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Publication Number: FHWA-HRT-09-061
Date: February 2010
Simulator Evaluation of Low-Cost Safety Improvements on Rural Two-Lane Undivided Roads: Nighttime Delineation for Curves and Traffic Calming for Small Towns
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For calming traffic in small towns, the results of the current experiment identified two relatively low-cost safety solutions as being worthy of further study and consideration: (1) providing for and encouraging parking in the town and (2) adding painted chicanes to the town entrances. However, the above results have not been validated in the field. As noted previously, simulations of driving through small towns do not take into account all hazardous factors involved in driving through real small towns. In order to achieve adequate field validation, several recommendations are suggested on how to proceed with these two potential solutions.
Adding parking to both sides of the main street in the town was an effective traffic-calming technique in this experiment. However, a field test in a small rural town should be conducted with cars parked on the main street both during the day and at night. If the town has present parking spaces which are underutilized, cars could be artificially introduced by renting a number of used cars from an automobile dealer and/or by parking rarely used private or public vehicles on the main road for a specified duration (several weeks, months, etc.). The density of parked cars could be changed radically from a normal sparse parking density to an experimentally introduced high parking density. As was suggested for streaming PMDs, a before/after/before field test might be devised where driving speed and deceleration would be measured both before and in the town. Such measurements would be made before the implementation of an increased density of parked cars had been put in place, during such an experimental implementation, and after the parked cars had been removed. A baseline speed, followed by a significant decrease in speed during the treatment and a return to the baseline would be the measure of success.
If the field test proved successful, long-term implementation might be attempted to create a higher density of parked cars in the town during times when traffic calming is most needed. A campaign might be launched to encourage more parking at appropriate times. Businesses and government entities could be encouraged to park cars on the main street instead of in parking lots and driveways. Public events and town meetings could specify parking on the main street. Public service and utility trucks could be requested to park on the main street when not in use. Such an increase in the number of parked cars is likely to be a very low-cost option if underutilized parking spaces are already available in the town or if parking can be easily implemented without any changes to the width of the main street or to any curb and gutter layout which might be present.
In the suggested field test scenarios using parked cars, especially in cases of only one travel lane in each direction, special attention needs to be given to assessing and balancing the possible safety hazards of vehicles, drivers, passengers, and pedestrians spontaneously entering the roadway. An additional consideration is the accommodation of bicycle traffic. Although the parked cars condition proved successful in slowing drivers down in the simulator, the suggestion to implement a parked cars solution in the real world needs further investigation.
Based on the results of the current experiment, the most cost-effective solution for traffic calming in small towns is using painted chicanes. For extremely small towns (under 1,000 people), this may be the only affordable traffic-calming implementation. If the main street were wide enough at the beginning and end of the town or if some parking spaces could be eliminated at these locations, painted chicanes might be implemented with minimal cost. A small town might be selected which possesses these necessary characteristics. Painted chicanes could be implemented on an experimental basis. A before/after field test might be conducted where deceleration and speed were measured through the town. If a somewhat longer experimental "after" period were employed (e.g., 3 months) after 1 month of only painted chicanes, flexible vertical yellow delineators could be added to the painted chicanes for the second month and then removed for the third month. In this way, flexible yellow delineators could be tested for their ability to deter drivers from cutting the corners on the painted chicanes.
The recommended field test is only of the before/after design because it might be difficult to remove the pavement paint once applied. Also, if effective, continued implementation would prolong possible benefits. In the current experiment, the painted chicanes were effective in slowing down traffic at the beginning and end of the town. However, between the chicanes in the middle of the town, drivers tended to accelerate and drive at higher speeds. A combination of the parked cars and painted chicanes solutions could prove beneficial in this regard. If a higher density of parking could be encouraged even only in the middle portion of the town, the complementary advantages of both treatment types might be realized. This combination might be tested in a second field study in a different town.
In the above suggested field test scenarios using painted chicanes, especially in cases without a separating median, attention needs to be given to assessing and balancing the possible safety hazards of head-on or sideswipe opposite-direction crashes. In general, both bulb-outs and chicanes should only be implemented in well lit areas.
The current experiment focused on two areas: (1) advanced detection and speed reduction for curves in rural two-lane roads at night and (2) traffic calming for small rural towns during the day. For curves, PMDs with edge lines performed better in terms of slowing drivers down than pavement markings alone. The streaming PMDs solution with edge lines offered the most dramatic potential benefit in terms of advanced curve detection, and it is worthy of further study and consideration. In towns, chicanes slowed drivers down the most followed by parked cars on both sides of the road. As possible low-cost safety improvements (provided adequate field validation), adding painted chicanes to town entrances and providing and encouraging parking in the town are worthy of further study and consideration.
This experiment was conducted by the joint effort of many individuals and organizations. The authors wish to acknowledge valuable contributions from the following individuals: Raymond Krammes, Roya Amjadi, and Carol Tan for guidance and insight; Thomas Granda for oversight and support; Paul Tremont, William Perez, and Stephen Fleger for management and review; Pascal Beuse for data analysis, graphics, and editing; Lindsey Clark and Dana Duke for laboratory support; and FHWA HDS staff members Barry Wallick, Jason Williams, Peter Chou, Ryan Cartwright, and Michael Baumgartner for creating and sustaining the driving simulation. Thomas Welch from the Iowa Department of Transportation and Thomas Broderick from the Massachusetts Highway Department provided information on speed calming in small towns. Gilbert Soles from the Florida Department of Transportation provided information on streaming light patterns for roadway delineation. The authors also wish to acknowledge valuable contributions from the following organizations: the FHWA Turner-Fairbank Highway Research Center for providing laboratory facilities and staff and the Technical Advisory Committee for the Low Cost Safety Improvements Pooled Fund Study for providing input and direction from the perspective of engineering practice.
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