Euro or US? The URW Transport and Traffic series has European roadsign roots.

Clearview

FF City Street from FontFont

FF City Street Type is based on Berlin street signs.

Discussion of Clearview: http://typographi.com/000931.php

Expressway!

I just popped over to wikipedia and their is quite a few typefaces it mentions, so maybe that could be a little bit of help: http://en.wikipedia.org/wiki/Street_sign .

Bundesbahn Pi

...and slightly related, if you count signage on vehicles:

National Codes Pi

Typing “highway” into MyFonts gets 16 results.

Wayfarer

Tim

FF Info, Myriad, Frutiger, Scene, Gotham, Proxima Nova

Mikey