Renewing the National Commitment to the Interstate Highway System: A Foundation for the Future (2019) / Chapter Skim
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Appendix C Vehicle-Miles Traveled: Trends and Implications for the U.S. Interstate Highway System Steven E
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232 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM technologies enable exposure to new travel destinations, provide opportunities for same-day deliveries, and create the prospect for lower-cost travel through vehicle sharing and reductions in the onerousness of travel by virtue of relieving the driver of the need to drive the vehicle -- factors that can induce significant additional travel and affect safety. Visions of empty vehicles shuttling between assignments and low-cost travel in shared, electric, self-driving vehicles bolster scenarios of rapid increases in travel demand, with the fundamental economics of lower cost inducing additional consumption of travel.
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APPENDIX C 233 large baby boomer cohort moving past their peak travel years has lessened their travel demand, auto availability levels have neared saturation, and the flight of urban residents to suburban areas may be playing itself out. Shifts from shared-ride travel, mass transit, and walk modes -- some of the sources for increased VMT -- have less room to drop (Polzin 2006)
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234 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Figure C-2 shows the trend in VMT and VMT per capita since January 1992. As is apparent in the graph, VMT per capita remains slightly below its peak level in the 2003–2004 time frame, but total VMT has rebounded since the recession and is at all-time highs.
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APPENDIX C 235 the consequences of demand growth being concentrated and more likely to require more significant capacity increases than can be tolerated or accommodated by incremental operations improvements of existing infrastructure. As an analogy, a 3-inch snow might be passable, but that same snow blown into 3-foot drifts requires plowing.
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236 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Midwest. When looking at the same issues at the state level, one state -- Michigan -- has shown a population decline since the beginning of the century.
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APPENDIX C 237 Notice that 1,295 counties -- 41 percent of the total -- had declining population since the turn of the century, and 15 had declines of more than 25,000. These population declines would certainly suggest a lessening of pressure for transportation capacity expansion and, perhaps more significantly, undermine the economic base over which transportation infrastructure investments can be supported.
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238 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Urban Versus Rural Interstate Demand Insight into the nature of Interstate demand growth also can be gleaned from looking at the trends with respect to Interstate System availability and utilization in urban and rural areas. As can be seen from Table C-3, system extent and growth are greater in urban areas, and urban area Interstate System volume growth is substantially greater than for rural areas.
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APPENDIX C 239 TABLE C-3 Changes in U.S. Interstate Extent and Use, 1980–2015 Centerline Milesa Lane-Milesb VMT (millions)
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240 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM FIGURE C-6 Role of urban and rural Interstate in accommodating VMT. NOTE: Data are based on state highway agency estimates reported for various functional systems and include 50 states and District of Columbia.
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APPENDIX C 241 system. In 1980–2015, the daily volume on each lane-mile of urban Interstate increased from 9,116 to 14,156, or 5,040 per lane-mile, a 55 percent increase.
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242 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM and economic interaction is well established in history and evidenced by the significant role that transportation plays in the economy and the fabric of society. It has been hypothesized that growth in travel demand associated with individuals is attributable to growth in income and growth in knowledge.
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APPENDIX C 243 This section explores factors that researchers have identified as influencing the demand for travel. The objectives are to 1.
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244 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM governance, and institutional context. These factors are known to influence travel demand and mode choice, hence providing a basis for forecasting future demand.
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APPENDIX C 245 choices, are elements of supply that will influence travelers' actual extent and means of travel. As with consumption of any product or service, there is interplay between supply and demand.
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246 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM VMT and Economic Activity Not surprisingly, VMT is highly correlated with economic activity. As shown in Figure C-10, the long-term trend in GDP and VMT are highly correlated.
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APPENDIX C 247 Household income is highly correlated with travel levels, as income relates to workforce participation (commuting trips) and work-derived income enables the social and retail activities that drive household travel demand.
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248 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Population Characteristics and Travel Behavior Changing population characteristics, specifically the movement of the large baby boom cohort toward retirement and the entrance of the even larger millennial generation into young adulthood, have been the basis for significant speculation regarding travel demand implications. Aging baby boomers are passing their peak travel years (ages 35–55)
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APPENDIX C 249 substitute communications for travel via online shopping, downloading music and videos, and interactive video gaming via the Web. This generation reached adulthood during a recession and, in many cases, accumulated substantial education debt, which slowed their pace of attaining vehicles and independent living.
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250 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM As alluded to in Figure C-9, a host of characteristics of land use, including mix of activities, nature of the transportation network, physical design of transportation elements, presence of alternative mode options, and other factors contribute to the portfolio of land use–related characteristics that collectively influence travel. The economic characteristics of business and government also influence travel.
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APPENDIX C 251 to high-income residents, historic empirical relationships between density and travel may be changing. Influence of Transportation Supply and Performance The gray box in Figure C-9 itemizes aspects of transportation choices and characteristics that influence the demand for travel.
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252 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM of demand as a function of cost and time, compare the percentage change in travel demand in relationship to the percentage change in travel cost or travel time. These relationships give insight into how changes in travel time associated with congestion or circuity (less direct travel path)
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APPENDIX C 253 BOX C-3 Induced Travel Induced travel is the increase in usage of a transportation facility due to a reduction in the cost of travel that results from external changes (e.g., capacity expansion to an existing highway)
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254 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Time cost of travel is relevant to future travel demand in two importance ways. First, roadway congestion associated with demand outgrowing capacity can result in additional travel time expenditures by travelers.
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APPENDIX C 255 toward greater travel. Some of these aspects are further elaborated on in the discussion of self-driving vehicles.
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256 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM public vehicle travel contribute an additional 14 percent. The impact of this VMT is disproportionate to its share of travel by virtue of the fact that these typically larger vehicles, with slower acceleration and deceleration characteristics, have higher levels of energy use and emissions and influence roadway capacity and condition considerably more than do individual personal vehicles.
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APPENDIX C 257 BOX C-5 Technology Impacts on Transportation System Capacity • Greater vehicle occupancy -- hence, fewer vehicles required -- by virtue of technology-enabled ridesharing; • Increased volume by virtue of minimizing incidents and incident delays/ congestion; • Increased volume by virtue of smoothing vehicle flow, which increases throughput; • Increased volume by virtue of closer following distances; • Increased volume through optimized intersection signal systems and lane management; • Increased throughput by virtue of narrower lanes, enabling additional vehicle capacity/lanes on some facilities; • Optimized vehicle logistics/trip circuity via navigation capabilities; • Reduced travel via substitution of communication for travel; • Increased travel via empty shared self-driving vehicles shuttling between vehicle assignments, parking, and service terminal locations; • Increased travel via reduced travel money cost: – reduced insurance costs for safer vehicles, – reduced vehicle capital cost by virtue of sharing capital asset among multiple travelers, – reduced vehicle operating cost by virtue of sharing trips with multiple occupants, – reduced vehicle operating cost by virtue of electrification and logistics optimization anticipated for mobility service providers, – reduced parking/storage costs by virtue of vehicle sharing, – reduced per mile travel roadway infrastructure cost by virtue of greater utilization of facility via self-driving vehicles; • Decreased travel via increased travel money cost: – increased vehicle capital cost due to inclusion of additional technologies and quicker obsolescence, – increased transportation infrastructure cost as infrastructure is modified to accommodate connected and automated vehicles, – increased travel cost if monopoly mobility service providers extract high profits from mobility services, – increased travel costs should reliance on mobility services require contingency investments to accommodate special situations such as emergency evacuations or operations in inclement weather; • Increased travel via reduced travel time "cost": – reduced time cost by virtue of being able to do something of higher value during travel, – reduced time cost by virtue of faster travel speeds on managed or higher-capacity facilities; • Decreased travel via increased travel time "cost": – increased travel time cost by virtue of vehicle arrival wait time and trip circuity for shared travel, – increased travel time cost by virtue of slower travel speeds due to induced travel from lower travel monetary costs, – increased travel time cost by virtue of slower travel associated with strict speed limit requirements and conservative vehicle interface behaviors.
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258 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Forecasts of Future VMT Numerous research efforts have explored modeling VMT trends in an effort to understand future infrastructure needs, energy use, vehicle emissions, traffic accidents, and other considerations impacted by travel demand. Because demand is influenced by a multitude of factors, various strategies and components of demand can be modeled through a number of different means.
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APPENDIX C 259 American Association of State Highway and Transportation Officials ( AASHTO) exemplifies that use.
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260 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM BOX C-7 Future VMT as a Basis for Understanding Future System Performance Treatment of Traffic Growtha For the Highway Economic Requirements System (HERS) analysis in this report, growth in VMT is based on two primary inputs: HPMS section-level forecasts of future annual average daily traffic that states provide and a national-level forecast developed from a new FHWA model.
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APPENDIX C 261 BOX C-8 VMT Forecasting Methodologies and Forecasts Volpe Model and FHWA Forecasts Pickrell et al.
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262 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Guidance Regarding VMT Growth for Future Interstate Initiative Policy Consideration Based on the body of information presented, a number of observations relevant to policy planning activities for future Interstate Highway System transportation investment can be gleaned: 1. It is clear that the current and anticipated future conditions create a significantly large amount of uncertainty regarding future travel demand and system capacity.
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APPENDIX C 263 uncertainty regarding future lane throughput capabilities, diminish the criticality of long-term needs as a prerequisite for investment decisions. Seldom are we building new capacity on our roadway systems for future demand; most often, we are constrained to build capacity for prior or current levels of demand that are not being adequately accommodated today.
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264 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM and financial implications of capacity expansion will create huge challenges and place a premium on capacity expansion strategies that can be deployed within existing facility footprints.
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APPENDIX C 265 Corwin, S., C Giffi, J
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266 NATIONAL COMMITMENT TO THE INTERSTATE HIGHWAY SYSTEM Pickrell, D
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