2012-06TS
Published May 2012
Impacts of Playground Warning Signs
on Vehicle Speeds
What Was the Need?
TECHNICAL
SUMMARY
Technical Liaison:
Amy Marohn, City of Bloomington
[email protected]
Project Coordinator:
Shirlee Sherkow, MnDOT
[email protected]
Principal Investigators:
John Hourdos, University of Minnesota
Gary Davis, University of Minnesota
Keith Knapp, Iowa State University
LRRB PROJECT COST:
$79,647
The yellow signs that warn drivers about nearby playgrounds are intended to alert drivers to slow down and
watch more vigilantly for children and other pedestrians.
Residents often request these warning signs from their
local governments to make their neighborhood streets
safer, but there has been little research to demonstrate the
signs’ effectiveness.
Agencies aim to install only the most necessary road
signs. If too many signs are installed, drivers may pay
less attention to all of them, or they may rely too heavily
on signs to warn them of potential hazards. In addition,
recent Federal Highway Administration regulations will
require all signs to meet new minimum retroreflectivity standards, which means signs must be replaced more
regularly than was required in the past at greater cost to
taxpayers. Limiting the number of signs can lower the
costs of complying with the new law.
Researchers found that
playground warning signs
did not cause drivers to
significantly reduce their
speeds, but drivers did slow
down when playgrounds
were busy and parked cars
lined the street. These
results can help local
agencies evaluate the
installation of these signs.
In responding to residents’ requests for playground warning signs, city and county
engineers must weigh these factors against the signs’ potential benefits. Research was
needed to investigate whether playground warning signs are effective at getting drivers
to slow down.
What Was Our Goal?
This project’s objective was to evaluate the impact of playground warning signs on
vehicle speeds at three locations in Bloomington, Minnesota. Since the state and federal
editions of the Manual on Uniform Traffic Control Devices currently leave the placement of these signs to engineering judgment, the study results would help local engineers determine whether the benefits of the signs justify the costs.
What Did We Do?
According to state and federal
rules, playground warning signs
can be installed as needed based
on engineering judgment.
RESEARCH
SERVICES
Investigators performed a literature review of related research, including studies of
how vehicle speed relates to crashes and to pedestrian fatalities, and studies that address the speed and safety impacts of warning signs. Next, researchers reviewed 13
candidate study sites near playgrounds along residential streets in Bloomington. They
selected three sites for collection of vehicle speed data before and after the installation
of playground warning signs.
Three types of data at each study site were collected one month before a pair of the
signs was installed and one week to one month after installation. Researchers used a
pneumatic tube device to measure vehicle speeds. Since drivers might tend to slow
down when children are visible at a playground or when cars are parked on the street,
researchers also recorded data on playground activity levels and the presence of parked
cars. Then they used linear regression analysis to estimate the change in average vehicle speed associated with the presence of the playground warning signs, controlling
for the effects of varying amounts of playground activity and parked cars.
O F F I C E O F P O L I C Y A N A LY S I S ,
R E SE A R C H & I N N OVAT I O N
continued
“We found that actual
playground activity is a
much stronger indicator
to drivers to be attentive
than playground warning
signs. This study gives
local engineers
quantifiable measures
of the signs’ impact to
reference as they make
decisions about sign
installation.”
—John Hourdos,
Director, Minnesota
Traffic Observatory,
University of Minnesota
“In Bloomington, we’ll
use this study as support
for our current standard
practice of not
installing playground
warning signs. The speed
reductions achieved were
not significant enough
to justify installing them
unless other unique
conditions are present.”
—Amy Marohn,
Civil Engineer—Traffic,
City of Bloomington
Produced by CTC & Associates for:
Minnesota Department
of Transportation Research Services
MS 330, First Floor
395 John Ireland Blvd.
St. Paul, MN 55155-1899
(651) 366-3780
www.research.dot.state.mn.us
Investigators gathered data at three sites in Bloomington, including this park on Colorado
Avenue South, which is adjacent to an elementary school. At this site, researchers found no
difference between vehicle speeds recorded before and after playground warning signs were
installed.
What Did We Learn?
Installing playground warning signs did not have a large effect on average vehicle
speeds at any of the three sites. At one site, the signs had no measurable effect, while
signs at the other two sites led drivers to reduce their speeds by 0.9 mph and 1.5 mph
on average.
However, researchers found that vehicle speeds were strongly related to levels of playground activity and parked cars. At one site, vehicles drove an average of 10 to
15 mph slower when playgrounds were busy, which appeared to be related to the
greater number of cars parked along the street.
The impact of playground warning signs on vehicle speeds appeared to be site-specific.
Researchers noted that some of the variability in the vehicle speed impacts is likely due
to the differences in site characteristics and suggested that it may also be affected by
subjective differences in how the field personnel categorized on-street parking levels
for the study.
What’s Next?
City and county engineers can use this research in their decision-making process when
they consider whether to install playground warning signs. This study fills a gap in
research on this topic, and serves as a timely, credible reference for engineers as they
review their sign management policies in light of the new retroreflectivity requirements.
To help local engineers make decisions about signage as they comply with the new
requirements, the Local Road Research Board recently produced a handbook on sign
maintenance and management. A follow-up research project, “Best Practices for Sign
Reduction on the Local System,” is expected to be complete in 2012.
This Technical Summary pertains to the LRRB-produced Report 2012-06, “Vehicle Speed Impacts of
Occasional Hazard (Playground) Warning Signs,” published February 2012. The full report can be
accessed at http://www.lrrb.org/PDF/201206.pdf.