I saw the arch on a Brit TV programme recently, where the comedian/traveller Billy Connolly travelled the entire length of Route 66, and St Louis received a lot of coverage.
You can find it quite easily on youtube, Rap, if you're interested.
Quite informative and very funny on occasions. In the arch section, he's looking out from the viewing window and, working out where the sun is, he tries to locate a landmark in the city, but with no luck.
A fellow tourist lets him know he's looking in completely the opposite direction. Some expert explorer indeed. Hilarious.