Communicating new speed limits via signage and markings is essential for effectively managing speeds. Laws and policies about where speed limit signs should be placed vary from city to city. Placing identical speed limit signs on every block of a corridor where the speed limit never changes is costly and does not have proven speed-management benefits. However, preliminary studies out of Seattle show that increasing sign density to one sign every 1/4 mile from one sign every mile does result in lower speeds and fewer crashes. At a minimum, cities should follow the guidance below about speed limit signs, making specific decisions about sign density and placement based on local context.
Cities with default speed limits or category speed limits should post “Speed Limit X Unless Otherwise Posted” signs at gateways into the city: highway off-ramps before an intersection, major streets at city limits, bridge and tunnel entrances, ferry terminals, and airport car rental facilities. Signs should be placed on any street that diverts from that default limit.
Cities with slow zones should post the limit for that zone at gateways into the designated area. On-street markings can also be utilized at the points where the speed limit changes or at key entrances to slow zones.
Cities with major arterial slow zones and high-crash corridors can post signs on those streets to reinforce the importance of adhering to the speed limit.