A Pico Rivera man fell asleep at the wheel of his big rig around 1 a.m. today, causing the truck to go through the guardrail and down an embankment on the northbound I-5 near Osito Canyon.

Adan Flores, 30, was driving a 2009 Freightliner, pulling a load of car batteries, when he went off the road. After the truck came to rest approximately 300 feet down, Flores climbed up to the roadway and flagged down passing motorists.

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Tow truck companies responding to the scene feared that the load, which was inside a shipping container, might separate from the flatbed trailer unless the batteries were offloaded first. They left and are expected to return once the container is empty.

Because of the corrosive and flammable nature of the car batteries, Los Angeles County hazardous material teams were called in to handle the unloading.

Two lanes of northbound traffic were closed and a SigAlert was issued at 5:36 a.m. to facilitate the cleanup. The SigAlert was renewed at noon and is anticipated to be in place until at least 6 p.m.

Crews from the U.S. Forest Service were also on scene because of the incident’s location.