SAN DIEGO (CBS 8) – An elderly woman was killed when her car stalled on northbound Interstate 5 and was struck by another vehicle near Via De La Valle early Wednesday morning. The chain-reaction crash caused a four car pileup that blocked traffic for hours during the morning commute.

The multi-vehicle crash happened shortly before 5:00 a.m., after a Nissan Sentra stranded in the fast, northbound lane was struck from behind by a Honda Accord driven by a 40-year-old man. That crash then caused a chain of collisions on the freeway.

"If your vehicle is damaged, there's a flat tire. If there's any way you can get over to her shoulder, even if your vehicle is damaged or you have a flat tire try to get your vehicle off the highway as best you can,” said CHP officer Jake Sanchez.

The reason why the Nissan was stopped was unknown. The driver in that car, an 85-year-old woman from La Mesa, did not survive.

"She stopped we don't know why,” continued Sanchez. “We don't know if you run out of gas, you could've been a medical thing. We don't know because we're still investigating that part."

The man who rear-ended the Nissan was transported to Scripps La Jolla with minor injuries. The other two drivers were not hurt.

Immediately following the crash, all northbound lanes were blocked on I-5 approaching Via de la Valle. Only the carpool lane and the off-ramp to Via De La Valle remained open while emergency crews cleared the scene.

All lanes were open on northbound I-5 at 8:00 a.m.

The crash remains under investigation.