The Hitcher 2

Fifteen years after surviving the events of The Hitcher, Jim Halsey (C. Thomas Howell) now works as a police officer. He has recently been suspended for using excessive force on a kidnapping suspect, and decides to visit retired Captain Esteridge in Texas to talk about his lingering mental issues on what happened to him. Jim's girlfriend, Maggie (Kari Wuhrer), is unaware of Jim's past and pleads to come along.
The couple arrive in Texas, and pick up a car Esteridge left for them to drive to his house. The drive on the lonely road triggers Jim's PTSD, and when they see an RV that has been run off the road, blood dripping through the door, Jim refuses to stop and help. Soon, a motorcycle speeds past them and crashes. The driver is seemingly all right, and Maggie insists they take him on board. The Hitcher (Jake Busey) is insistent on making small talk and joking with them, but Jim is overwhelmed and evicts him from the car.
Jim and Maggie continue their journey. They are eventually pulled over by a cop, but have been also followed by the Hitcher, who has hijacked an 18-wheeler truck and killed its driver. The Hitcher shoots the cop and tries to grab Jim and Maggie but is successfully thrown off the car when they escape.
The couple arrive at the Esteridge residence late at night, but the Captain and his wife have been killed by the Hitcher. Jim and Maggie find themselves caught in a shootout between the Hitcher, who is in the hayloft of the barn, and the local police, who have arrived on the scene. During the melee Jim pushes Maggie out harm's way and is shot by the Hitcher. Maggie manages to escape in her car, but Jim dies, his last words being to tell her to kill the Hitcher.
Maggie falls asleep in the desert. When she wakes up she is knocked unconscious and put inside an abandoned water tower that is on the verge of collapsing. The Hitcher taunts her and then leaves, but Maggie manages to escape and use the 18-wheeler from earlier in the film to get away. She arrives at a gas station, makes a phone call and cleans up, but the Hitcher has followed her and killed the clerk. The Hitcher intends to frame Maggie for all the killings that have happened, and as part of this plan cuts off his own finger. The police arrive at the gas station. The Hitcher spins his story and Maggie is arrested. She is transported by the sheriff's van, but during the journey the vehicle is knocked on its side by an excavator. The Hitcher kills all the police officers of the escort, and tosses the key and a revolver to Maggie to make it look like she killed all of them.
Maggie and the Hitcher have a final showdown, where the Hitcher drives a stolen tanker truck and Maggie pilots a mail carrier plane from a nearby airfield (she is shown to have a crop dusting business earlier in the film). Maggie kamikazes the plane into the truck, but manages to escape the ensuing explosion. Maggie finds the unconscious Hitcher and ties him to the truck. When he wakes up, realizing he is trapped, pleas for mercy. Maggie ignoring his pleas and prepares to finish him.
But before Maggie can execute him, the police show up again. Knowing that his could be his only chance for escape, the Hitcher yells that Maggie is trying to kill him. The police believe him and they free the Hitcher and shoot Maggie in the leg as she attempts to enter the truck's cab. Once free, the Hitcher kills the cops. Maggie manages to make a safe distance away and shoot the tanker, which explodes and kills the Hitcher. The film then ends with Maggie dropping the shotgun to the ground and standing in the road facing the remains of the burning truck.

Question: What knocks over the sheriff's van that is carrying Maggie?
Answer: Excavator