The driver of a dump truck that collided with two pedestrians Wednesday morning, killing one and critically injuring the other, likely lost consciousness before the crash, Pittsburgh police said.

‘‘The driver operates his own construction company and was delivering breakfast to a job site when he lost consciousness, possibly on Arlington Avenue,’’ Pittsburgh public safety spokeswoman Sonya Toler said in a news release.

The man’s one-ton dump truck, traveling west on East Carson Street, veered off the road near the Smithfield Street Bridge, crossed a sidewalk and struck two pedestrians as they tried to cross the street about 6:40 a.m., police said.

One of the pedestrians, Christopher Williams, 43, of Carrick, died. Another, a woman whose name has not been released, was taken to UPMC Mercy, where she was treated for a head wound and remained in critical condition Wednesday.

Investigators used green paint to mark two pavement irregularities about 60 yards before the crash scene. One was a hole about 8 inches in diameter that formed around the mouth of a buried pipe. The other was a small rut less than an inch deep.

Ms. Toler said police examined those holes as part of their investigation and also planned to evaluate whether the dump truck might have malfunctioned in any way.

The intersection remained closed during much of the morning rush hour.

Another crash during the morning rush blocked the inbound Parkway North near Mount Nebo Road, causing traffic to back up well beyond the Interstate 79 split and beyond the Pennsylvania Turnpike.

A third crash blocked inbound Route 28 at Etna, forcing traffic to be diverted off the road. An Allegheny County dispatch shift commander said two were injured in that crash, which was reported at 6:37 a.m. One patient had back pain and the other a possible broken leg.

First Published: November 19, 2014, 12:40 p.m.
Updated: November 20, 2014, 4:22 a.m.