dc.description.abstract |
Despite considerable safety measures implemented by traffic and transportation engineers, speeding
continues to be a significant safety problem on the highway network, both in the United States and
other countries. Even though higher traffic volumes and more travel occur in urban areas, majority of
fatal crashes occur in rural areas indicating the significance of the issue. When high-speed roadways
pass right through the small towns in rural areas there are considerable drops in speed limits, making
proper speed management critically important. However managing speed has always been a challenge
particularly in rural communities due to the low budgets available leading to lower levels of
enforcement. It is therefore necessary to identify effective, low-cost approaches to control speeds in
such areas.
Optical Speed Bar (OSB) treatment is one such approach, where transverse pavement makings are put
in place with gradually deceasing spacing giving the drivers the perception of going faster than they
actually are traveling. This research attempted to evaluate the effectiveness of OSBs in reducing
approach speeds on two-lane, rural divided highways approaching small communities. Each approach
had one lane and speed drop was either from 65 mph to 45 mph (4 sites) or from 55 mph to 30 mph (1
site). Speeds data were collected and analyzed both before and after installation of the optical speed
bars at the five ssites. Effectiveness of the bars was evaluated using changes in mean and 85* percentile
speeds under different categories by considering all vehicles, vehicle classification (two axles vs. more
than two axles), days of the week (weekdays vs. weekends), and time of day (daytime vs. nighttime). The
t-testforthe sample mean and the F-test of variance were used to determine significant differences in
speeds among datasets. Significant reductions in mean speeds and speed variance were observed at
the end of the OSBs at four of the five sites, and one site showed no statistically significant change in
speeds. Speed reductions were higher during daytime and weekdays. Higher speed reductions for twoaxle
vehicles were observed, with the exception of one test site. Daytime speeds and speeds of two axle
vehicles decreased the most at almost all test sites. However speeds analyzed farther downstream of
the treatments gave indication that speed reductions were not maintained for a long distance.
However, when considering the low cost associated with the treatment, optical speed bars might be a
good solution to control approach speeds in small communities. |
en_US |