Then why tie the hands? You would not hesitate to drive if you thought it would save your family. You don't need to be tied. Which brings up the question as to why tying the hands to the wheel forces you drive to the designated target? It may keep you in the car, but it doesn't prevent you from going anywhere other than the target. It sure does prevent you from putting the car into gear so you can drive though. This story smells like a dead camel.
If the bomb was on a timer he may as well go through with it.
The story maybe a farce however MEMRI is usually reliable.
I would think the bomb would be remotely triggered, which would mean a delay in detonation, maybe they were worried he would run or perhaps try to disable the bomb.
I can see many reasons to tie a unwilling drivers hand to the wheel and all you have to do is put the car in drive for him and follow at a distance to use the trigger device.