Praise be to Allah.
We put this question to Shaykh ‘Abd al-Rahmaan ibn Jibreen (may Allaah preserve him) and he answered as follows:
They are considered to be waqfs, hence the people who donated them are not allowed to ask for them to be returned.
You have donated this car or this vehicle to transfer students or to transfer the dead, so you do not have the right to take it back. Your reward will be ongoing so long as use is made of the object.