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JEFFERSON COUNTY, Colo. — Two people were killed in a fiery crash involving a semitruck and four other vehicles on C-470 in Jefferson County on Thursday morning, the Colorado State Patrol said.

The crash happened about 11 a.m. in the westbound lanes between West Ken Caryl Avenue and West Bowles Avenue.

The Colorado State Patrol said the semitruck was going eastbound when it crossed the median and went into the westbound lanes where it hit another vehicle.

The semitruck, which was hauling sand, went through two metal barriers and hit a concrete wall before the cab and the other vehicle underneath it landed on a bike path about 30 feet below the highway. Both then both caught fire.

Flames and heavy smoke could be seen at the crash scene and firefighters were able to extinguish a small grass fire.

Four other vehicles, including a motorcycle, were hit by debris. The motorcyclist suffered a minor thumb injury, but there were no other reported injuries, the Colorado State Patrol said.

Both directions of C-470 were closed between South Kipling Parkway and Highway 285.

Eastbound lanes reopened just after 2 p.m. Westbound lanes reopened shortly before 7 p.m.

The Colorado Department of Transportation said an average of about 67,000 vehicles travel that portion of C-470 each day.

The bike path will remain closed until further notice. The cause of the crash is under investigation.

The stretch of C-470 where the crash happened has several safety barriers. Cable barriers line much of the median.

Studies from other states and the federal government show they can prevent up to 95% of vehicles from crossing the median.

They don’t work as well when vehicles are traveling faster than 62 mph.

Also, the barriers might not prevent semitrucks, especially those loaded with sand and driving downhill at highway speeds, from crossing a median, according to highway experts.

Plus, the cable barriers need space to flex.

In the median where the truck crashed, there’s a sign, so the Colorado Department of Transportation installed metal guardrails. The semitruck crashed through two of them.

“Sometimes you’re just dealing with these very peculiar situations, with a very heavy truck moving at a very high rate of speed,” AAA Colorado’s Skyler McKinley said.

The truck also crashed through a concrete wall that’s about 40 inches tall on the side of the highway before falling off an embankment.

“There are a million scenarios you could run though,” CDOT chief engineer Josh Laipply said. “It kind of depends on how directly they’re approaching it (the barrier). If they aim straight for it, then probably not.”