Although they don't receive nearly as much press as bombings, vehicular ambushes are quite common in Israel.
The classic way to conduct such an ambush is by blocking the road. Roadblocks are a surprise that's sprung so that the driver of the targeted vehicle instinctively hits the brakes and is instantly a victim of tunnel vision. Once the target vehicle is stopped, the terrorists swarm it, killing or kidnapping the driver and passengers.
Terrorist roadblocks are often constructed out of whatever is at hand that can be rolled, pushed, or propelled into the road to effectively block the path of an oncoming vehicle. In Israel the terrorists use trucked-in boulders. I expect that terrorists in the United States would fell trees for roadblocks.
Vehicles, both stationary and moving, are also used as roadblocks.
A stationary vehicle can be driven into the road perpendicular to and totally blocking the path of the targeted vehicle.
Moving vehicles can be used to hem in the target. Basketball fans can probably relate to this as a "Moving Pick" roadblock. It works like this: An attack vehicle passes the targeted vehicle on the right shoulder of the road, then swerves left, stopping in the path of the targeted vehicle blocking its path. Sometimes another vehicle will also block the target's rear, preventing the victim's escape.