The Smithsonian National Museum of American History has an on-line exhibit called America on the Move. Most of the activities are not geared toward kindergarten students, but there are some cool images, games and lesson plans that could serve as jumping off points for more ideas.
An easy-to-read printable book called "Go Car Go!" is available from DLTK.
Mrs. Nelson has a lot of great ideas for her transportation unit.
Ecole Whitehorse Elementary has more links than you can shake your tailpipe at including a nice list of learning objectives.
More good stuff on lessonplanspage.com.