PORTLAND — A mechanical issue may have caused Thursday’s Portland Streetcar crash and derailment, which sent one person to the hospital and tied up streets for hours. Dan Bower, the Portland Streetcar’s executive director, said state investigators are examining a “potential mechanical issue” with the Oregon-built streetcar that was involved in the worst crash in the transit service’s 17-year history. “It wasn’t an operator error,” Bower said Tuesday in an interview, “and it wasn’t a speeding issue.” Bower said he couldn’t say much beyond that, citing the ongoing state investigation.