Google has redesigned the Transit Layer in Google Maps. Until now Google had placed the transit information on top of the base map tiles. With this redesign Google has now changed the entire base map to put more focus on the transit lines, and lower the prominence of roads.
The result is a much cleaner look and the transit lines now do not completely obscure the roads underneath.
If you want to see which cities have public transit click here.
Via: Google LatLong