Four electrical workers leapt off a runaway work vehicle at underground Roosevelt Station on Tuesday, and two were taken to hospitals, according to Sound Transit.

Work remains suspended since the incident, for the whole three-mile corridor from Husky Stadium to Northgate, the agency said.

The workers are contractors for Mass Electric, transit CEO Peter Rogoff told board members Thursday. Mass Electric is installing signals and power equipment there, and has completed many other Northwest projects.

Tuesday’s incident, around 9:20 a.m., began just north of Roosevelt Station, where a “hi-rail vehicle” — basically a pickup truck that also contains railroad wheels — rolled south on the northbound track, an agency statement said.

Four workers jumped off at the station, and the truck finally came to a stop just before the U District Station, nearly a mile south. All were injured, and the two who went to hospitals were released later Tuesday, the agency said.

The route, known as Northgate Link, remains on schedule to open for passengers by September 2021, maybe a few weeks sooner.

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Investigations are underway by Sound Transit’s safety division, by Mass Electric and by the truck supplier, said transit spokesman John Gallagher.

“Safety is a core value of Sound Transit, and the agency will be conducting a thorough investigation as to the cause of this incident before the contractor’s work is allowed to continue,” a transit-agency statement said.

Its safety group is being reorganized this year, under a new acting director, Moises Gutierrez. Rogoff announced the shake-up after blistering reports by the National Transportation Safety Board (NTSB) and a Sound Transit-hired consultant, that blamed management lapses for contributing to a fatal Amtrak crash in late 2017. Two workers have died building the East Link overhead trackways in Bellevue, which will open in 2023.

In 2007, a worker died when a runaway supply train crashed next to the Beacon Hill Tunnel.