Police are investigating why the driver of an 18-wheeler drove off a bridge late Sunday, his cab landing in a highway median below.

First responders were sent to the scene about 10:20 p.m. They found that an 18-wheeler had fallen off the Iron Horse Boulevard bridge and landed on the median of Northeast Loop 820.

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The driver was extricated from the 18-wheeler and airlifted to John Peter Smith Hospital in critical condition.

North Richland Hills police were still investigating the crash Monday morning.

The Texas Department of Transportation expected the left lane of westbound 820 and the Iron Horse TEXpress lane to be closed through the afternoon.