Moderators: CRail, sery2831
MBTA3247 wrote:Didn't Brookline wire up the signals on Beacon Street for signal priority a decade ago?Yes! And when they did it they offered priority to the T. The T's response was that they wanted to study the affects it would have on the service before spending money on the extra hardware, and they wanted Brookline to fund the study. Brookline (rightfully, in my opinion) told the T to pound sand, and so nothing happened. Fast forward the decade, and eureka! We could have signal priority!
Disney Guy wrote:Transit signal priority might not work that well with bus (or trolley) stops before the intersection (near side stops). If an operator opens the door again to board another passenger, then the time reserved for priority passage of the bus or trolley gets wasted and other traffic is delayed with no benefit to transit.Certain optical sensors work that way. An infrared camera mounted on the top of the trolley signal detects the shape of the vehicle as it approaches and can trigger a signal cycle based on proximity. When there's a station stop the detector notices the change in front marker light aspect on the trolley when the doors close and the flashing lights go solid, and uses that as the trigger to scramble a go signal. Fairly simple and elegant in execution as it doesn't require any change in ops practices or installation of any 2-way radio infrastructure. Brookline assumed the T was most likely to adopt a system like this when it was doing over all the signals on the Beacon corridor.
What is needed is an on board system whereby the transit vehicle, notably a two or three car train, cannot signal its presence to the traffic signal if any door is open and the motorman must hold down a button to request priority and that also prevents any doors from being opened.
Disney Guy wrote:The system described "can make the green arrive up to 14 seconds earlier and can extend the green up to 8 more seconds." I agree that the benefits would not be that great of the overall red light could last say 60 to 100 seconds.,Also an important consideration, being able to control the left turn signals at some intersections. There are several intersections where non turning traffic could be allowed to proceed, while the left turn lane could be held until the train has cleared the crossing.
What is needed is to be able to insert short green lights for transit in between the subphases of a long red light. For example if, on an east-west trolley route, a cross street has separate phases for northbound and southbound mixed traffic, an east-west trolley only phase could be created on demand between the northbound and southbound cross street phases. In addition a trolley phase could occur both before and after a left turn phase for the same street as the trolley route instead of the either-or (always before vs. always after) we use today. Now, these insertions are not going to occur in every possible place on every cycle so the impact on general traffic should not be that great.
This could eliminate, say, a 25 to 40 second chunk of waiting time from the trolley route.
A hypothetical (long and technical) system is described here: http://www.cockam.com/serveme.htm