Home > Transit > Transit Signal Priority – A driver’s perspective

Transit Signal Priority – A driver’s perspective

November 3, 2011 Leave a comment Go to comments

Choose Your Way Bellevue has an interview on their site with John Toone, the Intelligent Transportation Systems (ITS) program manager at King County Metro.  John discusses Transit Signal Priority as well as other signal enhancements along the B line – It’s worth a look.

When the RapidRide B line started up in October, signal priority was still not active.  As I drove the route I’d frequently get stuck at red lights, hardly an unusual experience when driving a bus.  Over the subsequent weeks, as signal priority has been turned on, I’ve noticed the effects of signal priority.  In more and more cases “stale green” lights, which Metro trains us to watch for and be prepared to stop at, would stay green long enough to let me catch the light.  I actually found this transition a bit disorienting since I usually approach most stale green lights intent on stopping.  With TSP active, I find myself making far more lights so I’ve modified the way I approach these “stale green” lights.  I keep a bit more speed coming into the lights I expect to stay green but still low enough that I can safely stop.  (As John told me in an email, it’s signal priority not preemption, so I’m not always guaranteed a green light)

After speaking with Metro planners, I’ve learned that most of the signals along the B line that were scheduled to have TSP are up and running.  Despite that, there is still some tuning to be done.  On a recent series of trips, my coach was detected anywhere from 19-25 times out of 33 currently active prioritized intersections.  Apparently, there are still some adjustments to be made to the wireless system along the route to detect the coaches.  I’m told the work is ongoing and that I should see further improvements over the coming month.

There are also some intersections that don’t have TSP, which I approach the old fashioned way – foot hovering above the brake and accelerator ready to smoothly stop.  (I strongly suspect NE 24th St & 152nd Ave NE and NE 40th & 156th Ave NE in Redmond are without TSP.  If I’m wrong, then they need tuning 😉  I’m working hard to be patient since I can only imagine the ripple effects of giving too much priority to my bus.  I try to picture my bus cutting a rough line through a gently rippling pond.  The trick for the traffic planners is to make that cut as smooth as possible and not disrupt the other ripples too much.

I’ll add future updates as I hear about or see further changes.  In short, while signal priority will never be a substitute for dedicated right of way, it is already making improvements in travel time for RapidRide.  As the kinks continue to get worked out, I look forward to seeing even more improvements.

NOTE:  Since I drive RapidRide in the morning, my experience is relatively limited.  I’m sure the afternoon trips, with their much heavier traffic, are a bigger test for the system.  Keep that in mind when drawing any conclusions from reading my impressions.  I’m looking for a vacation relief assignment on RapidRide in the afternoon to drive but so far I haven’t seen one.

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  1. Oran
    November 4, 2011 at 4:09 pm

    Is there a way to communicate that signal priority is active and given to the bus driver? Kind of like how Link train operators get a flashing signal as notice of impending signal change. Or like the tiny blue light at S Bellevue?

    • November 4, 2011 at 8:08 pm

      Not that we’ve been told about. There are a couple of those little blue lights on some signals but we’ve received no training on them nor have I seen any pattern indicating that they are connected with TSP. (The one that comes to mind is on the signal at Redmond Way & 148th)

  2. November 4, 2011 at 5:46 pm

    It doesn’t work if you are on time or early only if you are late.

  3. Metro ITS
    November 7, 2011 at 9:27 am

    Here’s some info related to the two questions”

    – At this time the industry doesn’t have products that do two-way communciation between the bus and signal. Our on-board system has the technical capability bus not the software to display that to the driver. The real challenge is to get a signal controller that generates a return message.

    – Our TSP system can use on-time status as a criteria, but our policy is to decrease the scheduled travel time and improve trip reliability. So, all trips are eligible for priority. Regardless, RapidRide runs on headway, not schedule, so buses aren’t late they are out of position. We try to make the wait time as regular as possible.

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