Dallas Area Rapid Transit spokesman Moran Lyons says Wednesday morning's accident involved a Trinity Railway Express train going about 55 mph.
Officials did not immediately identify the victim, who was hit while near a trestle and dead at the scene.
Lyons says nobody on board the westbound train was injured.
DART and the Fort Worth Transportation Authority co-own the Trinity Railway Express. The system provides commuter rail service between Dallas and Fort Worth.