U.S. Department of Transportation
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: FHWA-HRT-09-002 Date: Jan/Feb 2009|
Publication Number: FHWA-HRT-09-002
Issue No: Vol. 72 No. 4
Date: Jan/Feb 2009
Below are brief descriptions of products recently published online by the Federal Highway Administration's (FHWA) Office of Research, Development, and Technology. Some of the publications also may be available from the National Technical Information Service (NTIS). In some cases, limited copies are available from the Research and Technology (R&T) Product Distribution Center.
When ordering from NTIS, include the NTIS publication number (PB number) and the publication title. You also may visit the NTIS Web site at www.ntis.gov to order publications online. Call NTIS for current prices. For customers outside the United States, Canada, and Mexico, the cost is usually double the listed price. Address requests to:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Toll-free number: 800-553-NTIS (6847)
Address requests for items available from:
Federal Highway Administration
R&T Product Distribution Center, HRTS-03
For more information on R&T publications from FHWA, visit FHWA's Web site at www.fhwa.dot.gov, the Turner-Fairbank Highway Research Center's Web site at www.fhwa.dot.gov/research/tfhrc/, the National Transportation Library's Web site at http://ntl.bts.gov, or the OneDOT information network at http://dotlibrary.dot.gov.
Minimum Retroreflectivity Levels For Blue and Brown Traffic Signs
Publication No. FHWA-HRT-08-029
In 2003, FHWA published research recommendations for minimum maintained retroreflectivity (MR) levels for most traffic signs but excluded white-on-blue and white-on-brown signs. The 2003 recommendations for MR levels were based on conditions representing dark, rural environments. This new report describes the research activities and findings related to the development of recommendations for MR levels for white-on-blue and white-on-brown signs. The report also includes recommendations from an investigation related to MR levels needed for complex visual conditions, including glare from oncoming headlamps and fixed roadway lighting.
The researchers used a summary of pertinent literature to develop an experimental plan to produce luminance thresholds that could be used with a previously developed analytical model to develop a set of recommendations for MR levels for white-on-blue and white-on-brown signs. The researchers integrated the results for these signs into one table with the current set of MR levels and consolidated both legend and symbol signs into the same recommendations because of similar requirements for luminance thresholds.
The report is available at www.fhwa.dot.gov/publications/research/safety/08029/index.cfm and from NTIS under order number PB2008111445. Printed copies also are available from FHWA's R&T Product Distribution Center.
Safety Evaluation of Increasing Retroreflectivity Of STOP Signs
Publication No. FHWA-HRT-08-041
FHWA organized a pooled fund study involving 26 States to evaluate low-cost safety strategies as part of FHWA's strategic highway safety effort. One of the strategies evaluated was STOP signs with increased retroreflectivity. This strategy aims to reduce the frequency of crashes related to drivers being unaware of STOP signs at unsignalized intersections.
Researchers obtained geometric, traffic, and crash data at unsignalized intersections from 231 sites in Connecticut and 108 sites in South Carolina. In each case, the researchers installed STOP signs with increased retroreflectivity. Next, the researchers incorporated Empirical Bayes (EB) methods (a statistical calculation) in a before-and-after analysis to determine the safety effectiveness of increasing the sign retroreflectivity.
The study revealed a statistically significant reduction in rear-end crashes in South Carolina. Based on the results of the disaggregate analysis, the researchers found reductions in crashes at three-legged intersections and intersections with low approach volumes. The analysis also indicated a slight reduction in nighttime- and injury-related crashes in Connecticut and South Carolina, but the results were not statistically significant. The researchers determined that a much larger sample size would be needed to detect a significant effect in these types of crashes.
Given the low cost of installing STOP signs with increased retroreflectivity, even with conservative assumptions, only a modest reduction in crashes is needed to justify their use. Therefore, this strategy has the potential to reduce crashes cost effectively, particularly at lower volume intersections.
The report is available at www.fhwa.dot.gov/publications/research/safety/08041/index.cfm and from NTIS under order number PB2008110098.
Safety Evaluation of Installing Center Two-Way Left-Turn Lanes on Two-Lane Roads
Publication No. FHWA-HRT-08-042
Another strategy chosen to be evaluated in FHWA's pooled fund study was the installation of center two-way left-turn lanes on two-lane roads. The goal of this strategy is to reduce the frequency of crashes involving a turning vehicle, which could be classified as head-on or rear-end crashes.
Researchers obtained geometric, traffic, and crash data for 78 sites in North Carolina, 34.9 kilometers, km (21.7 miles, mi) of roadway; 10 sites in Illinois, 9.7 km (6.0 mi); 31 sites in California, 10.95 km (6.8 mi); and 25 sites in Arkansas, 21.25 km (13.2 mi). The researchers incorporated EB methods in a before-and-after analysis to determine the safety effectiveness of installing the two-way left-turn lanes. The study revealed a statistically significant reduction in total and rear-end crashes in each of the States where the installations were evaluated. Rural installations proved to be more effective in reducing crashes than urban ones.
The researchers concluded that installations of these types of lanes can be a cost-effective treatment for two-lane rural roads, especially those with a high frequency of rear- end collisions involving a vehicle trying to make a turn.
The report is available at www.fhwa.dot.gov/publications/research/safety/08042/index.cfm and from NTIS under order number PB2008110100.
Safety Evaluation of STOP AHEAD Pavement Markings
Publication No. FHWA-HRT-08-043
This report on STOP AHEAD pavement markings was part of an FHWA pooled fund study to evaluate low-cost safety strategies to reduce the frequency of crashes related to drivers being unaware of stop control at unsignalized intersections.
Researchers obtained geometric, traffic, and crash data at unsignalized intersections for 8 sites in Arkansas, 9 sites in Maryland, and 158 sites in Minnesota. To account for potential selection bias and regression to the mean, the researchers conducted an EB before-and-after analysis to determine the safety effectiveness of installing STOP AHEAD pavement markings. Results of the aggregate analysis indicate a statistically significant reduction in total crashes at the Arkansas and Maryland sites. The combined aggregate analysis for these two States indicates a reduction of at least 15 percent in total crashes. The study also revealed a statistically significant reduction in right-angle and rear-end crashes at the Arkansas sites. Injury crashes dropped as well in Arkansas and Maryland, as the study found a statistically significant crash reduction of 10 percent for the two States combined. The results for Minnesota were not included in the main analysis but support the conclusion that this strategy is effective in improving safety.
The disaggregate analysis indicated that crash reductions are highly significant at three-legged intersections and significantly greater than reductions at four-legged intersections. The strategy also proved more effective at intersections with all-way stop-control (AWSC). Given the low cost of this strategy, even with conservative assumptions, only a modest reduction in crashes is needed to justify its use. Based on the estimated safety effectiveness of STOP AHEAD pavement markings, the researchers concluded that the necessary crash reduction to obtain a 2:1 benefit-cost ratio is easily achieved. Therefore, this strategy has the potential to reduce crashes cost effectively at unsignalized intersections, particularly at three-legged and AWSC intersections.
The report is available at www.fhwa.dot.gov/publications/research/safety/08043/index.cfm and from NTIS under order number PB2008111181.
Safety Evaluation of Flashing Beacons at STOP-Controlled Intersections
Publication No. FHWA-HRT-08-044
This report on flashing beacons was part of an FHWA pooled fund study. Researchers studied three types of flashing beacons—intersection control beacons, beacons mounted on STOP signs, and actuated beacons—at stop-controlled intersections. The purpose of this strategy is to reduce the frequency of crashes related to drivers being unaware of stop signs at unsignalized intersections.
Researchers obtained geometric, traffic, and crash data at stop-controlled intersections for 64 sites in North Carolina and 42 sites in South Carolina. The researchers incorporated EB methods in a before-and-after analysis to determine the safety effectiveness of installing flashing beacons, while accounting for potential selection bias and regression-to-the-mean effects.
Overall, installation of flashing beacons in North Carolina resulted in statistically significant reductions in total, angle, and injury plus fatal crashes. The intersections in South Carolina experienced little change following the introduction of flashing beacons. The combined results from both States support that an angle crash reduction of 13 percent and an injury and fatal crash reduction of 10 percent can be expected. The economic analysis based on the combined results for angle and nonangle crashes from both States indicates that standard flashing beacons and some of the actuated ones (that is, the less expensive beacons) are economically justified, but that a benefit-cost ratio of 2:1 might not be achievable for the more expensive beacon types.
The report is available at www.fhwa.dot.gov/publications/research/safety/08044/index.cfm and from NTIS under order number PB2008111182.