http://schema.org/Car
http://schema.org/Vehicle
A substantial and detailed proposal has been prepared by Martin Hepp, see associated pull request: #80
Announcement / discussion: http://lists.w3.org/Archives/Public/public-vocabs/2014Dec/0057.html
Original W3C wiki link https://www.w3.org/wiki/WebSchemas/Vehicles
See 2015-01-09 review from @tmarshbing which suggests amongst other things partitioning the proposal into smaller sections.
See also #263 for the property-value proposal, which supports the proposal.