Carpool lanes, discounts, other perks Clean Air Vehicle (CAV) decals In Calfornia, you can get the white "zero emissions" sticker, costs you $8. Basically, California law allows a solo driver to drive in a standard carpool lane, i.e. "diamond" lane. You place the small decal on the right side of the rear bumper. The large decals are supposed to be on the rear quarter panels, behind the rear wheel. As anyone can see, there's really no room there. Would be nice to get a ruling from the DMV on this. Note that you should have a "decal ID card" to prove the decals are yours, keep with your car registration. Where can I drive? Well, that is an interesting question. So, first, you can drive in the "normal" carpool lanes, i.e. diamond lanes. But you can also qualify for one of the "transponders" that has a switch, to indicate one, two, or three occupants. Effective February 24, 2014, vehicles displaying a DMV issued White or Green Clean Air Vehicle Decal will be toll-free. All vehicles, including Clean Air Vehicles, are required to have a FasTrak® transponder while traveling on the ExpressLanes. To ensure toll-free travel, set your transponder to switch position 3 (3+ person carpool) prior to starting your trip. Clean energy vehicles that do not have a Clean Air Vehicle Decal must drive with their transponder set according to their vehicle occupancy. (I believe this only applies to the "ExpressLanes" in LA, Orange, and San Diego counties. In LA this appears to be the I-110 and I-10 freeways. In San Diego, I think this is the I-15, but need clarification. I found this: "Note that ridesharing is lways FREE on the I-15 Express Lanes. As long as two or more people are in your car, you can enjoy the time-saving benefits of the I-15 Express Lanes at no cost. Simply remove the transponder from your windshield, and place it in the Mylar® bag provided with your transponder. This will prevent your transponder from being read by the FasTrak tolling system and will ensure you aren’t charged the toll." So does the San Diego system not use a switchable transponder? Reading the above seems to indicate that if you don't have a transponder, you are not charged... so how do they know if you are cheating?