Title page for ETD etd-03312006-120306

Type of Document Master's Thesis
Author Jayadevan, Athira Swarna
URN etd-03312006-120306
Title Effect of Speed Limit Increase on Crash Rate on Rural Two-Lane Highways in Louisiana
Degree Master of Science in Civil Engineering (M.S.C.E.)
Department Civil & Environmental Engineering
Advisory Committee
Advisor Name Title
Chester G. Wilmot Committee Chair
John B. Metcalf Committee Member
Sherif Ishak Committee Member
  • speed limit
  • crash rate
  • safety
  • effect
  • rural two-lane
Date of Defense 2006-03-28
Availability unrestricted
Though the rural two lane roads are the low volume-less traveled roads, the majority of the crashes occur on these roads and the high speed of motor vehicles on these roads is suspected to be one of the main causes for this. This study focused on the development of a methodology to study the impact of a speed limit increase on the crash rate on the rural two lane roads in Louisiana. The Louisiana crash database obtained from the Louisiana Department of Transportation (LADOTD) was used to carry out the analysis. The analysis consisted of the comparison of crash rates of different severity and crash types before and after a speed limit change on rural road sections with same crash type. The comparison was done statistically using a single-tailed paired t-test on each of the homogeneous data groups established using the SPSS add-in, Answer Tree. Answer Tree Analysis ensured that the homogeneous groups established were controlled for the several factors contributing to high crash rates so that the effect of speed limit change alone could be captured, keeping the other factors unchanged within each homogeneous group. The roadway sections were divided into speed limit change and no speed change sections and the crash trends were observed and tested for significance in the no speed limit change sections. The speed limit change group was divided into before and after speed change sections and the after speed change crash rate values were adjusted for any significant trend in the corresponding cases. These final before and after crash rate values adjusted for the trend were compared statistically to test the null hypothesis that crash rate does not increase with speed limit increase, at 5% level of significance. Based on the results, the null hypothesis was rejected for 6 out of the 39 cases while we failed to reject the null hypothesis for the rest of the cases thus indicating that for these cases, we do not have sufficient evidence to say that the crash rate increased with a speed limit increase.
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