Must mean something different where you are! Up here in the bay area, it's only for crossing bridges! The only way you can use a diamond lane up here is if you meet the standards for having high occupancy in your car, or if you have a hybrid with the appropriate sticker.
We have one FasTrak registered fo all 3 of our vehicles, so whoever is going across the bridge takes it with them. There are special FasTrak lanes at the bridges so we can pretty much sail through. BART also has an electronic card that you just tap on the appropriate location on the turnstile and walk in. Both are automatically rechargeable, so no one has to worry about not having appropriate change with them. Very handy.
