Traffic was backed up just past Monument Boulevard in Pleasant Hill near the Highway 242 exit just after 9 a.m.
The driver of the truck told Con Fire he was having trouble with his breaks, pulled over to the side of the road and shortly thereafter the vehicle caught fire, according to Con Fire spokesperson Capt. Chris Toler.
The California Highway Patrol said the truck was full of items.
Video in the media player above is from a previous update
Because the truck was equipped with a compressed natural gas system fitted with a safety valve that allowed the fire to burn the fuel off, fire crews let the blaze wind down before moving in to fully douse it, Toler said.
This led officials treating this as a possible hazardous materials situation since whatever what was burning could potentially be toxic.
At one point, all lanes of northbound Highway 242 were closed along with three lanes of northbound Interstate 680, according to California Highway Patrol spokesperson Office Daniel Gilmore.
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Drivers were asked to avoid the area.
No injuries were reported and fire crews were stationed on the opposite side of a highway soundwall to protect a residential neighborhood in the area, Toler said.
Bay City News contributed to this report