A train carrying chemicals crashed into a garbage truck Tuesday in suburban Baltimore causing an explosion that rattled homes at least a half-mile away.

ROSEDALE, Md. — Federal investigators planned to spend the coming days piecing together what caused a chemical-carrying CSX train to collide with a garbage truck, derail and explode at a rail crossing in suburban Baltimore.

In the third serious derailment this month, a dozen or so rail cars — at least one carrying hazardous materials — went off the tracks around 2 p.m. Tuesday in Rosedale, Md., a suburb east of Baltimore. Several rail cars caught fire, sending a plume of black and gray smoke into the air that could be seen for miles, and an explosion rattled homes at least a half-mile away.

While local officials breathed a sigh of relief that only one person — the garbage truck driver — was seriously injured and that the chemical fire didn’t pose a greater risk to nearby residents, some areas of inquiry for investigators were beginning to take shape.

Robert Sumwalt of the National Transportation Safety Board said late Tuesday that the collision occurred at a private crossing where the only marking was a stop sign. He said it wasn’t clear why the truck was crossing the tracks or whether it was authorized to be there.

The truck driver, 50-year-old John J. Alban Jr., was in serious condition Tuesday night at Maryland Shock Trauma, a hospital spokesman said. Two CSX workers aboard weren’t hurt.

Both the NTSB and the Federal Railroad Administration are investigating Tuesday’s crash of the 45-car train en route from Selkirk, N.Y., to Waycross, Ga. It contained a variety of products from lumber to printing paper.