If you take the train to commute to and from Baltimore, you may have run into delays this week amid sweltering temperatures.

Both MARC Train and Amtrak issued heat orders, meaning trains on Brunswick, Camden and Penn Lines are operating slower than usual. Metro SubwayLink trains are also operating at reduced speeds, according to the Maryland Transit Administration.

Paul Shepard, a spokesperson at the MTA, said trains on the Brunswick Line experienced delays on Wednesday ranging from 15 to 25 minutes. On Tuesday, Amtrak warned of delays between 12-8 p.m. along the busy Northeast Corridor.

The region is seeing record-breaking temperatures this week, with a heat index as high as 110 degrees. The high temperatures are caused by a weather phenomenon known as a heat dome, when a ridge of high pressure traps very warm air over an area.

Why do trains slow down in the heat?

When steel, the backbone of railroads, heats and expands, there’s a risk of buckling, where the track snaps out to the side. Trains cannot move when this happens.

Slowing the train down creates less pressure on the steel, which means less force that could cause buckling. Newly installed tracks are more likely to react to high heat and fluctuating temperatures, according to MTA.

CSX Transportation owns the MARC Train Brunswick and Camden Lines. Under its heat orders, the maximum speed is reduced by 20 mph once temperatures hit 85 degrees or vary by 25 degrees in a 24-hour period.

Amtrak, which issues heat orders on the Penn Line, reduces speeds once temperatures top 95 degrees.

Along the Northeast Corridor, Amtrak also has overhead electrical wires that can be impacted by extreme temperatures, causing components to fail. That means Amtrak would have to shut down power to repair the wire, causing a service delay or suspension.

Officials stress that heat orders don’t mean tracks are unsafe, but they’re in place to ensure the safety of passengers and train operators.