Fundamentals of Transportation/Traffic Signals/Homework
1. Define the following terms
A. Signal phase Answers: A signal phase is the signal combinations in a signal controller that controls a group of traffic movement off and on. B. Signal cycle Answers: The loop time for a specific traffic phase. The time length between the starting of the phase to it apears again. C. Max-out Answers: the maximum flow of the approach D. Gap-out Answers: the flow of approach accounting for the time of green light period E. Lost time Answers: sources of "lost time" at a signalized intersection are: Start-up lost time, clearance lost time and the yield the pedestrians.
2. A pretimed signal controls a four-way intersection with no turning permitted and zero lost time. The EB and WB traffic volumes are 900 and 800veh/h, and the two movements share the same effective green and effective red portions of cycles. The NB and SB directions also share cycle times, with volumes of 300 and 250 veh/h, respectively. If the saturation flow of all approaches is 1800veh/h, the cycle length is 75 seconds, and D/D/1 queuing applies, determine the effective red and green times that must be allocated to each directions combination (N-S, E-W) to minimize the total vehicle delay and compute the total delay per cycle.
3 AADT (Average Annual Daily Traffic) data on a single intersection between an arterial street (East-West) and a minor street (North-South) has been collected for the current year. Approximate saturation flow rates and collected traffic volumes are given in the table below.
|Approach||Volume (veh/hr)||Saturation Flow (veh/hr)|
|North Bound (NB)||380||1200|
|South Bound (SB)||295||1200|
|East Bound Left Turn (EBLT)||260||1800|
|East Bound (EB)||1160||3000|
|West Bound Left Turn (WBLT)||250||1800|
|West Bound (WB)||1050||3000|
Based on the traffic demand forecast, it is expected demand for the EB and WB directions (including left turn traffic) will increase by 10% each in the next year, and that for the NB and SB directions by 5% each, while the saturated flow rates remain unchanged. The traffic demand has changed so significantly that, as a city traffic engineer, you are asked to develop a new signal design at this intersection for the NEXT YEAR.
A. The design is required by the city to be a three-phase cycle with leading left turn and no overlap. Draw a sketch of the intersection with arrows indicating the directions of traffic to illustrate your design.
B. The signal at this intersection is traffic-actuated, but you are going to work out a pre-timed signal design in your proposal. Describe the differences between a pre-time signal and a traffic-actuated signal. Under which circumstance a pre-timed signal design can be used for a traffic-actuated signal?
C. You are also asked to develop an alternative design for this intersection because the city received complaints of too much travel delay at this intersection. Based on the calculated cycle length, how are you going to develop this plan?