical weather prediction model for multiple model realizations. This approach to determining a forecast, known as ensemble forecasting, provides useful information about the possible future evolution of the atmosphere in a probabilistic sense. Ensemble forecasting contrasts with the traditional method of taking the best available model and running it until it loses skill due to the growth of errors introduced in the initialization.

Ensemble forecasting approaches are successful in extending the period of forecast skill and also provide valuable probabilistic information on the likelihood of different conditions occurring. Figure 3-11 shows the probability of precipitation amounts exceeding certain thresholds. The precipita-

FIGURE 3-11 Ensemble-based probability of precipitation amounts exceeding thresholds of 0.1 inch, 0.25 inch, 0.5 inch, and 1 inch, September 18-19, 2003. SOURCE: NOAA

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

tion signature of hurricane Isabel can be seen along the mid-Atlantic coast. An American Meteorological Society (AMS) public statement “Enhancing Weather Information with Probability Forecasts” (http://www.ametsoc.org/AMS/policy/enhancingwxprob_final.html) was adopted by the AMS Council on January 13, 2002, and argues strongly for increased delivery of weather forecast information in probabilistic terms. This kind of information allows various user groups, including departments of transportation and transportation industries, to make cost-benefit decisions based on the likelihood of particular outcomes. These might include the threat of heavy snow, extreme cold, or critical thresholds of wind speed.

ROAD WEATHER FORECASTS

Operators and maintainers of roadways need specific, customized weather and road condition information in order to make the best operational planning decisions to provide a safe, efficient roadway system for users. Observed and forecast data needed most include temperature (pavement surface, air, dewpoint temperature), atmospheric conditions (cloud cover, visibility, and precipitation including probability, type, start and stop times, and amount including snow accumulation), and wind speed and direction. Ideally this information would be disseminated by common media (e.g., radio, cell phones) or displayed concisely in one integrated software interface that is easily interpretable.

Significant challenges remain in producing forecasts with spatial resolution on the scale of the roadway, but some efforts are already under way to provide targeted road weather forecasts for drivers and roadway maintenance workers. There are a few areas of the country where road weather forecasts are made available to the driving public. One such effort is being coordinated by the Washington State Department of Transportation in coordination with the Northwest Regional Modeling Consortium. The department joined the consortium, which has established meteorological realtime observing networks and modeling capabilities over the past 10 years, and added data from its own Environmental Sensor Stations (ESS) resulting in over 450 sites from which in situ meteorological data are gathered. These data, coupled with weather forecasts, are disseminated to provide real-time and forecast weather and road condition information to drivers and state maintenance crews with the objectives of helping drivers make better pretrip and en route decisions and providing roadway maintainers valuable information about the operability of the roadways. A pavement prediction model integrated with a land surface model also is available to provide current and

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

forecast pavement temperatures to assist road crews with anti-icing decisions and operations. A single Web site (http://www.wsdot.wa.gov/Rweather/) provides these weather and model data as well as traffic incident and construction information, highway surveillance cameras, and highway advisory radio messages.

Another major effort supported by the Federal Highway Administration (FHWA) is the development of the Maintenance Decision Support System, a prototype tool for providing decision support to winter road maintenance managers. The prototype is being developed cooperatively by six national labs, which the FHWA selected according to their expertise and tools that could be applied to the problem. Based on the declared needs of the winter maintenance community, the Maintenance Decision Support System was designed to be an easily usable, single-platform decision support tool for displaying comprehensive information and providing recommended courses of action as well as the anticipated consequences of action or inaction. The system uses existing road and weather data sources and augments them as necessary to produce diagnostic and prognostic maps of road conditions with emphasis on the 1- to 48-hour timeframe. This timeframe is defined by the maintenance community’s monitoring of incoming storms beginning approximately 48 hours before the event beginning, their activation of staff approximately 15 hours before, and their management (i.e., reassessment, coordination, and mitigation activities) approximately 1 to 3 hours before. During the winter of 2002–2003 the Maintenance Decision Support System prototype was deployed for field demonstration. Although only a few winter storms occurred, sufficient data were available to exercise the system. Field personnel responsible for winter maintenance operations felt that forecast accuracy must be improved before the system would be useful in improving the efficiency and effectiveness of winter maintenance control operations. Another, more comprehensive field demonstration is ongoing for the winter of 2003–2004.

Another project being supported by the FHWA with additional state departments of transportation, private, and international collaboration is FORETELL (http://www.foretell.com), an advanced weather prediction system that is being developed with the goals of reducing winter-related accidents and creating a viable road and weather information network. This Internet-accessible system acquires weather, agricultural, and road weather data to provide 10-km gridded 24-hour forecasts and nowcasts mapped to interstates and U.S. and state highways four times each day. FORETELL also uses advanced temperature models to calculate road surface temperature and predict future road conditions. After three seasons of test and evalua-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

tion, most elements of the program are working well, but forecast accuracy needs some improvement to be able to meet the high expectations of users.

In addition to the previously mentioned collaborations, the private sector also has been instrumental in leading the development of road weather forecast products. For example, the Advanced Transportation Weather Information System developed by Meridian Environmental Technology, Inc. was designed to provide decision support in planning and managing road construction and maintenance activities. The system includes multiple products, providing (1) site-specific weather and road forecast information for selected highways; (2) 36- to 48-hour area-specific forecasts; (3) current and forecast road restriction recommendations (e.g., to increase pavement life) based on freezing and thawing indexes combined with soil moisture data; and (4) a five-day site-specific, hour-by-hour weather forecast. Perhaps the most commonly used product is #SAFE, a phone system that served as a basis for the 511 system (described later), which drivers can call to learn about current and forecast road conditions along their corridor of travel. More information about these products can be found at http://www.meridian-enviro.com/products/trans.html.

Communicating Weather Information to Drivers

A variety of methods are available for communicating weather information to drivers. These include television, radio, and Web sites used to communicate weather information more generally, as well as mechanisms currently being developed to deliver targeted road weather information through Web sites, satellite radio, and the telephone, among others. Weather and traffic reports on television and radio are familiar to most. These reports typically provide current conditions and forecasts for metropolitan areas and substate regions, corresponding to their audience. Some television and radio stations have begun to take advantage of pavement sensor and weather data from ESS. These observations specific to the roadway might be displayed separately, rolled into an overall analysis of driving conditions, or used to make predictions, for example, when the pavement temperatures are well above freezing, that the road will not freeze for the next few hours even though snow is falling.

Most states have developed road weather Web sites that display realtime ESS (Box 3-1), ASOS, and other relevant data, including pavement temperature, air temperature, wind direction and speed, dewpoint temperature, precipitation, pavement condition, and subsurface temperatures (Figure 3-12). These Web sites may also show real-time cameras that monitor

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-12 Example of a map from the Iowa Winter Road Conditions Web site (http://www.iowaroadconditions.org). SOURCE: Iowa State Patrol.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

weather and traffic. Some of these Web sites are displayed in interstate highway rest areas.

In July 2000 the Federal Communications Commission designated 511 as a single national traveler information telephone number to be implemented by states and local jurisdictions. It is estimated that 511 will replace and consolidate nearly 300 travel information telephone numbers around the country. Great progress has been made in implementing this system, with most states supporting some level of activity (Figure 3-13). In snowbelt states where 511 is operational, the highest call volumes occur during the winter months when travelers use the service to receive road condition information. Ideally the system will be updated frequently so that near-realtime data will be reported. Many states are developing systems that allow users to interact with the system using voice recognition, which is a particularly important feature for cell phone users calling from the road.

Dynamic message signs are another important way to communicate to drivers (Figure 3-14). These signs have been in general practice for many

FIGURE 3-13 511 deployment status as of December 11, 2003. SOURCE: Resource 511.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-14 A dynamic message sign. SOURCE: Delaware Department of Transportation.

years, and they use a number of permanent and portable technologies such as reflective flip-disk, light-emitting diode, and fiber optics. Drivers tend to pay close attention to these signs because they are displayed so close to traffic and have changing messages; however, it is not known how well drivers respond to such signs. Only a limited amount of information can be placed on the signs. Care must be taken to ensure that the optimum information is conveyed, at the right place, and with the end of a hazardous stretch of road signed as well. In some places, the signs advise motorists to dial 511 or tune into Highway Advisory Radio, a traffic information dissemination tool widely used by traffic managers, construction crews, and roadway maintenance personnel. Only limited use has been made of dynamic message signs to alert drivers of poor weather conditions, even though the signs are an attractive communication mechanism because drivers do not need to take any special information retrieval action. Although Highway Advisory Radio often has a limited broadcast range and poor sound quality, its appeal is its immediate and simple accessibility. Nearly every vehicle has access to AM and FM radio, so it is immediately available to the average driver who does not invest in new, specialized technologies.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

Special Communication Needs and Tools for Motor Carriers

Roadway information services generally have been developed to most effectively meet the needs of the general motoring public. These services are sometimes limited to peak commuting times and travel routes, with information geared toward passenger car drivers in and around metropolitan areas. Trucking companies benefit from this information, but these commercial operators differ from the general motoring public in several ways, thus they require more specialized information to fully meet their operational and safety needs. Motor carriers operate 24 hours a day and 7 days a week; their trips often cover wide geographic areas comprising both metropolitan and rural areas. Routing and trip decisions usually are determined by a motor carrier’s dispatch center, often in advance of trips and according to tight pickup and delivery schedules. Commercial drivers generally have less flexibility in certain aspects of their travel decisions (e.g., arrival time) than passenger vehicle drivers.

Motor carriers currently access roadway information through several channels. Dispatchers regularly poll information sources to determine whether trucks are heading into severe conditions. They then communicate with the drivers over citizens band (CB) radio or cell phone and route them around the problem. Drivers frequently use CBs to get information from other drivers, but do not rely on this information alone due to the large amount of erroneous information circulating the airwaves. Drivers also rely on the 511 system because the single number makes it easy to access information as they travel across state lines. A major concern for motor carriers and their drivers is the level of potential distraction of drivers while they are on the road; therefore, delivery of information into a truck cab should be as unobtrusive as possible. Drivers usually review the dispatch messages when they stop their vehicles. Dispatch centers prefer exception-based information; that is, information that falls outside normal operational expectations. Dispatchers are extremely busy and do not want to be distracted by information that does not directly require their attention.

An objective for improving communication in the trucking industry is the complete integration of roadway and weather information into a dispatcher’s routing and dispatching software. This would allow all the information to be displayed in the dispatcher’s daily work environment, thereby minimizing effort to retrieve and use it. Such an integrated system should include graphical maps showing color-coded trouble areas and comprehensive information in a one-stop format for the carrier’s operating region.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

More accurate information about traffic and weather conditions would have many benefits for the trucking industry. With accurate estimated arrival times, trucking companies could better coordinate pickup and delivery schedules to minimize wait time. When a truck is running behind schedule or is expected to face a weather delay, the dispatcher could call ahead and reschedule the pickup or delivery for more efficient loading or unloading of the truck. Customers could be informed when a shipment is expected to be delayed due to roadway conditions. With accurate real-time information and predictive capabilities, dispatchers could more accurately determine whether additional loads or stops were feasible, taking hours-of-service constraints and roadway conditions into consideration. Dispatchers and managers could use roadway information to verify whether drivers are unable to meet their schedules due to adverse road conditions.

OBSERVING AND MODELING THE ROADWAY ENVIRONMENT

Observing the Roadway Environment

In many areas multiple sensors have been installed to monitor critical roadway conditions. These sensors measure atmospheric, pavement, and water level conditions, and they are collectively referred to as Environmental Sensor Stations (ESS) (Figure 3-15). The complement of sensors can include a subsurface temperature probe, a surface sensor, a precipitation and visibility monitoring system, and atmospheric sensors that measure wind speed and direction, temperature, and relative humidity. Surface sensors, such as the one shown in Figure 3-16, can provide information on water coverage, snow, black ice, temperature, and even the amount of chemical present in a slurry on the pavement surface. There are over 2,000 ESS owned by state transportation agencies; over 1,400 are field components of Road Weather Information Systems (RWIS), which typically are used to support winter road maintenance activities. Field data from ESS are collected and processed by RWIS collection centers, where modeling and dissemination services are furnished to automated warning centers, traffic operations, emergency managers, and road maintenance facilities for decision support. Careful monitoring of the roadway is an important element of intelligent transportation systems (ITS), described in more detail later in this chapter.

Vehicle detection is an important observational component for modern traffic control systems. The most common technology used for vehicle detection utilizes inductive loop detectors installed in the roadway subsurface,

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-15 Environmental Sensor Station. SOURCE: Curt Pape, Minnesota Department of Transportation.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-16 Pavement sensor. SOURCE: Jerry Waldman, Surface Systems, Inc.

which report the presence of a vehicle. Several newer technologies for vehicle detection allow for direct measurement of additional traffic parameters including traffic density, travel time, and vehicle turning movement. Most of these new technologies observe traffic remotely; for example, microwave Doppler radar can be used to observe vehicle speeds, passive infrared and acoustic detectors can determine vehicle presence or passage, and active laser radars can report vehicle passage, presence, and speed (Mimbela and Klein, 2000).

Video detection (Figure 3-17) of traffic and road conditions has become popular recently. With sophisticated image processing algorithms, informa-

FIGURE 3-17 Visual detector. SOURCE: Joseph Perrin, University of Utah.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

tion about vehicle passage, presence, speed, length, and lane change movement can be obtained from video (Mimbela and Klein, 2000). Video data can also be presented on weather or traffic Web sites so that drivers and roadway maintainers can check road conditions. Additionally, video data have great potential for providing weather information, particularly visibility, presence of fog, and precipitation type. Algorithms to automate retrieval of weather information from video data are currently being developed (Hallowell, 2003).

Challenges abound in operating and maintaining road weather observation networks as well as in collecting and quality controlling the data. Currently there are no international or U.S. national standards for the basic ESS suite of sensors, nor for the siting, operating range, accuracy, survivability, calibration, and maintenance of these systems. Development of standards is being considered, but they are not yet mandated. However, communication standards for RWIS are being developed to exchange data between RWIS and other sensors and to communicate weather and road conditions to end users (FHWA, 2002). A more detailed description can be found in the section below on intelligent transportation systems.

In situ collection of road characteristics and environmental conditions by instruments on moving vehicles could evolve into a system similar to the ACARS system that collects weather observations on aircraft. Vehicle probes are available that can collect information on (1) roadway conditions, such as surface temperature, subsurface temperature, moisture, chemical concentration, and surface condition; and (2) roadway characteristics, such as the friction coefficient and road geometry. They also provide another source for in situ meteorological data, including air temperature and dewpoint temperature, wind speed and direction, precipitation, and visibility. With their inclusion in the National ITS Architecture, the exploitation of vehicle probes as opportunistic data sources is likely to increase. As exciting as this is, research is needed to determine how best to handle the millions of observations obtained, including who will organize and process the data, how it can usefully be incorporated into models and disseminated to users, and whether the most critical elements are being observed.

Modeling the Roadway Environment

Most current efforts to model the roadway weather environment use idealized energy balance models to predict pavement temperature. Energy balance models include weather information, heat and moisture exchange between the surface and the atmosphere, and the effects of precipitation,

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

melting, freezing, and human activities (e.g., snow removal, application of salts to prevent freezing, and the traffic flow itself). The equation that describes the balance between sources and sinks of energy is

Rnet= H + LE + G + Qmelting + Qprecip+runoff + Qanthro

where Rnet includes the downwelling radiation from the Sun and atmosphere, the reflected solar radiation, and the upwelling infrared radiation from the surface; H and LE represent heat loss from the road to the atmosphere by convection and evaporation, respectively; G represents warming or cooling of the road; and the source/sink terms Q account for the effects of melting, precipitation and runoff, and human modifications to the surface. Qanthro includes heat originating from vehicles or the urban environment, or in the case of road construction, the heat released as the concrete or asphalt sets. Anthropogenic effects can also be included by modifying the other terms in the equation. Surface temperature can be determined by using an application of this equation. To estimate road slickness from frost or snow, one would combine a water-budget approach with temperature prediction that includes water phase changes and runoff.

Energy balance models have been used to predict road surface temperature since the 1980s when the U.K. Meteorological Office first used an energy balance model to predict the surface temperature of a dry road (Rayer, 1987). Such models have since become increasingly sophisticated and include the effects of water, ice, and traffic (e.g., Crevier and Delage, 2001; Jacobs and Raatz, 1996; Prusa et al., 2002; and Sass, 1992). Some of the complexities that can significantly affect road temperature are summarized in Table 3-1. An important limitation of energy balance models is their one-dimensionality; they are thus completely accurate only when surface conditions are horizontally homogeneous.

Energy balance approaches deal with energy exchange across the ground surface. Several approaches have been developed for roads in deep ravines, on steep hillsides, surrounded by high trees, and in other types of complex environments. Some researchers have approached this problem by solving the full three-dimensional energy balance for an area, as illustrated in Figure 3-18. These models tend to be computationally expensive and require substantial input data that are not readily available, and so they have not been widely applied.

Alternative approaches have been developed to investigate the complex roadway environment in models to predict surface temperature. Identifying scenarios and developing semi-empirical relationships or expert sys-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

TABLE 3-1 Factors Affecting Pavement Temperature

Factor

Effect

Shading by road banks, vegetation, and bridges

Cools pavement during the day

Radiative heating in the infrared in steep terrain, from trees, etc.

Reduces radiative cooling at night relative to what is expected for well-exposed places

Thickness of pavement

Changes heat transfer into the ground and evaporation rates

Pavement composition

Changes heat transfer into the ground and evaporation rates

Pavement structure

Changes heat transfer into ground, evaporation rates, and runoff patterns

Structure and moisture of roadbed and ground beneath

Changes heat transfer into the ground

Traffic

Mixes air near the road; frictional production of heat from tires “grabbing” the road; radiative exchange between road surface and vehicle; heat and moisture fluxes from exhaust gases; air conditioning, etc.

Bridges

Vents beneath as well as above leads to more surface area to exchange heat with environment; cooler at night; variety of construction materials involved

Urban environment

Input of energy by city, known as the “heat island” effect; structures affect mixing and hence fluxes at surface

Clouds and fog

Affect radiative transfer (cooler during day, warmer during night)

Precipitation on the road

Phase changes affect heat exchange; creates additional interface

Road treatment strategies

Reduces snow cover, leads to melting, or prevents ice from forming

Road contaminants

Creates additional interface; affects heat exchange; affects precipitation on road

tems to predict hazardous road conditions have been useful. For example, Eriksson (2001) identified combinations of synoptic conditions and roadway sheltering by trees and high banks that lead to slippery roads, and Postgard (2001) developed a set of empirical relationships between changes in weather conditions and road surface temperature. Takle (1990) developed an expert system to predict roadway frost 20 hours in advance based on temperature, cloud cover, forecast early-morning dewpoint temperature, precipitation, and wind speed and direction. Although such approaches may not be universally applicable, they work well in particular regions.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-18 (a) Map of land type and elevation over the study area near where I-90 crosses from Idaho into Montana. These data are used as input to the three-dimensional energy-balance calculation. (b) Calculated land surface temperatures over the study area. (c) Road surface temperature and wind speed along the roadway as presented to the user community. SOURCE: Edward Adams, Montana State University.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

ROADWAY OPERATIONS

Maintenance Management

To date, weather-related roadway maintenance activities have focused on responding to winter weather. The informational needs to support winter maintenance are fairly well defined (Figure 3-19). Snowplow operators, for example, need information that will allow them to determine the correct amount of chemical or abrasive to apply to the roadway. This decision depends on road surface conditions (e.g., temperature, chemical levels, and precipitation) during a 2- to 4-hour window, the typical time for a maintenance route. Inaccuracies in forecasts and the sensors that measure roadway conditions result in over- and misapplication of chemicals and abrasives, which adversely affects both budgets and the environment. Maintenance area supervisors, on the other hand, need to know the storm start time, the precipitation type and intensity, the storm ending time, road

FIGURE 3-19 Winter storm treatment life cycle. SOURCE: Robert Hallowell, MIT Lincoln Laboratory.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

surface temperatures throughout, and the weather conditions following the storm. Accurate storm forecasts are needed 18 hours ahead of the storm for the purpose of assigning shifts and mustering additional resources.

Current efforts build on the foundation laid in the early 1990s by the Strategic Highway Research Program (TRB, 2001a) and the Winter Maintenance International Scanning Tours conducted in 1994, 1998, and 2002. The highway operations section of the program contained a unit focused on winter operations research. The scanning tours created opportunities for exchanging snow and ice control technology and best practices with European countries and northern regions of Japan. These efforts have moved snow and ice control from being reactive, initiating operations only after the snow or ice begin to form, to proactive, beginning operations before the storm to prevent the bonding of ice or snow pack to the pavement. As implementation of the research results progressed, it became apparent that improvements in training, decision support, and equipment would be necessary to optimize the value of the research. This led to the pursuit of three ongoing activities:

  1. innovative interactive training on Road Weather Information Systems and Anti-Icing led by the American Association of State Highway and Transportation Officials (AASHTO),

  2. development and evaluation of the Maintenance Decision Support System led by the FHWA’s Road Weather Management Program (described in the “Road Weather Forecasts” section earlier in this chapter), and

  3. development and evaluation of the next-generation snow and ice control equipment led by a consortium of state departments of transportation.

With the introduction of new methods and technologies, winter maintenance managers and supervisors needed a better understanding of weather forecasting, snow and ice control chemicals, effective brine-making techniques, optimal application rates, dilution caused by weather and traffic, and pavement temperatures. Individual state agencies developed ad hoc training, but reductions in roadway maintenance staffs and the increased use of contractors resulted in a less experienced and smaller workforce. To meet these training needs AASHTO developed a computer-based, interactive, Road Weather Information System and Anti-Icing training program. Over 90 percent of the snowbelt states intend to use this training program, which will facilitate similar approaches to snow and ice control by their maintenance operators.

The correct snow and ice control equipment performing the right op-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

erations is needed to optimize winter maintenance operations. A consortium of snowbelt states led by the Iowa Department of Transportation has developed and field tested a new generation of snowplow truck. This truck is outfitted with off-the-shelf technology that uses real-time geolocated measurements of road temperature, surface chemistry, and surface friction, along with the ability to customize chemical application rates to predicted road conditions. This information is displayed for the plow operator and the supervisor so that both can monitor real-time operations. These automated features let the operator concentrate on driving the truck and allow the supervisor to monitor the entire fleet.

Traffic Management

Traffic management is the effort of roadway managers to optimize the efficiency and capacity of the roadway network. Over the past six decades the roadway system in the United States has expanded significantly, beginning with a U.S. highway system, followed by an interstate highway system and interconnecting arterials in metropolitan areas. The general public and commercial vehicle operators responded with ever-increasing traffic volume. New highway construction has now decreased markedly, yet the demand for roadway capacity continues to increase. The challenge to roadway operators is to manage the existing infrastructure with ever-increasing efficiency to produce a system that is safe with decreasing congestion and delays. Weather information is needed to improve roadway efficiency and capacity (Goodwin and Pisano, 2002).

Travel time, reliability, and delay are critical measures for system performance, both in real time and in archived applications. Traffic delay is being scrutinized in more detail to ascertain underlying causes. Weather is one of those causes as shown in Figure 3-20.

Traffic managers monitor roadway conditions and traffic incidents from traffic management centers. They use weather observations and forecasts from the commercial sector, including the media, to execute control strategies to manage traffic flow and advisory strategies to disseminate road weather information (Pisano et al., 2002). One control technique being employed in a few locations is the management of traffic signals when adverse weather is present or forecast (Perrin et al., 2001). When heavy rain, snow, slush, or icy conditions occur, operators access a traffic signal control system and manually implement longer-cycle signal-timing plans. Operators can further lengthen these cycles during peak commuting periods or worsening weather conditions. This technique reduces speeds and mini-

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-20 Causes of nonrecurring traffic delay. SOURCE: John Wolf, California Department of Transportation.

mizes the average number of stops per vehicle, thereby improving the safety and efficiency of the roadways. Once the road weather conditions improve, traffic signal operations are restored to normal.

Other control strategies used by traffic managers during inclement weather include speed management, land or vehicle restrictions, and guidance techniques (Pisano et al., 2002). Driver speed is managed based on the visibility, pavement, and traffic conditions by reducing speed limits to a safer velocity that is conveyed to drivers via dynamic message signs or variable speed limit signs. Traffic managers may also restrict access to road segments, lanes, or bridges or restrict the type of vehicles (e.g., tractor-trailers, vehicles without tire chains) allowed on portions of the roadway when visibility is low or lanes are obstructed due to snow or flooding. Finally, when visibility is poor, traffic managers may use pavement lights embedded in the road surface to delineate travel lanes, or they may use patrol vehicles with flashing lights to lead drivers safely through affected areas.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

Although these traffic management tactics can greatly improve driver safety during inclement weather or poor road conditions, they are reactive rather than proactive. Better system performance relies on deployment of transportation management systems that account for weather (Nelson, 2002). Most authorities are quite familiar with the range of weather events that can affect their roadways, but only some organizations have mitigation strategies in place to exploit the use of advanced weather information.

Emergency Management

Major advances in intelligent transportation systems, weather research, vehicle technologies, electronics, and geographic information systems have created tremendous opportunities for improved emergency management practices for the transportation industry. Although emergency response to weather disasters such as tornadoes has been studied to some extent (Goodwin, 2003a), responding to tropical cyclones has received the most attention from the surface transportation research community because they call for massive evacuations relying primarily on highways. Efforts to address surface transportation implications of other weather-related emergencies are less developed and are not discussed in detail here.

The intensity of tropical cyclones and the damage they inflict when making landfall create considerable transportation-related problems (Figure 3-21). From the 1970s through the early 1990s hurricane activity was moderate in the Atlantic basin (Gray et al., 1993), and there was a concurrent explosion in population along the Gulf and East Coast regions of the United States (Pielke and Landsea, 1998). The rapidly growing coastal population and increased tropical cyclone activity necessitated thorough, efficient evacuation plans. The United States is among a small number of countries that rely on mass evacuations to protect their population during hurricanes. Evacuations used to be the responsibility of emergency management and law enforcement officials, but after the major traffic jams associated with Hurricane Georges in 1998 and Hurricane Floyd in 1999, the professional transportation community took a more active role in the planning, management, and operation of evacuations (Wolshon et al., 2001). These two hurricanes highlighted the need for better planning and coordination, increased evacuation route capacity, and better information exchange.

The most important aspects of effective hurricane evacuations are advance warning times and access to transportation; this is especially important because the majority of deaths associated with hurricanes result from inland flooding, and drivers are particularly susceptible. Track and intensity

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-21 Flooding during Hurricane Floyd, September, 1999. SOURCE: Louisiana State University Hurricane Center.

forecasts from the NOAA/NWS National Hurricane Center are used to monitor a hurricane and determine if evacuation is necessary. This decision usually is based on the hurricane’s intensity (Table 3-2), size, track, and speed. A hurricane technically makes landfall when its eyewall—the most intense region of the storm—reaches land, but tropical storm- or hurricaneforce winds can occur much earlier when strong outer rainbands reach land. Timing is of the essence when allowing for configuration of all traffic control elements on evacuation routes, the actual evacuation process, clearing of all routes, and removal of evacuation-coordination personnel once deteriorating conditions commence. According to Wolshon et al. (2001), medium-size cities need at least 12 hours to initiate and complete evacuation, but larger cities with limited evacuation routes, such as New Orleans, may require up to 72 hours. The preferred minimum evacuation-advance-notification times of several coastal states is given in Table 3-3. Although initiating evacuation earlier gives more time for people to leave, it also gives more time for the track of a hurricane to change; the average 24-hour track error during 1992–2001 was 93 miles (Franklin et al., 2003).

Several technologies and procedures have been explored and, to some extent, adopted to improve the efficiency of evacuation procedures. One issue that often has been overlooked is the interference of work zones and

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

TABLE 3-2 The Saffir-Simpson Hurricane Scale, which Rates a Hurricane Based on Its Maximum Sustained Winds

Category

Winds (mph)

Effects

1

74-95

No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some coastal road flooding and minor pier damage.

2

96-110

Some roofing material, door, and window damage to buildings. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood 2 to 4 hours before arrival of center. Small craft in unprotected anchorages break moorings.

3

111-130

Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures, with larger structures damaged by floating debris. Terrain continuously lower than 5 feet above sea level may be flooded inland 8 miles or more.

4

131-155

More extensive curtainwall failures with some complete roof structure failure on small residences. Major erosion of beaches. Major damage to lower floors of structures near the shore. Terrain continuously lower than 10 feet above sea level may be flooded, requiring massive evacuation of residential areas inland as far as 6 miles.

5

> 155

Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5 to 10 miles of the shoreline may be required.

 

SOURCE: http://www.aoml.noaa.gov/general/lib/laescae.html.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

TABLE 3-3 Preferred Minimum Evacuation-Advance-Notification Times (in hours) for Several Southern and Eastern Coast States

 

Hurricane Category

State

1

2

3

4

5

Massachusetts

9

9

12

12

1

Rhode Island

12-24

12-24

12-24

12-24

12-24

Maryland

20

20

20

20

20

Virginia

12

18

24

27

27

South Carolina

24

24

32

32

32

Georgia

24-36

24-36

24-36

24-36

24-36

Mississippi

12

24

24

48

48

Louisiana

24

48

72

72

72

 

SOURCE: Wolshon et al., 2001.

the congestion caused by lane closures or detours. Most construction occurs during the summer, coinciding with the Atlantic tropical cyclone season, which extends from June 1 through November 30. To minimize this problem, some departments of transportation have included special provisions in construction contracts that require contractors to cease activities, clear their equipment, and reopen lanes in the event of an evacuation. Other states simply do not allow construction that reduces normal traffic capacity.

ITS information is being used increasingly during evacuations to collect and disseminate real-time data about traffic flow rates, road closures, weather conditions, and availability of alternate routes. Traffic cameras can be used to give visual confirmation of evacuation conditions. Highway advisory radio and dynamic messaging signs are being used to communicate important information to evacuees in a timely manner. Such information may include shelter locations, alternate evacuation routes, congestion and accident information, and services such as lodging and rest areas. The main limitation of such systems is that they most often exist in urban areas, whereas the majority of evacuation routes are in rural regions (Wolshon et al., 2001).

Since the traffic jams caused by hurricanes Georges and Floyd in 1998 and 1999, respectively, an evacuation procedure called “contraflow,” which reverses one or more lanes of traffic flow to increase capacity, has been explored (Figure 3-22). There are four variants to this contraflow technique, assuming two inbound and two outbound lanes divided by a median (e.g., an interstate, a four-lane divided highway): (1) all lanes reversed; (2) one

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-22 Contraflow along I-26 near Charleston, South Carolina, during reentry after Hurricane Floyd in September 1999. SOURCE: South Carolina Department of Transportation.

lane reversed and one lane with inbound flow for emergency service; (3) one lane reversed and one lane for normal inbound flow; and (4) one lane reversed and the use of left shoulder of outbound lanes. The reversal of all lanes increases capacity by about 70 percent. Reversing just one lane and leaving the other for either emergency or regular inbound flow increases capacity by 30 percent, but it also increases the potential for accidents. Usage of the left shoulder for extra outbound traffic improves capacity by only 8 percent, and it has the potential for the greatest problems due to lack of pavement suitable for driving and the inconsistency of shoulder widths (Wolshon et al., 2001).

There currently are no standards or guidelines for designing contraflow operations. Typically a median is used for the crossover, but it also can take place at a freeway interchange. The decision about when to use contraflow, under what conditions, for how long, and how to communicate the information to the public usually falls on state governors, although they often task local law enforcement and state departments of transportation to manage the operations. The main criteria for deciding whether to use contraflow

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

procedures are the characteristics of the hurricane (i.e., size, intensity, track, track speed), traffic volume, setup time, time of day, land use, and traffic conditions and patterns. By the time barricades are erected, traffic is cleared, and law enforcement is positioned, it can take 12 hours or more just to prepare a contraflow. Although contraflow operations are beneficial in providing increased evacuation capacity, the procedure can be inconvenient, confusing, unsafe, labor intensive, and difficult to enforce. Overall, the costversus-benefits remains unknown.

Several research efforts will be necessary for effective emergency management of the roadway environment. These include development of realtime detailed evacuation models that simulate actual roadway operations and combine various types of weather data with transportation and geographic data in one standardized display. Accomplishing this will require relationships between the meteorological and transportation researchers and practitioners to be further developed. In addition, these research efforts must be combined with tools for communicating reliable real-time information to the public, more complete data regarding the real-time operation of the transportation system, and improved mechanisms for sharing data and information. Institutional issues must also be addressed, as many different agencies and jurisdictions are usually involved in emergency management.

Roadway Design and Construction

Designers and builders of roadways must account for weather in their daily operations and long-term planning. For example, air temperature, humidity, wind, and precipitation play a fundamental role in the drying, hardening, and shaping of both concrete and asphalt. Ideally roads should be strong enough to carry loads, be durable and have low permeability to resist water and chemical penetration, be resistant to cracks and chemicals to prevent deterioration, and be aesthetically pleasing. However, for concrete, hot weather (75 to 100°F) can (1) accelerate setting, which inhibits a smooth finish; (2) increase the concrete temperature, which reduces the long-term strength of the pavement; and (3) increase the rate of hydration, which causes shrinkage and cracks. On the other hand, cold weather (< 40°F) can slow hydration, which retards hardening and strengthening (Smith, 2003). For asphalt the surface temperature before the mix is laid is critical, with higher surface temperatures (> 55°F) required for thinner slabs and cooler temperatures (> 35°F) allowed for thicker slabs (Spaid, 2004). Precipitation of any kind or amount can be very detrimental to concrete or asphalt construction. Liquid precipitation can create an imbalance in the

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

FIGURE 3-23 Schematic showing how temperature and moisture differentials above and below a concrete slab can cause it to curl up or down. SOURCE: Harold Smith, Center for Transportation Research and Education, Iowa State University.

moisture load, while hail can damage the surface, especially during the first 4 to 6 hours of placement. For asphalt, rain can wash away the tack coat placed on the surface before the mix is laid, leading to costly cleanup and replacement. Differences in temperature and moisture on either side of a concrete slab can cause it to curl (Figure 3-23).

The effect of weather on roadway construction goes beyond physical damage; it has an economic impact as well. Money can be lost even before paving begins if weather prohibits concrete or asphalt from being poured. For instance, concrete mixture can remain in the truck for only 30 minutes, so the mixture may have to be dumped if unexpected high winds or precipitation occurs. Inaccurately forecast or sudden storms also can result in lost wages for idle paving crews. Once the pavement has been placed, hail or rain can damage a slab to the extent that total removal ($8 to $10 per square yard) and reconstruction ($25 per square yard) are warranted. If only superficial damage is done, the concrete can be diamond grinded ($4 to $8 per

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

square yard) to restore its surface (Smith, 2003). Even with notice of inclement weather there is some loss in production as work is suspended and the pavement is covered to minimize damage, then uncovered to resume paving. Despite such efforts, surface damage still may ensue. Ideally contractors want better than 85 percent accuracy with a minimum 0.5- to 2.0-hour notice for at least a 2 km2 or smaller grid (Smith, 2003).

Most construction supervisors obtain weather information from the NWS, free Web-based services, and in some cases, specialized forecasts produced by private sector companies. However, the information often is not as timely or on as fine a scale as is needed by the roadway construction community. Decision support tools that meet the needs of the roadway industry are starting to be developed; for example, High Performance Paving is a prediction tool specific to the roadway construction community that uses temperature, wind, and humidity information to predict optimum paving windows and the impacts of adverse weather on roadway construction (see http://www.hiperpav.com). The weather information needs of the construction community were recognized by the inclusion of the Maintenance and Construction Operations user service in the National ITS Architecture in 2002.

INTELLIGENT TRANSPORTATION SYSTEMS

A major effort of the last decade by the surface transportation community has been to design and implement ITS. These systems take detection, computer, and communication technologies and apply them in an integrated fashion to increase the safety and efficiency of road transportation. For example, ITS is employed in Minneapolis and St. Paul, Minnesota, using a network of real-time freeway traffic detectors as part of a ramp metering system. The traffic flow information from the detectors is used as input to automated freeway capacity algorithms that regulate entry of additional vehicles onto the freeway system through modified traffic lights located at the entry ramps. Almost all state and local transportation authorities are using ITS to some extent today. ITS can be vehicle-based systems (e.g., adaptive cruise control, rear object detection) or infrastructure-based systems (e.g., vehicle surveillance, dynamic message signs). Typically it is the interaction between vehicles, the roadside, management centers, and travelers along with the synergy of data and information flows working in harmony that yield spectacular results.

Linking vehicles and infrastructure electronically is expected to advance rapidly in the coming years, as it is viewed as a very cost-effective

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

means of improving safety and mobility. The application of sophisticated technologies in an integrated fashion across a number of transportation system components (i.e., vehicles, roadside, centers, and travelers) clearly requires a master plan. The transportation infrastructure (i.e., roadside and centers) in our highly decentralized transportation system must interact with vehicles of many types from many suppliers and travelers of all sorts needing to cover great distances across multiple jurisdictions. The U.S. federal government initiated extensive multistakeholder consultations in the mid-1990s leading to the development of the National ITS Architecture (National ITS Architecture Development Team, 2003). It is essentially a high-level blueprint for the application of information technologies to road transportation. First issued in 1996, the ITS Architecture continues to be refined. In 2000 the Architecture was adopted by Canada with some modifications. It is therefore well on its way to general use over most of North America, an enviable situation to promote freedom of movement and trade throughout the continent as well as collective security and global competitiveness. Indeed, the National ITS Architecture is a major body of work that will influence the evolution of road transportation for decades to come.

Enhanced use of ITS can mitigate some of the negative impacts of weather on road transportation by making it possible to provide the best weather and traffic information to users in a timely and appropriate manner (Andrey et al., 2003b; Cambridge and Mitretek, 2003). For example, in response to reduced surface friction during winter weather conditions, an advanced traffic management system could modify signal timing and ramp metering to adjust vehicle spacing accordingly, alert roadway maintenance crews to treatment needs, and inform drivers in their vehicles of potentially hazardous conditions. Version 4.0 of the National ITS Architecture, introduced in 2002, included the Maintenance and Construction Management Center and the Maintenance and Construction Vehicle to more formally capture road weather and the transportation components mandated to deal with it.

ITS has also been instrumental in the development of standards; for example, a group of communications standards referred to as the National Transportation Communications for ITS Protocol (NTCIP) includes standards for an ESS, NTCIP-ESS, which are open, industry-based standards that facilitate information exchange between RWIS and other ITS devices with a common communications interface. The standardization of terminology and graphical displays as well as the format and structure of messages are under development and will facilitate communication of road weather information to the public. The ESS sensors can be linked to an automatic spray

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×

system, perhaps developed by a different vendor, to dispense freeze-point depressants the instant that snow or icing conditions are detected on the road surface. Likewise, with sensors deployed according to agreed-upon standards in a coherent network over one or more jurisdictions, more sophisticated mesoscale modeling solutions could be pursued. Indeed, ITS provides a framework with which to extend road weather and other services in a fully integrated fashion across the nation, and eventually, throughout North America.

Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
×
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
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Suggested Citation:"3 Current Meteorological and Transportation Activities Relevant to Road Weather." Transportation Research Board and National Research Council. 2004. Where the Weather Meets the Road: A Research Agenda for Improving Road Weather Services. Washington, DC: The National Academies Press. doi: 10.17226/10893.
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Weather has broad and significant effects on the roadway environment. Snow, rain, fog, ice, freezing rain, and other weather conditions can impair the ability of drivers to operate their vehicles safely, significantly reduce roadway capacity, and dramatically increase travel times. Multiple roadway activities, from roadway maintenance and construction to shipping, transit, and police operations, are directly affected by inclement weather.

Some road weather information is available to users currently, however a disconnect remains between current research and operations, and additional research could yield important safety and economic improvements for roadway users. Meteorology, roadway technology, and vehicle systems have evolved to the point where users could be provided with better road weather information through modern information technologies. The combination of these technologies has the potential to significantly increase the efficiency of roadway operations, road capacity, and road safety. Where the Weather Meets the Road provides a roadmap for moving these concepts to reality.

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