A massive fire on Monday caused falsework at a freeway interchange project to collapse onto Interstate 15 in Hesperia, Calif., northeast of Los Angeles. The fire and subsequent cleanup shut the freeway down and cut off the main link between Las Vegas and L.A. and caused 20-mile traffic backups that some motorists were trapped in for more than six hours, according to local media reports.

However, just before the freeway was closed, one daring motorist snapped this photo and tweeted it to Caltrans while driving below the blazing wood forms on the six-lane overpass:

The formwork for the I-15 Ranchero Road Overpass project had been substantially interlaced with rebar when the fire broke out, but concrete hadn't yet been poured. The blaze was caused by a welder who was cutting rebar, according to San Bernardino Associated Governments (SANBAG), the lead agency funding the project. Winds were reportedly 20 mph at the time the wooden forms were ignited. No serious injuries were reported. 

The fire burned through the night aided by the wind, but is now out and crews are in the process of cleaning up the site. However, due to the amount of tangled rebar in the wreckage, demolition is very difficult, said Raymond Wolfe, SANBAG executive director, at a press conference.

Raw footage of the formwork during the fire. Courtesy of DailyVideoNews

The $59-million interchange is being constructed under a $31.7-million low-bid contract by Security Paving Co., Sun Valley, Calif. Construction began in January 2013 and was expected to wrap up in spring 2015. Project officials with Caltrans and other partner agencies have told local media they expect the fire to cause a six-month delay and add millions of dollars to the project cost, though exact estimates are still pending the cleanup.

Currently, the northbound lanes have been cleared and Caltrans is assessing the condition of the interstate and conducting any repairs to the pavement . Officials hope to open the northbound lanes this evening, and the southbound lanes sometime tomorrow.

The project is being built to connect Mariposa and Caliente roads to I-15 via a full-service interchange. The Ranchero Road overpass was designed to carry three through lanes in each direction along with additional turn lanes at the freeway ramp connections.