It happened just after 4 a.m. on the North Freeway northbound at Mt. Houston.
Investigators say a pick-up truck rear-ended the ladder truck.
The truck was being used to block off lanes of the freeway as investigators worked to clear a different accident when the truck was rear-ended.
Four firefighters were in the truck at the time of the crash. No one was hurt.
Police shut down a portion of I-45 while they worked to clear the scene. It reopened at 6:30 a.m.
Investigators found drugs and a weapon in the pick-up. The driver is being taken in for testing to determine if he was under the influence at the time of the crash.
A sergeant on the scene said the fire truck is worth about $300,000. It's not clear yet if the truck was totaled in the crash.
Eyewitness News reporter Pooja Lodhia is on the scene and has continuing updates on ABC13.
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