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Digital billboards and accident incidence: no relationship occurs
What is the statistical relationship between
digital billboards and traffic safety? Are
accidents more, less, or equally likely to
occur near digital billboards compared to
conventional billboards? To answer all these
questions, Tantala Associates conducted the
crash causation and statistical data study in
Cuyahoga County and here’s a glimpse of
this eye-opening study.
A relatively new technology in outdoor
advertising is digital billboards, which
display static messages, which, when viewed,
resemble conventional painted or printed
billboards. With digital technology, a static copy
“dwells” for typically eight seconds, and includes
no animation, flashing lights, scrolling, or
full-motion video. It is often said that the
incidence of accidents increases with digital
billboards.
Tantala Associates, a multi-disciplined,
professional, consulting-engineering firm,
conducted a crash causation and statistical data
study. The researchers conducted both a temporal
and spatial analysis of the statistics of traffic
and accident data near all seven existing digital
billboards on interstate routes in Cuyahoga
County, Ohio, in periods of 18 months before
and after the billboards were converted from
conventional to digital.
The research offers conclusive evidence that
traffic accidents are no more likely to happen in
the presence of digital billboards than in their
absence.
The purpose of this study is to examine the
relationship between certain digital billboards
and traffic safety. For this study, a study
area was identified, data was collected,
and an analysis was made of the area’s
digital billboards, traffic, and accidents.
Specifically, this study analyses the traffic
and accident data near seven existing,
digital billboards on the interstate routes
in Cuyahoga County, Ohio. These seven
billboards are located along four major,
interstate routes (I-77, I-90, I-271,
and I-480), and were converted in
July 2005 to digital billboards from
conventional billboards.
Cuyahoga County is the most populous
county in Ohio with 1.4 million people,
with a population density of 3,040 people
per land-square-mile, and with an average
age of 37. It was used as the region for this area,
because the county has multiple digital billboards
in service for more than two years in the same
market area (5% of the interstate billboards in
Cuyahoga County are digital), and the interstate
routes adjacent to these billboards are heavily
travelled (approximately 12.6 million vehiclemiles
travelled per day).
Evaluation of the relationships between the digital
billboards and traffic safety requires careful study
of the interaction of many parameters, to
include billboard characteristics (size, height,
illumination), accident characteristics (when,
where, weather conditions, contributory
causes), location and geometry, flow (traffic
volumes, frequency, speed, seasonal effects),
traffic control measures and devices, viewer
reactions (times and distances from signs).
The analysis of the study data included
two parts: a temporal analysis and a spatial
analysis. The first part, a temporal analysis,
examines the incidence of traffic accidents
at the converted digital billboards and for an
equal period of time both before and after the
conversion of the billboards. Metrics analysis
included the traffic volume, the accident rates
(APV) values and the maximum number of
accidents in any given month. Each part of
the analysis accounts for various situations
studying the results, with and without
known statistical biases, such as, bias due to
interchanges, and bias from known specific,
accident causes (for example, a deer-hit
accident as recorded in the police reports).
The second part, a spatial analysis, establishes
statistical correlation coefficients between
advertising signs and accidents along the
interstate routes in Cuyahoga County.
The results were analysed for a variety of
scenarios relating accident density to sign
density (the number of signs), to Viewer
Reaction Distance (the distance from
a billboard that the driver is potentially
within the “influence” of a billboard), and
to sign proximity (the distance from the
accident is from the nearest billboard).
The human factors study was conducted
by the Centre for Automotive Safety
Research at Virginia Tech’s Transportation
Institute (VTTI), one of the nation’s
premier research institutions on transportation
and driving performance, dedicated to the
development and dissemination of advanced
transportation knowledge. This research
concluded that driving performance measures in
the presence of digital billboards are comparable
with those associated with everyday driving.
These performance measures included eyeglance
patterns, speed maintenance and lane keeping.
The VTTI study was conducted in Cleveland,
Ohio and showed no measurable effects of
conventional billboards on eyeglance patterns,
speed maintenance or lane keeping. In the current
study, 36 drivers, unaware of the purpose of
the study, drove an instrumented vehicle on a
50-mile loop route along interstates and surface
(non-interstate) streets in Cleveland. Along the
route, participants encountered digital billboards,
conventional billboards, comparison sites (those
you might encounter in everyday driving, such
as on-premise signs located at businesses) and
baseline sites with no signs.
“The digital billboards we studied can be
considered safety-neutral in design and operations
from a human factors perspective,” according to
Dr Suzanne Lee of VTTI, the project’s principal
investigator. “The findings were consistent across
several measures.”
“The analysis and statistics in Cuyahoga County
demonstrate that digital billboards have no
statistically significant relationship with the
occurrence of accidents,” said Albert M Tantala,
PE. “Accidents are no more likely to occur near
digital billboards than on highway sections
without them.”
Eyeglance results showed no differences in the
overall glance patterns or frequency of glances
between the sites, but drivers did take longer
glances in the direction of digital billboards.
However, the mean glance length towards the
digital billboards was less than one second,
which is generally considered to be an acceptable
amount of time for a glance away from the
forward roadway.
Some participants returned for a nighttime
session to explore the potential effects of the
digital billboards at night. The findings were very
similar to the daytime results.
A comparison of accidents at the location
18 months before the digital conversion and
18 months after the digital conversion indicates
no substantial change in accident patterns.
Comparing a year before and after, the peak
number of accidents on any given month
decreased from 247 to 174, after the introduction
of the digital billboard at the location; the peak
number on any given month decreased from
14 to 8. Similar results were obtained for the
longer 36-month windows. Based on the data
and analysis, no significant change in accident
occurrences can be attributed to the conversion
of these billboards to digital format. It should
also be noted that the winter months had more
snowfall in the 18 months prior to the conversion.
For these billboards, the results suggest that
digital billboards in and of themselves have no
influence on the occurrence of traffic accidents.
The temporal comparison also suggests that
digital billboards are no more likely to increase or
decrease the accident frequency than conventional
billboards, or than stretches of the interstate
routes with no billboards.
Both studies were commissioned by the
Foundation for Outdoor Advertising Research
and Education (FOARE), which supports
research and provides an educational forum
and structure to assess new and emerging
issues related to the outdoor advertising
industry. “The industry and the public needed
a targeted, empirical assessment to determine if
digital billboards impact driver performance,”
said FOARE chairman Paul Cook. “FOARE
undertook these studies because no other
government or private research exists that
specifically examines a cause and effect link
between outdoor digital billboards and driver
behaviour.”
For more info, visit
www.tantala.com
