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Speed Feedback Signs as a Tool to Manage Demand for Lower Residential Speeds


Citizens frequently express concerns regarding unsafe speed and look for ways to improve speed
compliance. Speeding is a subjective term since a vehicle may be driving within the posted speed
limit but may still be inappropriate for the road conditions. In an urban environment, speeding in
residential areas, schools and playgrounds is a common concern. Although there are number of
tools such as: posted speed limits, signage, electronic speed warning signs, enforcement etc.
available to deter speeding drivers, addressing these concerns in a long lasting way has always
been a great challenge to transportation professionals.
Vehicle activated traffic calming signs have been used in Canada for over a decade. In Calgary,
Speed Limit Observation and Warning System (SLOWS) and Interactive Speed Limit
Observation and Warning System (iSLOWS) have been used in residential neighbourhoods,
school & playground zones, construction zones, and special events such as Calgary Stampede to
educate drivers against speeding. Although these two devices look strikingly similar in function,
the process to assign these devices is completely different. SLOWS trailers are temporary and
rotated on a 2-week/location basis following a citizen request whereas iSLOWS are permanently
assigned to a location following a detailed traffic speed study. Amidst the increasing demand and
popularity of these devices as tools to address speeding concerns in short term, long lasting
impacts of these devices on educating drivers against speeding remain questionable.
The City of Calgary conducted speed study at various locations in 2014 with the objective of
evaluating the effectiveness of SLOWS trailers and iSLOWS in reducing speed. Speed display
boards mounted on trailers were placed on roadside at various playground and non-playground
zone locations for a period of 2 weeks. Speed data were collected before, during and after the
installations using rubber road tubes connected to an automatic counter in the immediate vicinity
of the speed display board. In case of iSLOWS, the speed data were collected in different trigger
speeds to see the impacts of the speed limit warning sign to drivers.
Results indicated that average speed during SLOWS trailer deployment reduced by 1.59 km/h to
5.64 km/h depending on the location, compared to before installation period. These results were
significantly different at 95% confidence level at most locations. Results from iSLOWS study
indicated that the level of speeding reduced when the trigger speed is lowered from 35 km/h to
30 km/h. However, the positive effect didn’t last long as the speed level was back to the before
installation level after 4 weeks of iSLOWS installation.

Conference Paper Details

Session title:
Responding to the Safety Needs and Expectations of Residents and other Road Users (Non-motorists)
Churchill, A.E.
Mishra, S.
Road safety