You can see above how vehicular sensor networks (VSNs) can be built on top of Vehicular Ad-hoc Networks (VANET) by equipping vehicles with onboard sensing devices. You'll find more details by looking at MobEyes research project.

This is one of the projects handled by the Network Research Lab at UCLA Computer Science Department, where computer science professor Mario Gerla and researcher Giovanni Pau are trying to turn your cars into wireless networking nodes.