Studies have shown that speed zoning has very little permanent effect on average vehicular speeds. There are indications, however, that it does have a tendency to group more of the drivers within the pace since some of the slower drivers speed up and some of the faster drivers slow down after the speed limits are posted.
Federal Highway Administration research confirms MassHwy’s observations regarding the “very little permanent effect” of posted speed limits on average vehicular speeds: “State or local officials often receive citizen requests for speed limit reductions because of perceived excessive speeds. However, research has repeatedly shown that changes in posted speeds have little effect on operating speeds.” Parker, M.R., “Synthesis of Speed Zoning Practices,” Report No. FHWA/RD-85/096 (1985).