A small device embedded in a car's dashboard that monitors events such as: - Anti-lock brakes or traction control kicking in (slippery road conditions) - Drastic changes in temperature/humidity (potential for ice, fog, or whatever) - Current speed (traffic flow)

and uploads this data, along with GPS coordinates, to a central server via cell phone data link or WiMax or something. Aggregate data about traffic speed and weather conditions nearby could be sent out to subscribers for display on an in-dash device:

"Hey, I see that 1.3 miles ahead on Hwy 494 three cars reported traction control kicking in within the last 20 minutes. Be careful!"

Getting manufacturers' cooperation for hooking into the cars' computers would be really tough. But the technology is perfectly feasible.