LEGO released a City Accessory Pack (40170) last year and now it looks to follow up with this new expansion pack that is specifically for vehicles.
The LEGO City Vehicle Expansion Pack (40303) provides some nifty add ons of existing vehicles like the red pick up truck from the LEGO City Pickup And Caravan (60182) set or the police boat from the LEGO City Wild River Escape (60176).
The add-ons actually can be attached to a multitude of other vehicles and the pack basically provides you with a bunch of elements that you can mix and match with however you like.
It has 79pcs in all and there is no word how they will be distributed. Most likely through a gift with purchase further down the road.