§The speed of traffic is
self-regulating. The number on the sign has no appreciable effect on average speeds or 85th percentile speeds,
but it can affect behavior and improve flow management,
resulting in fewer flow conflicts and lower
accident rates.
§Whereas under posted
limits result in greater flow friction and conflicts, to the detriment of safety.
§Roadway design and environment determine safety and travel speeds, not the number on the sign.
More importantly, a road with a posted limit is not necessarily safer than a road without posted limits.
§Traffic calming has it own short comings and many treatments can
increase accidents, reduce roadway capacity, increase
air pollution and lose their novelty effect as those
that use the roadway daily return the speeds they are comfortable with.