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Edition:Final report; June 4, 2009-Sept. 30, 2011.
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Abstract:This study analyzes the influence of several site characteristics on the operational behavior of motorists when passing bicyclists on wider outside through lanes. More than 2000 videotaped passing events were analyzed. Several measures of effectiveness were used in this analysis, including: lateral separation between the motor vehicle and bicyclist; motor vehicle shift to the inside lane; motor vehicle outside through lane usage; and motor vehicle speeds before, during and after passing bicyclists. Regression analysis was used to examine the lateral separation between the motor vehicle and bicyclist, vehicle lateral shift to the inside lane, and motor vehicle outside through lane usage. Motor vehicle speeds were analyzed using a paired-t test. The results show that motorists pass closer to bicyclists when a bicyclist is a male, the outside through lane is narrower, motor vehicles are in the adjacent inside lanes, and the overtaking motor vehicle is smaller. The study findings suggest the frequency and percentage of movement into the adjacent inside lane by overtaking drivers increases with a decrease in the width of the outside through lane. Lateral movement into the inside lanes was also found to increase when the bicyclist was female and when volume of traffic increased. Compact cars had less lateral shift than other vehicle types. The results further show that there is a tendency of motorists to move from the outside through lane to inside lane after recognizing that there is a bicyclist downstream. Generally, drivers reduced speeds when passing bicyclists and then accelerated after passing bicyclists.
This study also developed crash modification factors (CMFs) for asymmetric curb and gutter four-lane roadways with a flush, two-way left-turn lane (TWLTL) and raised median. The results show that given a 24-ft total lane width for inside and outside through lanes, restriping the outside through lane to provide 13 ft and leaving the inside lane with 11 ft would result in a slight reduction of crashes for four-lane sections with raised median. The results further show that if an extra half a foot is added to the outside asymmetric lane to make it 13.5 ft, while keeping the inside lane width at 11 ft, a decrease in crashes is found for both four-lane sections with raised median and four-lane with TWLTL median.
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