Lecture #6

1. Lecture #6 Chapter 16: Principles of Intersection Signalization

2. Objectives • Understand allocation of time and its effects at signalized intersections • Understand effect of design parameters on operations • Understand concept of delay and how it relates to the traffic stream

3. Modeling Intersection Departures • For an hour of green, how many departures can there be? s = saturation flow rate, vphgpl h = saturation headway, sec 3600 = seconds per hour

4. Modeling Intersection Departures • For an hour of green, how many departures can there be? (revisited)

5. Modeling Intersection Departures • So, how much time does it take to clear a queue? • T = Time to clear a queue, sec • l1 = Start-up lost time, sec • h = Saturation headway, sec • N = Number of vehicles in the queue, veh

6. Modeling Intersection Departures • How much time do we have to clear a queue? gi = effective green time for movement i, sec Yi = Sum of yellow plus all-red time for movement i, sec t1 = start-up lost time, sec tL = total lost time per phase, sec, tL=t1 + t2 t2 = clearance lost time, sec

7. Modeling Intersection Departures • For one hour of operation, how many vehicles can be served? ci = capacity of lanes serving movement i, vph or vphpl si = saturation flow rate for movement i, vphg or vphgpl gi = effective green time for movement i, sec C = signal cycle length, sec

8. An Example Intersection • Task 1: Allocate the green time to the critical movements • Task 2: Find the optimum cycle length

9. An Example Intersection • What do you need to know? • Demand volumes = {see figure} • Saturation flow rates = 3600/2 = 1800 vphgpl • Lost time (tL) • Start-up (t1)= 2 sec/phase • Clearance (t2)= 1.5 sec/phase • Number of phases (N) = 2 phases/cycle • Lane configuration = number of lanes • Time available = 3600 sec/hr

10. An Example Intersection • How much time do we have for service? TG = time available for effective green allocation within the hour N = number of phases in a cycle C = cycle length, sec tL = total lost time per phase, sec, tL=t1 + t2

11. An Example Intersection • How many vehicles can we serve? TG = time available for effective green allocation within the hour h = Saturation headway, sec Vc = maximum sum of critical lane volumes, vph

12. An Example Intersection • What is the shortest cycle that can serve the demand volumes? • Solve for C: • Substitute VEB+VNB = Vc • Do you see any problems with this cycle length?

13. An Example Intersection • How can we adjust the cycle length in a way that would address these problems?

14. Left Turn Vehicles • What different intersection geometric designs are used to accommodate left turns? • Shared lane • Exclusive left turn lane

15. Left Turn Vehicles • How can traffic signals provide service to left turns? • Permitted • Protected • Protected-permitted combination

16. Adjusting for Left Turn Vehicles Using Through Vehicle Equivalency • What is through vehicle equivalency? • fLT = left turn adjustment factor • PLT = proportion of left-turning vehicles • ELT = left-turn equivalent • so = saturation flow rate for through vehicles • s = adjusted saturation flow rate In the same amount of time {say 50 sec}, the left lane discharges 10 through vehicles and 5 left-turning vehicles, while the right lane discharges 25 through vehicles.

17. Conclusion • New Homework Assignment: • Check web for HWK #3 • Homework Assignment due: • Assignment #2 • Lab Announcements • Data collection Monday, next week