Photo by Don Shall on Flickr.

Why do trains on MARC’s Camden and Brunswick Lines sometimes run slowly? One reason is the weather: CSX, which owns the tracks, orders MARC trains to slow down for safety when it’s hot or very rainy.

That’s what CSX Vice President for Passenger Operations Jay Westbrook told the MARC Riders Advisory Council last week. High temperatures can make the rails buckle. If a train goes over a buckle or sun kink, the train may derail, as Amtrak’s Capitol Limited did near Kensington in 2002. Meanwhile, a lot of rain can wash out the track bed, causing the tracks to collapse.

Heat is a problem because modern railroads use continuous welded rail, rather than jointed track. Continuous welded rail is sections of rail that are 1/4-mile long, with the ends welded to the next section of rail. Unlike jointed track, there are no gaps between the sections of rail to accommodate expansion when the rail gets hot. Instead, the rail spikes, tie plates, rail anchors, and track ballast are supposed to keep the rail in place.

The Federal Railroad Adminstration requires track owners to have a plan for continuous welded rail. The plan must include procedures governing train speed on continuous welded rail track when “the difference between the average rail temperature and the average rail neutral temperature is in a range that causes buckling-prone conditions to be present at a specific location.”

CSX owns the tracks on MARC’s Brunswick and Camden Lines. CSX issues a heat order for operations between 1 pm and 7 pm if the predicted high temperature for the day is 90 degrees or higher, or if there is a large predicted change in temperature (e.g., 25 degrees or more), especially if the predicted high temperature is higher than 85 degrees. Large predicted changes in temperature are usually the reason for heat orders in the fall or spring.

If CSX issues a heat order, passenger trains must go 20 miles per hour below the maximum authorized speed, but not less than 40 miles per hour. Freight trains must go at least 10 miles per hour below the speed limit, but not less than 30 miles per hour. On the Brunswick and Camden Line tracks, under normal operations, the maximum authorized speed is 79 miles per hour for passenger trains and 60 miles per hour for freight trains.

Thus, for example, the usual maximum speed for a passenger train with a heat order would be 59 miles per hour. However, if the maximum authorized speed for a particular section of track were 45 miles per hour, then under a heat order, the passenger train would go 40 miles per hour, not 25 miles per hour.

The slower speeds not only help the engineers look out for buckles but also prevent buckling in the first place, because a slower train puts less stress on the track, Westbrook said.

For rain, said Westbrook, CSX currently uses Accuweather’s Skyguard service, which provides weather information for specific locations. Skyguard issues flash flood warnings based on recent rainfall, the predicted hourly rainfall rate (more than 1 inch per hour or 3 inches per 3 hours), the total predicted rainfall, and local conditions, such as elevation and soil. Under flash flood warnings, the maximum speed is 40 miles per hour.