Light rail is a great mode of transportation. It's energy efficient, it can get through traffic thanks to its dedicated guideway, and it offers superb access to some of the best areas of Phoenix, Mesa, and Tempe. However, it has its limitations. The tracks are at street level, and while that offers amazing accessibility for our riders, there are also times when the tracks can be blocked. Getting by those blockages takes a lot of coordination, and that's all orchestrated where I work at the light rail and streetcar Operations Control Center.
Simply put, there are only two light rail tracks. One goes east and is known as Track One, while the other goes west and is called Track Two. When all goes well, the trains are on their respective tracks and everyone gets to their destinations on time. However, there are times when things happen that shut down one or even both tracks. Usually this is due to vehicles that have run up on the curb next to a track and can't get off without assistance. That's called a "high-center." There are also more serious vehicle accidents that cause an entire section of track to be closed, along with planned track closures due to construction.
Let's look at how light rail controllers will respond to a closure. In the graphic below, there's a blockage indicated by the large X on Track Two, the westbound track, near platform B.
In this case, the line controllers will employ a single-track procedure. They'll tell the westbound train on Track Two to use the switch west of platform C to go onto Track One. The eastbound train on Track One will be told to hold its position during this time. The westbound train will service platform B, bypassing the blockage, and then use another switch to return to Track Two. Then the eastbound train will be cleared to proceed on its normal route. In the meantime, the next westbound train may have to wait at platform A for the eastbound train to clear Track One.
This is a very simplified example; normally there will be two to three platforms that will have to be serviced in a single-tracking situation. The greater the distance covered by the single-track, the longer trains may have to wait for trains going the opposite direction to clear the track.
When both tracks are blocked, light rail line controllers will coordinate with bus controllers to organize a bus bridge. Here's an example:
In this case, something has happened that has blocked both of the tracks leading to platform B. Here’s what will happen.
- The eastbound train at the lower left of the diagram will be emptied of eastbound passengers at platform A and turn around, using the switch to go onto Track Two.
- The westbound train at the upper right will be emptied of westbound passengers at platform C and turn around, using the switch to go onto Track One.
- A bus will pick up the passengers at Platform A, service the area in the platform B section, and let them off at the platform C section where they can pick up the next train. The bus will then pick up passengers at platform C and circle back to platform A.
Hopefully this has given you a little perspective on why it’s sometimes necessary for light rail trains to wait in place for longer than you’d like. Just keep in mind that line controllers never want this to happen and when it does, it’s all in the name of service and safety. To stay in the loop on service disruptions, keep an eye on Valley Metro’s Twitter feed and download the VMAlert app (iOS/Android) for updates.