05-17-2017, 01:27 PM
(05-17-2017, 12:28 PM)Canard Wrote: Can you imagine how complex the software must be to coordinate all the requests for priority signaling - especially once ion starts, and we throw that into the mix?
As a software guy, and based on everything I've read about the signal priority, my educated guess is that you give the complexity far too much credit!
All of the signal priority is based around simply pre-empting the light's planned timed phase.
They will at most be doing shortened reds, and held greens. These are timed to fit within the light's preprogrammed signal cycle. It will always be (for example) 3 minutes for a full cycle, but when a bus requests signal priority, the exact timing within that 3 minutes gets adjusted.
A bus that's behind schedule, will issue a signal priority request to each eligible traffic signal along the way. The traffic signal will read that, and then extend the current green, or shorten the current red as much as it can. The next red or green will be shorter by an equal amount. If another bus comes along in that time, then there's nothing the signal can do, as it needs to catch back up. There's a limit to how many vehicles can take advantage of signal priority.
All this points to each signal being independent, and nothing coordinates between signals.
As for ION, we've seen the detectors in the track bed. I imagine that ION will simply request the same kind of signal priority. I bet that any GRT buses running parallel won't get signal priority at all, so as not to interfere. And as for crossings at railway corridors, GRT will certainly have to wait for ION trains regardless.