Round up yellow and all-red times to the nearest ½ second/ Civil Engineering
Given a four-legged pre-timed signalized intersection with one exclusive left turn lane, one through lane and one through/right lane on each approach (all approach and receiving lanes are 12 ft. and there is a 4-foot raised median separating the left turns from the opposing traffic lane), a 35 mph speed limit on all approaches, and the following traffic characteristics –
Peak Hour Volumes EB WB NB SB
Left 107 134 88 106
Through 599 653 432 487
Right 142 135 108 112
PHF 0.9 0.9 0.9 0.9
Arrival Type 4 4 3 3
Other input data – 3% heavy vehicles, no parking, no buses, no bikes or pedestrians, level grade on all approaches, in a non-CBD area.
1. Determine the appropriate yellow and all-red interval to use for each phase. Assume a 10 ft/sec2 deceleration rate, a one second reaction time, and a 20 ft. vehicle length. Round up yellow and all-red times to the nearest ½ second.
2. Assuming protected-only left turns, manually calculate the saturation flow rates for all lane groups. For the exclusive through and through-right lanes, assume the through movements are distributed to equalize the flow ratios.
3. Develop a protected-only left turn phasing plan that minimizes sum of critical v/s.
4. Estimate the optimal cycle length using the HCM Method with Xc = 0.9 and based on the HCM lost time/extension of effective green assumption. Round the estimated optimal cycle length up to the nearest 5 seconds.
5. Calculate all interval timings (critical and non-critical phases) for the optimal (rounded) cycle length.
6. Develop the queue accumulation polygon for the westbound exclusive through lane group and calculate the total uniform delay and average uniform delay per vehicle.
Calculate the incremental delay for the westbound exclusive through lane group and determine the lane group level of service.
