Commuters going home on the Virginia Railway Express or MARC trains Wednesday evening will face delays as the trains go slower to avoid running into heat kinks in the tracks.
VRE officials said Wednesday's forecasted temperature of 88 degrees varied so widely from Tuesday's high of 67 degrees that CSX, which owns VRE's tracks, imposed heat-related speed restrictions on VRE's Fredericksburg line.
Riders going all the way to Fredericksburg could be delayed by 11 minutes, though riders going a shorter distance may not notice a delay.
MARC's Camden and Brunswick lines also will have five- to 15-minute heat delays, officials said.
Temperatures that swing from hot to cold can cause metal tracks to expand or contract, creating rail problems in both hot and cold weather.
Metro spokesman Dan Stessel said his agency had no heat-related problems Wednesday.