How do they do that? Part II

How do the street signal lights know to stay green a little longer or turn from red to green a little sooner when Metro Rapid and Metro Orange Line buses are approaching?

After our original post some of you asked about train signal preemption, which is not the same thing as the signal priority technology used for buses. It’s a totally different beast that we can certainly talk about later.

You also asked about the Orange Line. The Orange Line is not rail but bus service on an exclusive right-of-way. Because it’s a bus, it’s allowed priority like other Rapid lines. Priority does not mean the Orange Line or Rapids avoid getting red lights. It simply reduces the amount of time a bus will have to sit at a red light with early or extended green time.

Someone pointed out that the Orange Line seems to stop for a particularly long time at one or more intersections and wondered why that might be. The Orange Line runs through a few complicated intersections where buses do get red lights. The system was intentionally designed that way with safety in mind.

Also, the way signal priority works, if a bus is not granted priority or misses it for some reason, the bus will get a normal red light cycle, which can be quite long at some intersections. Only one bus approximately every 2-3 minutes will get priority so that the signal has cycle time to recover. So once one bus gets priority, it will lock out another in that 2-3 minutes. That could account for a waiting time that seems longer than you might expect.

3 replies

  1. As you mention, they provided signal sync on Washington, not signal preemption like on marmion way. As such, the blue line still has to slow down and stop for a few moments at a time. It’s not optimal. Also, the section between the EL structure and the subway tunnel on the east side gold line does have many light issues (although the temple avenue intersection stopping will be eliminated once the regional connector is built).

    As far as the other municipalities cooperating with signal sync or preferably preemption, I hope you are right that once LA metrorail is taken seriously, they will change, but that seems unlikely. I mean, the blue line in long beach has been open for quite a long time now and that still has not been addressed at all. And Santa Monica shows no willingness to even sync the lights for expo on Colorado (despite their plea for street running) let alone preemption. Preemption is what we need on all street running sections of Metrorail hands down.

  2. Connor

    No need to be so pessimistic. LADOT did get around to fixing the Blue Line on Washington street with signal synchronization and signal preemption on the Gold Line in Marmion Way. Those two areas used to be slow zones of their respective lines.

    LADOT still needs to get around to improving the gold line on 1st street (though every time I have ridden it did not seem to be an issue there), the orange line, and make sure the Expo line does not get slowed down by traffic.

    The other respective organizations involved that need to get their act together would be Long Beach Transit for Blue Line in Long Beach, LA County Dept of Public Works for the Gold Line on 3rd Street. Im not sure what could be done to get them to cooperate but I’m hoping that as the systems gets built out they will feel more pressure to be proactive about this.

  3. Thanks for posting this. This goes to show how utterly backwards we are with transit here in LA. These lines are implemented as afterthoughts among a sea of traffic engineering overwhelmingly dedicated to cars. The orange line is the pinnacle example of this and how the lights are so abysmally configured for it. This is also true of the east side gold line and the blue line.

    “The system was intentionally designed that way with safety in mind.” How is that safe? There are many, many systems worldwide with open intersection crossings that are preempted. Are those somehow unsafe systems which have been tried and true for years? I don’t think so. Metro holds no water in that rationalization for such lousy design. A single bus crossing a street at moderate speed is no more unsafe than hundreds of cars going through with synced traffic lights which is the case for most arterials in LA.

    Why is it that single occupancy autos, which can go on any street, absolutely must not wait 20 more seconds for a preempted train or bus yet said transit vehicles on dedicated fixed route lines must do so regularly? Why is it that the “level of service” or LOS of an intersection is only considered within the scope of motorists but transit service be dammed.

    These are the reasons people want more grade separation. Traffic engineers here are never going to allow preemption. It ain’t happenin’. As much as I wish that were not the case, and as much as at-grade proponents like to say “well, as long as the line has preemption or priority it will be fine” there seems to be no path to this problem being solved solely because there is a sheer unwillingness to do so. It’s not about cost, its about an ideological difference in what is believed to be the role or lack thereof of rapid transit lines in the very fabric of Los Angeles.