Tommy Meehan wrote:The sensor referred to is in the southwest corner of the intersection. Wouldn't that control eastbound traffic on Commerce Street?Preemption #1 (per other documents filed) was an "ALL RED". The diagram (in both your and Dutch's links) shows that it DETECTS cars turning off of the parkway and on to Commerce Street toward the tracks. I have seen similar loops used to preempt green lights when traffic is backed up (for example, not allowing Commerce Street traffic to cross the parkway when there is no room for a vehicle between the parkway and the tracks).
In this case, a vehicle on the detector for 5 seconds would trigger "ALL RED" for a maximum of 45 seconds, then the normal cycle would return.
The normal cycle was at least 40 seconds of green on the parkway, staying green until a vehicle approached from Commerce St. Once a vehicle was detected the Commerce St signal would turn green for 6 to 25 seconds to allow traffic to enter or cross the parkway (minimum 6 seconds until no vehicle was detected - maximum 25 seconds if vehicles were still detected).
"Preemption #2 is activated by the railroad (See Figure 5) and provides green time for vehicles traveling eastbound on Commerce Street to clear the queue (cars). If the train preemption is activated the traffic signal will terminate the active green phase, run the corresponding yellow and red clearances, and turn green for vehicles traveling eastbound on Commerce Street only. This phase will remain green for a minimum of 2 seconds and a maximum of 10 seconds. Once the maximum of 10 seconds is reached the traffic signal will run the yellow and red clearance times and turn green on the Taconic State Parkway and cycle normally."
The timing was changed to 29 seconds of green then 4 seconds of yellow (enough for a semi on the wrong side of the tracks to clear the tracks and the area between the tracks and the parkway). 2-10 seconds was way too short. Enough to clear ONE car of of the track if everyone between the tracks and the parkway moved forward immediately - but not enough time if anyone had a slow reaction to the green. They also changed the priority of the railroad preemption but did not say what had higher priority in the past.
A good preemption will follow #2 above except with enough time for the drivers to react and the traffic to clear. If I were designing this intersection I'd probably hold Commerce Street approaching the tracks at red (do not cross the parkway) until the train passed, which would "solve" the problem of cars crossing the intersection without anywhere to go. (But obviously the railroad should always be #1 in priority ... in this case granting a green light to traffic exiting Commerce St toward the parkway when a train was present regardless of the presence of backed up traffic headed toward the tracks.)