Sometimes even Google makes mistakes. The new version of the desktop Google Maps has an updated interface for layers like traffic, transit, bicycling and terrain. If you enable the traffic layer, Google shows a legend at the bottom of the page and claims that red = fast-moving cars and green = slow-moving cars. Obviously, the labels are reversed.
Here's the previous interface, which uses the proper labels:
This mistake was spotted by Ken Drori, a reader of this blog. Fortunately, it's quite easy to fix.