While I love this hobby, and would be the last to stifle experimentation :
The absolute last thing I would do is give my car pc control of the vehicles rate of speed :-) Call me "old fasioned" but we all have seen those "that just cant be ?" moments when dealing with pc's and code where some extremely simple thing, which absolutely functions every time you use it, returns a value that is "wrong?".
I dont know what you are driving, but it would significantly effect the outcome of a "glitch".
In my "city car", a 95 Honda Civic with 4 cylinders that has a zero to 60 mph time of about three minutes (its so low its embarrassing when getting on the highway), if it decided that I should be doing 100 mph, I would have plenty of time to say "wtf?" and shut it off.
In the vette, if I was doing 60 and it decided I should be doing 100, I'd be doing 100 in less than four seconds.
GPS . . .great, where is a gas station . . .great, is it gonna rain . . .great, control of the accelerator . . .? . . .nah, Ill keep that one. Thanks