My barrier collision simulation terminates with the vehicle still engaged with the barrier. Why?

It sounds that your vehicle's velocity has reached the Linear Velocity termination condition set in the Event's Simulation Controls dialog.  By default this value is set at 2 mph, so when your vehicle's velocity reaches a value less than 2 mph, the event stops.  This may appear that the vehicle does not rebound from barrier, however a simple change to the termination conditions will allow the simulation to continue.  On the menu, select Options, Simulation Controls and then set the value for Linear Velocity to 0 mph, thereby overriding the velocity termination condition.  Reset and run the event and you will now see your vehicle fully engage the barrier and rebound as expected.