>
>I think that the radial velocity as a vehicle goes around any turn is
>zero.
>(as if there were a string from the vehicle to the center point of the
>turn)

Hmm. Don't think so. Most road curves are not arcs of circles.

>A microwave doppler radar could be used to detect radial (side looking)
>velocity.  The radar would see through the ice and still work fine.

This is getting some high cost solutions. How about a (slightly damped)
magnetic pendulum and a couple of hall effect sensors. A PIC could monitor
the pendulum position and calculate acceleration from it. Add a simple
steering wheel sensor and look for big deviations between chosen direction
(from steering) and actual direction (from accelerometer).

Keith.
==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: kdowsett@rpms.ac.uk
WWW:    http://kd.rpms.ac.uk/index.html