You can probably guess most of the important safety systems in a light rail vehicle. Brakes probably top the list. Bumpers are another obvious system that keeps people safe. However, some systems are trickier to guess. For instance, did you know that light rail vehicles carry hundreds of pounds of sand? It came as a complete surprise to me. Why would that be necessary?
It's the same reason that people carry sand in their cars in case it snows: traction control. It’s to prevent slipping and sliding. Of course, snow is rarely a concern in bright and sunny Phoenix. However, it does rain, and it's on those rainy days that the sand comes in handy.
A two or three-car consist train (that’s two or three trains hooked together), can weigh upwards of a quarter million pounds! That’s a lot of momentum rolling down the tracks. If you've ever seen a train wheel, it's relatively smooth and it's a far cry from the road-gripping galvanized rubber on a car or truck. With the help of sand, it makes stopping at platforms and traffic lights a little easier.
A train operator will press a button to have sand sprayed in front of the wheels. The coarse sand provides extra traction helping the train stop in time. The train's traction control can also kick in automatically when the onboard computers sense that the train's wheels are slipping.
So, the next time you're on a light rail train and you see storm clouds overhead Phoenix's normally sunny skies and rain pours from the heavens, listen for a distinctive “PSHH” sound like compressed air being released. That's the traction control kicking in, spraying the sand on the tracks to make sure the train can stop safely.