Safety and Operational Characteristics of Two-way Left-turn LanesThe purpose of this research was to evaluate the safety and operational characteristics of two-way left-turn lanes (TWLTLs) compared to four-lane undivided roadways in Minnesota. Research tasks to achieve this purpose consisted of a comprehensive literature review, data collection from the identified study sites, and statistical data analysis. Nine study sites were selected, located throughout the state of Minnesota. Operational and crash data were analyzed before and after the conversion from a four-lane undivided roadway to a three-lane roadway with a TWLTL. The results of a yoked/group comparison analysis showed statistically significant reductions in total crashes, PDO crashes and left turn crashes. The percentage reductions in total crashes, PDO crashes and left turn crashes after the conversion were approximately 37 percent, 46 percent and 24 percent, respectively. The reductions in crash rates for total crashes and PDO crashes were found statistically significant and the percentage reductions were 46 percent and 45 percent, respectively. Additionally, the change in the mean speed and 85th percentile speed were found statistically significant, but in both cases the change was less than two miles per hour. The results of this research show that safety characteristics of a roadway are improved when a four-lane undivided roadway is converted to a three-lane roadway with a TWLTL when daily traffic volumes are less than 17,500 vehicles per day. |
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85th percentile speed Alexandria analysis APPENDIX approximately arterial Ave W average average crashes City Cold Spring commercial developments compared comparison sites considered consists countermeasure crash data crash rate cross-section decrease direction driver Duluth effectiveness estimate evaluate existing factors Fairview Fatal FIGURE five five-lane four four-lane to three-lane four-lane undivided roadway given Grand Ave Grand Avenue Group Comparison Approach identified implemented improvements included increase injury crashes intersection Jefferson land lane left turn located median methodology methods Michigan mile Minnesota MNTH 29 MNTH 61 observed operational paired parking Paul pavement percent percentage reduction period Pierce Butler procedures recorded Reduction in Crashes reported road diet roadway segment safety safety and operational similar Standard Deviation statistically significant Street study sites Table three-lane conversion three-lane roadway Total Crashes traditional traffic traveling treatment TWLTL two-way vehicles Wentworth Avenue