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.

light rail, Valley Metro
A Valley Metro technician checks the level of one of four sand reservoirs on a light rail vehicle

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.

light rail, Valley Metro
A light rail vehicle is parked for maintenance. The silo behind it is filled with sand for trains.

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.

light rail, Valley Metro
LRV Lead Maintenance Technician Roger Gonzalez and the pump that’s used to refill train sand reservoirs

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.

Alex Tsotsos
Operations Communications Specialist
Writer, editor, musician, gamer, and former news professional. Frequently seen at Phoenix Rising matches and jogging around Gainey Ranch. May throw things in the presence of typos.