Carpooling points incentive
If there are two or more active waze clients in the same car, then you should get a points multiplier, perhaps 2x. This would give wazers an incentive to carpool and help reduce the number of cars on the road. It could also help waze improve the quality of it's GPS recording, since they would be able to average the two different GPS receivers from each phone.
there would need to be logic to recognize one car is not 'increased traffic' in the lane
GPS polling would need be reduced for those vehicles not capable of accommodating multiple charging leads.
It would be simpler for those not fond of personal transportation to cherish their respective warm-fuzzy for carpooling :P