A recreational vehicle caught fire on the Blue Route sometime shortly after 1 p.m., causing a shutdown of the highway heading south near the interchange with Interstate 76 for about two hours, state police said.
By 4 p.m., one southbound lane of Interstate 476 was reopened, state police said, but traffic in the area of I-476 at Old Gulph Road remained swamped.
It remains unclear how the RV caught fire and a state trooper at Philadelphia's Troop K barracks said she did not know when exactly the fire began.
Further south, a state Department of Transportation traffic camera set up on I-476 south of County Line Road showed no vehicles driving on the southbound side while northbound traffic slowed heading into the area of the RV blaze.
State police did not know when the southbound lanes would reopen.