It was only on September 15, 1991 that a freeway viaduct around the town of Wallace moved Interstate 90 off of surface streets, finally putting an end to the last stoplight still in use on a transcontinental interstate. Wallace is located in what state, one of only two in which I-90 runs for a distance of less than 100 miles, also home to the most northerly point on I-90, in the town of Post Falls?
IDAHO