Evaluation of bypass lane safety, operations, and design in Kansas.

Details

• Creators:
  Dissanayake, Sunanda ; Esfandabadi, Alireza Shams
• Corporate Creators:
  Kansas State University. Transportation Center
• Subject/TRT Terms:
  • Bypasses
  • Traffic lanes
  • Three leg intersections
  • Four leg intersections
  • Highway safety
  • Before and after studies
  • Cross sectional studies
  • Rural highways
  • Highway design
  • Evaluation
  More +
• Publication/ Report Number:
  K-TRAN: KSU-12-1
• Resource Type:
  Tech Report
• Geographical Coverage:
  Kansas
• Corporate Publisher:
  Kansas. Dept. of Transportation
• Abstract:
  The construction of bypass lanes at rural intersections has typically been considered a low-cost highway safety ; improvement by the transportation community. However, this needs to be quantitatively evaluated so that decisions can be made ; on whether to continue adding bypass lanes. Highway safety analyses utilize two common approaches to evaluate the effectiveness ; of a treatment: before-and-after study and cross-sectional study, both of which were utilized in this study. For the before-and-after ; study approach, this research performed paired sample t-test statistical analysis to estimate changes in total crash frequencies, ; crash rates, Equivalent Property Damage Only (EPDO) crash frequencies, and EPDO crash rates at intersections 3 to 5 years after ; the addition of bypass lanes, compared to 3 to 5 years before bypass lane additions. Crash data between 1990 and 2011 were ; obtained from the Kansas Crash and Analysis Record System (KCARS), maintained by the Kansas Department of Transportation ; (KDOT). For the cross-sectional study, intersections with bypass lanes were compared to intersections with no bypass lanes, for ; which crash data were obtained for more than 1,100 intersections in Kansas. ; According to the before-and-after study, bypass lanes improve safety at unsignalized rural intersections. Total number of ; crashes and crash severity decreased after bypass lane additions, but these reductions were not statistically significant at a 95% ; confidence level for the majority of cases. For intersection-related crashes, however, a statistically significant reduction in crash ; rates occurred after the addition of bypass lanes at three-legged intersections. By lowering the confidence level to 90%, however, ; more categories become significant for both three-legged and four-legged intersections. ; In the cross-sectional study, number of crashes and crash severities were lower at three-legged intersections with bypass ; lanes compared to three-legged intersections without bypass lanes, even though these reductions were not statistically significant at ; a 95% level. When considering a 300-ft intersection box, statistically significant crash reductions occurred at four-legged ; intersections, for all considered crash and crash rate categories. When considering 90% level, crash reduction at three-legged ; intersections was also statistically significant when considering a 300-ft intersection box. ; Crash Modification Factors (CMFs) calculated to evaluate safety effectiveness of bypass lanes at unsignalized rural ; intersections in Kansas showed values less than 1.0 for almost all cases, indicating safety benefits of bypass lanes. ; Overall, this study concludes that bypass lanes are beneficial in improving safety in rural areas, even though they may not ; be advisable in high volume conditions. Accordingly, there is no harm in continuing with the practice of adding shoulder bypass ; lanes at rural unsignalized intersections where the traffic volumes are relatively low.
  More +
• Format:
  PDF
• Funding:
  C1917
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/29204/dot_29204_DS1.pdf
• File Type:
  [PDF - 1.44 MB]
• Collection(s):
  University Transportation Centers ; US Transportation Collection
• Main Document Checksum:
  urn:sha256:51376e9149caf490b68c3a7dd5af35364a89648918f80b071da07a952ef49f52