Virginia Railway Express passengers can expect some delays Wednesday night as the extreme heat forces trains to slow down during the evening commute.

VRE officials said CSX, which owns the rail used by the Fredericksburg Line trains, has issued heat orders for Wednesday. People can expect delays of 10 to 15 minutes this evening, depending on other train movement at the time, VRE officials said. As of noon, Norfolk Southern, which owns the rail used by the Manassas Line trains, had not issued any heat restrictions.

Trains must slow during extreme heat because the steel rails will expand, VRE officials said. Although this expansion is taken into consideration during the construction period, there are occasions when the expansion can cause a “sun kink,” or a shift in the track that causes a curve in an otherwise straight pair of rails.

Rail officials will monitor the tracks throughout the day and if weather conditions change, restrictions could be lifted, VRE officials said.