[who_would_fardels_bear]

If the cars are designed properly then they will depend on a map and pics stored locally in the car plus the best estimate of their location using their last GPS coordinate and the record of the speed and direction of travel. The map will be updated on a regular basis via satellite, but the car won't depend on it.

I believe they should be able to record the speed of the vehicle very accurately. However, I wonder about the direction. If they have an internal compass that includes magnetic declination, then great. Otherwise they will need to depend on the pics, radar, and lidar to finetune their location within the roadway.

[CurlyDave]

...If they have an internal compass that includes magnetic declination, then great. Otherwise they will need to depend on the pics, radar, and lidar to finetune their location within the roadway...

A ring laser gyro or fiber optic gyro would allow traveling many miles by dead reckoning. I don't think cost is an issue, if someone makes millions of them the costs will come down.