A bus driver’s “medical emergency” apparently is what sent his hulking vehicle speeding out of control on a major downtown Duluth street before dawn and crashing into another bus heading the other way, authorities said Wednesday.

The collision shortly after 5 a.m. Tuesday on W. Superior Street killed one passenger on the runaway bus and injured others on both buses.

The passenger who died has been identified as Michael J. Mooney, 53, of Duluth.

“Preliminary indications are the driver of the eastbound bus suffered from a medical emergency,” a statement from police read.

That driver was identified as Frank Polson, 58, of Duluth. Polson received medical treatment immediately after the crash, but there is no further word on his condition.

Polson’s bus hit a stop sign, a traffic signal post and then a construction barrier before it hit the other bus.

The other bus driver was identified by police as Glenn Evan McGill, 59, of Duluth. The Duluth Transit Authority (DTA) said both drivers have many years of experience and received safety awards last week.

This was the first fatality for the authority since its inception in 1969, a DTA official said.

Paul Walsh