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NCHRP 3-74 Chapter 7 Selection of Speed Reduction Treatments at High-Speed Intersections Suggested Research Page 7-1 7 Suggested Research Speed reduction and safety are high priority topics within the transportation profession. The purpose of this NCHRP study was to answer questions specific to speed reduction treatments at high-speed intersections. The research produced guidelines for considering factors at high-speed intersections and a methodology to consider potential treatments. Phase II testing provided valuable data on the specific speed reduction qualities of the following treatments: Peripheral transverse pavement markings, rumble strips, and dynamic warning signs activated by speed. The research team has identified other research topics (in no particular order) for future consideration. ⢠NCHRP 3-74 provides quantitative data on the speed reduction qualities of the tested treatments. However, measuring the safety effects and conducting safety evaluations can potentially take many years to adequately assess the short-, mid-, and long-term effects of a treatment. Future research should be conducted to evaluate the actual safety performance over a three- to five-year period after the treatments have been in place. Of particular interest would be an effort to understand the role of speed and safety versus driver awareness and safety. Future research may shed light on whether (absolute) speed reduction affects safety or whether treatments influence driver attention to potential workload tasks and therefore, aid drivers in avoiding the conflicts they encounter at an intersection (versus a roadway segment). ⢠The research team applied a minimum of a three month period between the before and after testing. This period was applied to balance research projects scheduling needs and the potential Ânovelty effects of the new treatment. In addition, only one set of after data was collected at each testing location. Future research should consider additional testing to understand driver behavior over time and the long term speed reduction effects over time. The studies might consider understanding and quantifying the novelty effect over time and driver acclimation to treatment types over long periods of time. ⢠There are many databases (HSIS, FARS, GES, and HPMS) that summarize various safety performance values applications. These databases do not contain sufficient data variables and elements to reveal the true relationships between speeding and safety at intersections. Causal factors for intersection crashes are complex and are significantly affected by intersection and roadway geometry, traffic control, traffic volume, and the locationÂs general environmental context. Human factors, such as driver behavior and interpretation of the intersection context, are equally as important, and are also unknown. Future research should evaluate current databases to assess if they fully serve safety evaluation needs or if current databases could be successfully modified or if a new database would be valuable. The research would evaluate the intended use of the data, recommend data collection needs, identify crash report data recording protocols, define crash data base input needs, and identify a user interface that allows productive queries and manipulation of the data. ⢠Accurate and precise speed measurement at the various field conditions was challenging. Some of the measuring devices available were precise but not
Chapter 7 NCHRP 3-74 Suggested Research Selection of Speed Reduction Treatments at High-Speed Intersections Page 7-2 necessarily accurate; with measurement accuracies on each device ranging from plus/minus 2-3 mph. Other devices were accurate and precise but were relatively fragile. These devices might pose challenges to night testing (adjusting devices) and testing during less than desirable conditions. Other measuring devices (LIDAR or RADAR) are proven tools. However, these devices may require data collectors to be visible to drivers and possibly affect the testing results. Accurate, durable devices that provide precision while being inconspicuous and easy to use would be helpful in future testing programs. ⢠This study focused on understanding the speed reduction qualities of a single speed reduction treatment. Future studies should be conducted that measure the potential and incremental benefit of combining treatment types. Understanding the potential speed reduction effects of combined treatments could provide additional flexibility to professionals in applying a range of treatments to address a unique intersection need. Similarly, future studies could consider the effects of applying supplemental countermeasures such as ITS or Enforcement to enhance the speed reduction qualities of improvements. ⢠Testing for this project was performed during the best weather possible for before and after measurements. The purpose of this testing approach was to isolate and remove weather conditions from the testing results. Future research could build up on the clear and dry weather testing to understand how night time and other weather conditions affect a treatmentÂs effectiveness. ⢠This research project collected data a limited number of sites for each type of treatment. Future studies should be conducted at a larger number of sites of the same type of treatment to obtain additional speed reduction data and treatment testing results. ⢠NCHRP Report 572 (Based on NCHRP 3-65) Roundabouts in the United States, provides a comprehensive summary of roundabout operations and safety performance. NCHRP 3-65 collected spot speed data at existing roundabout locations throughout the nation. The data was collected for locations 200 feet before the entrance of the roundabout, at the entrance, and at the exits of the roundabouts. Future research could evaluate NCHRP 3-65 speed data for opportunities to evaluate speed performance at roundabouts. ⢠As roundabouts are still relatively new in the United States, there are some reservations to applying them in high speed environments. The FHWA publication Roundabouts: An Informational Guide provides insights about approach curvature and other methods to reduce speed. Those methods and applications have been referenced in this report. Future studies could consider speed reduction applications on roundabout approaches. The findings and study methods may provide insights and be transferable to approach treatments for conventional intersection forms. ⢠Speed tables and other vertical deflection methods are common traffic calming tools. However, there has been no published research or testing results for speed table applications on high-speed facilities or specifically at intersection approaches. Future
NCHRP 3-74 Chapter 7 Selection of Speed Reduction Treatments at High-Speed Intersections Suggested Research Page 7-3 studies could explore speed table applications on lower speed facilities and consider a broader application to facilities with higher speeds. ⢠As the speed reduction qualities of treatments are identified, a logical next step would be to understand the optimal location, design, and specifications to obtain optimum configurations. Future studies (conducted using field testing and/or driving simulators) could test a range of possible configurations and make recommendations for design guidelines. For transverse pavement markings this may include the most effective placement of the markings in relationship to roadway segment and intersection influence areas. This could include near or away from existing signing or at alternative stopping sight distances. In addition future research could consider the number of series of treatments, bar design (widths and spacing), or combinations of peripheral and full transverse markings. Dynamic Warning Signs placement and design should also be investigated in future studies. This could include understanding the influence of sign size and orientation and the types of messages provided. ⢠A number of supplemental lighting and marking devices are now available. The continued creative use of light emitting diodes (LEDs) and fiber optic products creates the opportunity to supplement existing signing and pavement markings. Future studies might consider how these visual aids supplement current devices and traffic control. ⢠Future research could consider driver or traffic attributes such as commuter traffic versus new or unfamiliar motorists. Research could also consider the treatment effectiveness based on driver age range or experience levels (new versus experienced operators). Future research might consider the affects of various fleet types, including large trucks and buses. ⢠The testing results showed that speed values and relationships varied by direction or approach at the same intersection. For example, speeds might have been reduced on one approach but not on another. Future research might consider how to assess and quantify the effects of various contextual environments of upstream segments. This research would help understand the roles and relationships between roadway segments and intersection influence areas. The study efforts could help researchers understand what elements influence driver behavior and how those elements effect driving speed. ⢠This project was able to test stop-sign and uncontrolled intersection approaches. Future research should focus on investigating speed reduction needs and influences of various traffic control types including signalized intersections, four way stops, and yield controlled approaches or movements (such as a dedicated right-turn lane).
