Safety Impacts of Traffic Calming Measures (U.S. Experience)
No. Avg. Annual Collisions Sig.
Measure Sites Before After Change Level
12’Humps 50 2.6 2.3 -13% .40
14’ Humps 5 4.4 2.6 -40% .18
22’ Tables 8 6.7 3.7 -45% <.01
Circles w/o Seattle 17 5.9 4.2 -28% .04
All Circles 130 2.2 0.6 -71% <.01
Overall 163 2.5 1.2 -51% <.01
exclude Seattle 80 3.8 2.7 -25% <.01