car harness/restraint for older child

[Unregistered]

My autistic son is 14yo, 59 in. and 128 pounds.
He becomes very challenging in the car when
he gets angry. He has reached for the steering
wheel, thrown things at me, hit and pulled
hair, and opened the car door. This has all happened
while we were on the highway.
I need something that he can't get out of.
We have tried something similar to the EZ-vest
on the bus, but he can get out of it in seconds.
We finally had to measure him for a humane restraint.
That helps on the bus, but I am wondering what
is out there for cars.
Any ideas?
Thanks,
Silvia

[Jennifer mom to my 7]

Did you try the vest that zips up the back? http://www.ezonpro.com/products/familyVehicle/adjustableVest/103z.shtml