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 l 1 = 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? g i = effective green time for movement i, sec Y i = Sum of yellow plus all-red time for movement i, sec t 1 = start-up lost time, sec t L = total lost time per phase, sec, t L =t 1 + t 2 t 2 = clearance lost time, sec

7. Modeling Intersection Departures For one hour of operation, how many vehicles can be served? c i = capacity of lanes serving movement i, vph or vphpl s i = saturation flow rate for movement i, vphg or vphgpl g i = 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 (t L ) Start-up (t 1 )= 2 sec/phase Clearance (t 2 )= 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? T G = time available for effective green allocation within the hour N=number of phases in a cycle C=cycle length, sec t L =total lost time per phase, sec, t L =t 1 + t 2

11. An Example Intersection How many vehicles can we serve? T G =time available for effective green allocation within the hour h=Saturation headway, sec V c =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 V EB +V NB = V c – 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? f LT =left turn adjustment factor P LT =proportion of left-turning vehicles E LT =left-turn equivalent s o =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