12th Street (including East 12th Street) runs East/West(-ish) from West Oakland, around the southern end of Lake Merritt, and then parallel to International Blvd. until it ends just past 54th Avenue. 

The portion on the southern end of Lake Merritt from Lakeshore Drive to 1st Avenue was originally built upon the 12th Street Dam, and what was then known as the Frickstad Viaduct from the early 1950s to about 2011 was the home of the famous Southerly/Northerly signs. This section is now officially known as Lake Merritt Boulevard

The portion of 12th Street from Lake Merritt Boulevard to Market Street is used for one-way traffic westbound.