The most significant crash and derailment in Portland Streetcar history occurred after a screw "came loose" and lodged in the vehicle's throttle, according to a preliminary investigation.

A Portland Streetcar train crashed into two vehicles on May 24 in the Central Eastside, ultimately resulting in a derailment and sending one person to a local hospital with injuries.

Three minutes before the crash, the streetcar operator reported to dispatch that the throttle was "sticking in the engaged position." The streetcar driver was able to get the throttle out of that position, but only "with more force than normally required," according to a press release.

The handle mechanism, or throttle, controls the streetcar' speed and braking. The operator was unable to pull the handle back to slow down the streetcar. When the operator takes their hand off the throttle, it's supposed to spring backward and stop the vehicle. That didn't happen.

Oregon Department of Transportation's rail division started investigating the crash and preliminary information determined a screw in the streetcar's master controller, a component of the transit service's dashboard, was loose and "lodged" in the vehicle's throttle.

Streetcar officials immediately pulled similar models purchased from the now-defunct United Streetcar company as a precaution. Those vehicles were deemed safe.

The agency said it had "developed a preventive maintenance plan to ensure regular inspection of the specific screw involved" and has contacted the manufacturer of the master controller assembly for any additional guidance in maintaining the component.

A full investigation will be released later this year.

The crash occurred at Southeast Grand Avenue and Taylor Street.

-- Andrew Theen