In a fairly straight line and in good weather? Very fast (compared to current US highways). 150 mph or more.<p>The primary factor I can think of in terms of risk, are wild animals crossing and vehicle malfunction (eg tire rupture). Censors&#x2F;radar, both in the vehicle and along the perimeter, should take care of the animal threat. On the mechanical side, well, the goal would be to get the rate of death down to perhaps airline-like numbers.