Salt Lake City marks part of the downtown and residential areas for 20mph speed limits for motor vehicles

Typically, the lowest typical speed limit in most center cities is about 30mph. DC is an outlier with a 25mph prevailing speed limit. While I have seen neighborhood streets in Chevy Chase, Maryland signed with a 20mph limit (see this blog entry, "20 mph speed limit sign on Stanford Street at East Ave in the Town of Chevy Chase, Maryland," from 2010), Salt Lake City is the first major city where I've noticed 20mph speed limits on arterials, not just on neighborhood streets.