A unit that begins its movement phase inside a vehicle can get out either before or after the vehicle has moved. When the unit disembarks the models are deployed within 2" of the vehicle. If the vehicle has already moved then the infantry cannot move other than to deploy, and they cannot disembark if the vehicle moved more than 12". If the vehicle has not yet moved the infantry may move as normal after disembarking, the vehicle can then move off separately at any speed.
Troops onboard a vehicle may not disembark in the assault phase.
Diagram: Disembarking Before Vehicle Moves. The vehicle did not move before the troops disembarked, so both the vehicle and the troops can move as normal after the unit has deployed.
Diagram: Disembarking After Vehicle Moves. As the vehicle moved before the troops disembarked they can only be deployed if the vehicle moved less than 12" (deploying within 2" of the vehicle). The vehicle cannot be moved any further this turn.