How do MetroLink trains stop safely?
As you may have heard, on Monday night two D.C. area subway trains collided during rush hour. The accident occurred when one vehicle struck another vehicle, which was stopped on the tracks waiting for the passenger platform to clear at the next station. Sadly, nine people were killed, including the train’s operator, and over 70 people were treated for injuries. Investigation into the cause of the crash is ongoing.
Whenever an accident like this occurs, it naturally makes people wonder about the safety of their own local transit system. We asked Training Specialist Suzanne Whitehead to explain some of the safety precautions in place on the MetroLink system that work to prevent this kind of accident. One safety measure is the cab signaling system, which Suzanne explained to me:
MetroLink uses cab signaling to determine the appropriate speed at which a train can travel based on the curve of the track, elevation, etc. The cab signal is sent through the rails to the train which is picked up by an antennae on the train. The Train Operator receives a cab speed on their dashboard so they know what speed to travel between 5 MPH and 55 MPH. When the trains travel at the designated cab speed, all the trains stay on schedule and stay separated from each other. If a train goes over the cab speed for a section of track the operator receives an audible alarm reminding them to slow down, if the train continues at the overspeed, a penalty stop will occur automatically. A penalty stop is a safety precaution built into the train system to stop the train from going at excessive speeds.
Another feature designed to prevent collisions is a system that prevents more than one train from being in the same stretch of tracks at a time. This is called a positive train control system. Suzanne says:
This system divides track sections into blocks. Each block can only accommodate one train at a time. The logic built into the MetroLink system prevents trains from running into each other. When a MetroLink train is stopped in a block and the following train reaches that block’s limits, the system’s logic gives the MetroLink operator in the following train a Zero Cab Speed Signal. This zero cab signal stops the train. The MetroLink Operator contacts the Operations Control Center (OCC) over the radio to report a zero cab signal. OCC may authorize an operator to continue in Yard Mode which overrides the cab signaling system. Yard mode restricts the train to no more than 15 miles per hour. This restricted speed is a speed which will permit the stopping of a train within half the range of the operator’s vision, short of other trains or obstructions. Operators are trained to proceed cautiously while operating a train in yard mode.
I also found out that Metro does not use automatic operation of trains. All MetroLink trains are operated manually by the train operator, and a train will not move unless the operator has told it to do so. This way, should some malfunction in these systems arise, the operator is in control of the train. Being a light rail system rather than a heavier subway system, and with only two cars per train, MetroLink trains are also easier to stop in an emergency.
These are the precautions that we have taken in order to move people as safely as possible. If you have any additional questions regarding the safety features of MetroLink trains, please do not hesitate to post them here.