1. Lec 24, Ch.19: Actuated signals and detectors (Objectives) Learn terminology related to actuated signals Understand why and where actuated signals are used Learn how to determine detector locations Learn how semi-,full-actuated, volume-density signals work Know how presence and passage detectors work

2. What we discuss in class today… Variation in arrival demand  good for actuated signals Types of actuated control Types of detection Actuated control features and operation Signal timing parameters and detector placement Examples of semi-actuated and full- actuated controls

3. Variation in arrival demand Pretimed signals operate with constant cycle lengths, phase sequence, and interval timings  Capacity with a pretimed controller is constant. When demand varies significantly from time to time, either green time is wasted or queue forms. In a coordinated system, however, all signals must operate on a single fixed cycle length to maintain offsets and progression patterns  Actuated controllers are not good for such cases Wasted green Queue forming

4. Actuated control and controllers The cycle length, phase splits, even the phase sequence may vary from cycle to cycle. Semi-actuated control Detection only on minor side-street approaches; green remain on the main until a “call” for service on the side street is registered. Full-actuated control All approaches have detectors; equal importance of the direction of traffic; for relatively isolated intersections; Volume-density control Basically functions like full-actuated control; good for high-speed approaches (>= 45 mph); Has extra features to adjust initial timing and reduce the gap extension during green extension time

5. Detection type Point detection (“passage” type)  A single detector is placed for each approach lane to be actuated.  The detector relays information as to whether a vehicle has passed over the detector. Area detection (“presence” type)  Generally used in conjunction with volume-density controllers.  The importance is placed on the existence of a vehicle (s) in the detection area.  They “count” the number of vehicles stored in the detection area.

6. Actuated control features and operation  Minimum green time (Initial green + unit extension)  Passage time interval  Maximum green time  Recall switch (unless the subsequent phase has the recall “on” green remains to the previous phase unless demand exists)  Yellow and all red

7. Additional features of the volume- density controller Variable initial timingGap reduction &

8. How the maximum green time works

9. How the maximum green time works (cont)

12. Signal timing parameters and detector placement Minimum green time: Passage time and the allowable gap (the time it takes a vehicle to travel from the detector to the stop line at its approach speed): If P computed is impractically small, it has to be increased. P computed becomes the minimum value. Typically between 3 and 4 seconds are used.

13. Signal timing parameters and detector placement (cont) Maximum green time:  Usually set by working out an optimal cycle length and phase splits as if the controller were pretimed. Then, multiply this value by 1.25 or 1.5 to set the maximum greens. Then, allocate green to the phases.

14. Signal timing parameters and detector placement (cont) Some detector location strategies (p.547): Method 1: Method 2 (use 3 to 4 sec allowable gaps): (See page 547 for discussions.)

15. Signal timing parameters and detector placement (cont) Some agencies have suggested values:

16. Signal timing parameters and detector placement (cont) Pedestrian requirements: The minimum green seldom meets pedestrian requirements. Hence, a pedestrian push-button and an actuated pedestrian phase are needed. Yellow and all-red intervals:

17. Semi-actuated control design example (pp.548-551)  Detector location and min green  Passage time and allowable gap  Maximum green time  Min main street green  Yellow and all-red intervals  Pedestrian requirements

18. Full-actuated control example (pp.551-554)