UBC Theses and Dissertations
Upstream signalized crossover intersection Tabernero, Vener
The impact of left turns on operation is probably the most significant factor in the performance of conventional intersections. As a result engineers have looked to alternative measures for dealing with left turns at intersections to improve performance, some of which have been unconventional schemes. The purpose of this thesis is to introduce a new unconventional intersection scheme, the Upstream Signalized Crossover (USC), which is a four-legged intersection designed to eliminate left turn opposing conflicts by crossing the left and through traffic to the left side of the road at all four approaches before the intersection. The crisscrossing of traffic upstream of the intersection results in four additional secondary signalized intersections. The operation of the USC intersection was analyzed, along with a typical conventional intersection, using the Highway Capacity Manual (HCM) 2000 methodology and simulation models that were developed using VISSIM. The HCM analysis employed the Syncro software to compute the signal timings and offsets for the multiple signals of the USC. The results from this analysis indicated that a significant reduction in average delays could be achieved by the USC intersection when directly compared to conventional intersections. The average delays computed for the USC was about 45 % to 60% less for the same traffic volumes that caused a sample conventional intersection to fail and was able to accommodate between 15% and 20% more traffic before the USC reached failure. The VISSIM simulation model revealed that the USC was not as sensitive to left turn volumes as compared to conventional intersections and has the potential for handling large left turn volumes while maintaining acceptable levels of performance for through traffic. However, when compared to a conventional intersection the analysis did not show significant improvements in left turn delays for the USC, which may indicate that progression between the primary and secondary signals for the left turn movements were not as favourable. Future analysis of the USC intersection should develop and utilize a more dynamic technique for optimizing the signals for both the through and left turn movements. The USC has 50% less crossing conflicts than a typical four-legged conventional intersection and as a result could offer a significant reduction in left turn opposing collisions. The potential for rear-end collisions could be higher for the USC given the additional signals; however, this should be mitigated by improving the coordination and progression between the signals.
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