Short-term priority: public pressure to enforce existing laws and regulations to remove "gross polluting" cars from the public roads.
Middle-term priority: design a "hub to hub" bus service from outlying communities to selected "hubs" in the Fresno-Clovis area. Some examples: RiverPark, Fashion Fair, downtown, Manchester Center, Fresno State, Fresno Pacific University and Saint Agnes Hospital. Persons using the service to go to and from work would have a special pass to reduce the fare. Initially the rides would be free to build clientele.
This will not work unless park-and-ride areas are built in the outlying communities and the buses operate on a low pollution fuel. Propane? Electric? Some combination?
Long term (if you thought the middle priority was expensive, now you will really see the costs of clean air go up): Eliminate all intrastate trucking between major population areas. Instead the transport trailers would be hauled to hub centers where they would be loaded on railroad cars and moved to destination cities by electric locomotives. The truck tractors needed to move these loads the shorter distances within the hub centers would also be fuel-efficient engines that can shut down at delivery sites rather than the continuously running diesels of today. Has anybody noted that United Parcel Service trucks are shut down during deliveries?