It happened shortly after 1:00 p.m. at the intersection of Bristol and Mearns roads in Warminster.
The US Postal Service tractor trailer was turning, as a Chevy Impala entered into the intersection.
A witness told police that the car turned on a red light. Upon turning, the vehicle got stuck underneath the truck.
Three people inside the Chevy Impala were taken to Abington Memorial Hospital in stable condition.
The driver of the tractor trailer was unhurt.
The intersection was closed for approximately 2 hours, but has been reopened.
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