Oops!

It appears that the State Highway Departments of Missouri and Illinois don't talk to each other. Check out the Google satellite picture of the bridge at Alton that crosses the Mississippi.

A FWIW update - This cable stay bridge replaced an old 2 lane truss style that had been there since the 20s. There was a documentary about the construction of it a few years back on TLC or History channel or one of those manly-type channels. It was pretty interesting.