Making a car only go straight no left or right

How do I make so a car only goes forward and doesn't automatically steer left nor right?

I'm trying to do a crash test with the Nardelli crash test car.

 

Switch to the Nardelli cart, revv it up, put in gear & then moment you do that, pause the physics (J key). Switch back to the other car, unpause physics & watch the cart ram into it

 

You can also set it to chase that way it will always hit it.

 

There is no way to make a car go truly straight. It will always have some slight pull. Although like the others said you can either just hold down the gas or put the AI to chase mode.