Side Street Waits Three Minutes at an Actuated Intersection
At an eight-phase actuated intersection, the side street is a single lane that serves both through and left turns, with its stop line 40 ft back from the near edge of the major-street travel lanes. Residents complain that the side street waits more than three minutes in the morning peak. The controller is a NEMA TS2 rack running a 90-s cycle. Main-street max green is 60 s, side-street minimum green is 5 s, passage time is 3 s, and side-street max green is 30 s. The side-street detector is an inductive loop saw-cut two years ago. A crew's test shows an occasional call but nothing reliable. There is a pedestrian push button on the side street, and the crosswalk across the major street is 48 ft long.
1. How do you determine whether this is a detection failure or a timing/recall problem, and what tests do you run?
Read the worked answer
Separate the call from the response.
Is the controller receiving a call?
- Watch the controller's detector status display (or the detector card LEDs) while a vehicle crosses the loop. No indication means the call never arrives.
- Place a manual test call from the controller keypad or a detector tester. If the phase then serves normally, the logic is fine and the field detector is the problem.
- Measure the loop with an inductance meter and compare against the detector manufacturer's expected range. Also check feeder resistance, splices, and the home-run connections; a two-year-old saw-cut loop frequently fails at a splice or where the lead-in crosses the curb.
- Swap the detector card with a known-good one to rule out the card.
If calls are arriving reliably and the phase still waits, the problem is timing or logic: check recall settings, max green, gap/passage, cycle length, and whether the phase is being skipped by a pedestrian or coordination setting. On a 90-s cycle, a three-minute wait means the phase is being missed entirely, not merely served late.
2. What interim and permanent fixes are available, and what risk does each carry?
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Interim (same day):
- Enable minimum recall (or maximum recall) on the side street. This guarantees the phase is served every cycle even with no detection, and it is the fastest way to restore service while parts are ordered.
- Risk: recall serves the side street whether or not a vehicle is there, which adds unnecessary stops and delay to the 900-vph major street and can increase rear-end crashes. Use minimum recall, not max recall, and document the temporary setting.
- Temporary above-ground detection (video or radar) can bridge the gap if the agency has units.
Permanent:
- Replace or repair the loop - new saw cut with proper sealant, or convert to above-ground detection to avoid future pavement work.
- Repair the splice/lead-in if that is the actual failure point, which is cheaper than a new loop.
Either way, retest with a vehicle and confirm the call registers and the phase serves before removing recall.
3. The crosswalk is 48 ft. What walk and flashing DON'T WALK times do you need, and how do they constrain the vehicle green?
Read the worked answer
Walk interval: a minimum of 7 s, and it should begin at the start of the pedestrian phase.
Pedestrian clearance (flashing DON'T WALK): crossing distance divided by walking speed, using 3.5 ft/s as the standard:
48 / 3.5 = 13.7 s → 14 s
Total pedestrian time = 7 + 14 = 21 s.
Constraint on the vehicle green: the side-street green plus its yellow and red clearance must be long enough to contain the 21-s pedestrian phase. With the current 5-s minimum green and a 3-s passage, the pedestrian phase cannot be completed inside a minimum side-street service - so whenever the button is pressed, the controller must extend the green. That interaction should be verified, not assumed.
Also check the side-street max green of 30 s: it is adequate for 21 s of pedestrian time plus vehicle clearance, but if the left-turn and through movement share the lane and demand is heavy, the 30-s cap may be the actual cause of the queue. If the push button is not pressed, the pedestrian phase may be omitted, which is appropriate - but only if the button actually works.