The high-speed crash happened around 10:45 p.m. Thursday along the Highway 249 feeder at the Grand Parkway.
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Deputies say the driver of a Chevy Silverado was towing the horses in the trailer when he slammed into a utility pole.
The horses died on impact.
The driver was flown to Memorial Hermann Hospital with life-threatening injuries. He's in critical condition.
Investigators believe the driver wasn't just speeding, but that he also may have been drinking after finding alcohol in the truck.
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"Investigators went to the hospital, found signs of impairment. He appeared to be intoxicated. Inside the Chevy, we did find at least one glass container containing alcohol, so we are investigating this as a DWI crash, if the driver survives," said Harris County Sheriff's Office Sgt. Simon Cheng.
Investigators plan to pursue animal cruelty charges for the deaths of the horses.
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