This article pertains to motorcyclists, but a similar conclusion might
be had too of bicyclists?

sincerely,
Kate- who after a number of near misses, has now so many flashing lights
and pieces of reflective tape attached to her commuter bike, Prozac,
that the dear thing is likely mistaken for a very slow moving ambulance.
----------------------
BMJ 2004;328:857 (10 April), doi:10.1136/bmj.37984.574757.EE (published
23 January 2004)
http://bmj.bmjjournals.com/cgi/content/full/bmj;328/7444/857

Motorcycle rider conspicuity and crash related injury: case-control
study

Susan Wells, senior lecturer in epidemiology1, Bernadette Mullin, public
health physician1, Robyn Norton, professor of public health3, John
Langley, director of injury prevention research unit4, Jennie Connor,
senior lecturer in epidemiology1, Roy Lay-Yee, assistant research
fellow2, Rod Jackson, professor of epidemiology1

1 Section of Epidemiology and Biostatistics, School of Population
Health, Private Bag 92019, University of Auckland, Grafton Road,
Auckland 1, New Zealand, 2 Centre for Health Services Research and
Policy, School of Population Health, University of Auckland, 3 Institute
for International Health, University of Sydney, Sydney, NSW, Australia,
4 University of Otago, Otago, New Zealand

Correspondence to: S Wells s.wells{at}auckland.ac.nz


Abstract

Objective To investigate whether the risk of motorcycle crash related
injuries is associated with the conspicuity of the driver or vehicle.

Design Population based case-control study.

Setting Auckland region of New Zealand from February 1993 to February
1996.

Participants 463 motorcycle drivers (cases) involved in crashes leading
to hospital treatment or death; 1233 motorcycle drivers (controls)
recruited from randomly selected roadside survey sites.

Main outcome measures Estimates of relative risk of motorcycle crash
related injury and population attributable risk associated with
conspicuity measures, including the use of reflective or fluorescent
clothing, headlight operation, and colour of helmet, clothing, and
motorcycle.

Results Crash related injuries occurred mainly in urban zones with 50
km/h speed limit (66%), during the day (63%), and in fine weather (72%).
After adjustment for potential confounders, drivers wearing any
reflective or fluorescent clothing had a 37% lower risk (multivariate
odds ratio 0.63, 95% confidence interval 0.42 to 0.94) than other
drivers. Compared with wearing a black helmet, use of a white helmet was
associated with a 24% lower risk (multivariate odds ratio 0.76, 0.57 to
0.99). Self reported light coloured helmet versus dark coloured helmet
was associated with a 19% lower risk. Three quarters of motorcycle
riders had their headlight turned on during the day, and this was
associated with a 27% lower risk (multivariate odds ratio 0.73, 0.53 to
1.00). No association occurred between risk and the frontal colour of
drivers' clothing or motorcycle. If these odds ratios are unconfounded,
the population attributable risks are 33% for wearing no reflective or
fluorescent clothing, 18% for a non-white helmet, 11% for a dark
coloured helmet, and 7% for no daytime headlight operation.

Conclusions Low conspicuity may increase the risk of motorcycle crash
related injury. Increasing the use of reflective or fluorescent
clothing, white or light coloured helmets, and daytime headlights are
simple, cheap interventions that could considerably reduce motorcycle
crash related injury and death.



Introduction

Every day about 3000 people die and 30 000 people are seriously injured
on the world's roads.1 A disproportionate burden is borne by low to
middle income countries and vulnerable road users such as pedestrians,
cyclists, and riders of motorcycles and scooters.2 By 2020, road traffic
crashes are projected to be the third leading cause of death and
disability worldwide.3 Low motorcycle conspicuity, or the inability of
the motorcyclist to be seen by other road users, is thought to be an
important factor associated with risk of motorcycle crashes.4 This may
result from several factors, including size of motorcycle, irregular
outline, low luminance or contrast with the background environment, and
the ability to travel in unexpected places in the traffic stream.
Inexpensive measures can potentially enhance conspicuity—for example,
adding a light source and the use of light, bright, reflective, or
fluorescent colours.

Much of the epidemiological literature on motorcycle conspicuity
comprises historical cohort analyses investigating daytime use of
headlights and motorcycle crash rates before and after legislation or
ecological studies investigating regions with or without "lights on"
laws.5-12 We are aware of only four previous aetiological studies
investigating the association between motorcycle conspicuity and risk of
crash related injury.13-16 All were case-control studies conducted more
than 20 years ago, and none used a population based sampling frame.13-18
In three of these studies, daytime use of headlights was investigated
and found to be associated with reduced risk.13 15 16 Hurt et al found
that wearing a high visibility upper torso garment was associated with
lower involvement in crashes; however, control data were collected two
years after the crash data.13 No other case-control study has evaluated
the effects of colour of helmet or clothing. Despite the limited
evidence base, several countries—for example, Malaysia, the United
States, and Austria—have made daytime use of headlights mandatory, and
riders in other countries have voluntarily adopted this and other
strategies.

We investigated the association between a range of conspicuity measures
and the risk of motorcycle crash related injury in a country without
mandatory daytime headlight laws.



Methods

Study population and setting We conducted a population based
case-control study in Auckland, New Zealand, between February 1993 and
February 1996. The study methods and the sociodemographic, behavioural,
and vehicle related factors have been described elsewhere.19 20 At the
time of the study, the Auckland region had a population of approximately
950 000, of whom more than 90% lived in urban districts (1991 census).
The source population was all motorcycle drivers riding on motorways and
principal or arterial roads between 6 am and midnight in the Auckland
region. We excluded motorcycle drivers riding on residential roads and
riding between midnight and 6 am, as less than 2% of riding occurs in
these situations.21 We defined a motorcycle by using the ICD-9.CM
(international classification of diseases, 9th revision, clinical
modification) definition of a two wheeled vehicle.22 We applied the
definitions of geographical boundaries, time period, eligible vehicles,
and eligible roads in an identical manner to cases and controls. We
obtained informed consent from all participants.

Case selection We included in the study all motorcycle drivers or
pillion passengers who were killed, admitted to hospital, or treated in
a public hospital emergency department in the Auckland region, and who
had an injury severity score of > 5 within 24 hours of a motorcycle
crash. We conducted case finding prospectively through daily
surveillance of the region's four trauma hospitals and single coroner's
office. All injured people needing admission to hospital in the Auckland
region are admitted to one of these hospitals. We conducted interviews
face to face in hospital or by telephone if the participant had already
been sent home. For people who died as a result of the crash, we asked
next of kin to nominate a proxy respondent who could be interviewed.

Control selection We obtained a random sample of motorcycle riding by
identifying motorcycle drivers from 150 roadside survey sites in the
study region and time period. We randomly selected these sites from a
list of all non-residential roads in the region, in proportion to their
total length. We also randomly assigned time of day, day of week, and
direction of travel for each survey site. We photographed motorcyclists
as they approached the survey site, stopped them, and invited them to
participate in the study. We obtained a name, a telephone number, and a
suitable time for a follow up telephone interview. Where survey sites or
conditions were too dangerous for motorcyclists to be stopped (for
example, motorways, bad weather), we photographed the vehicles and
followed them up through their registration plate details. We
administered identical questionnaires to both cases and controls,
covering circumstances of the crash or current trip and
sociodemographic, personal, motorcycle related, and environmental
characteristics.

Conspicuity measures We asked participants if their headlight had been
off or on and, if on, whether it had been set to high or low beam. We
divided the self identified main colour of clothing worn into two
categories: frontal colour from waist up and frontal colour from waist
down. We defined motorcycle colour as the main colour of the motorcycle
from the front. As well as describing the main colour of their clothing,
motorcycle, and helmet, participants nominated the colour as either
light or dark. We asked participants if they were wearing any reflective
or fluorescent clothing or other articles such as a jacket, vest, apron,
sash, ankle or wrist band, or back pack including stripes, decals, or
strips.

Potential confounding variables We considered the following potential
confounders suggested by the literature and used in previous analyses of
this study19 20: age, sex, ethnicity, income, education, motorcycle
licence and insurance status, self reported alcohol consumption in the
previous 12 hours, years on-road riding experience, kilometres travelled
on the specific motorcycle at interview, posted speed limit, ambient
illumination, and weather conditions. All data were self reported except
for road type and traffic speed zones, which were ascertained by
environmental surveys. New Zealand has three main speed limit zones: 50
km/h in most urban areas, 70-80 km/h in restricted speed zones
principally on main highways, and 100 km/h on motorways and the open
road.

Statistical analysis We used SAS statistical software to conduct all
analyses, and we calculated odds ratios together with 95% confidence
intervals by using unconditional logistic regression. As this was a
population based study and the outcome of interest is rare, the odds
ratios calculated will approximate to relative risks. We fitted a model
to examine the independent association of each conspicuity measure and a
crash related injury. We assessed each potential confounder in turn and
included the variable in the final model if its inclusion changed the
odds ratio by 10% or more.23 We calculated population attributable risk
estimates according to methods developed by Greenland and described by
Rockwell.24 The formula uses relative risk estimates and the proportion
of cases exposed. We considered pillion passengers to be part of the
driver-motorcycle unit and did not include them in the analyses. We
stratified the analysis of use of reflective or fluorescent clothing by
ambient light conditions (daylight, twilight, night) but did not include
an interaction term for this in the logistic regression or multivariate
analysis as numbers were small.



Results

The cases were 490 motorcycle drivers (including 32 deaths), and
interviews were completed for 463 (95%). Thirteen drivers refused to
participate, and 14 could not be contacted. Of the interviews with case
drivers, we conducted 293 (63%) by telephone, 164 (35%) face to face,
and 6 (1%) by self completed questionnaire.

The controls were 1518 motorcycle drivers: 931 (61%) were identified at
sites where motorcyclists were stopped and 587 (39%) from photograph
only sites. Interviews were completed with 1233 (81%) drivers, of which
1189 (96%) were conducted by telephone. Most of the drivers not
interviewed could not be contacted; only 42 (3%) drivers refused to
participate.

Table 1 shows the sociodemographic characteristics of the study
participants and the distribution of potential confounding variables.
Men accounted for 94% of the motorcycle riding population in Auckland
during the study period; most crashes occurred in urban 50 km/h speed
limit zones (66%), during the day (64%), and in fine weather (72%).

View this table: [in this window] [in a new window]

Table 1 Sociodemographic, personal, and environmental characteristics of
motorcycle crash related injury cases and population controls. Values
are numbers (percentages)



Young motorcyclists, especially those under 20 years, are at increased
risk of injury compared with older riders.13 14 16 25 Table 2 shows age
adjusted and multivariate odds ratios of crash related injury risk
associated with conspicuity measures.

View this table: [in this window] [in a new window]

Table 2 Adjusted odds ratios of risk of crash related injury associated
with potential conspicuity enhancing measures. Values are numbers
(percentages) unless stated otherwise



Use of reflective or fluorescent clothing Nearly 20% of control drivers
were wearing some type of reflective or fluorescent clothing. Drivers
wearing reflective or fluorescent clothing had a 37% lower risk of crash
related injury than those who were not wearing such materials
(multivariate odds ratio 0.63, 95% confidence interval 0.42 to 0.94).
When stratified by ambient illumination (table 3), the protective
association seemed to increase with falling light levels, although
numbers were small at twilight, reducing the precision of the effect
estimate.

View this table: [in this window] [in a new window]

Table 3 Use of high visibility clothing stratified by ambient
illumination. Values are numbers (percentages) unless stated otherwise



Helmet colour The main colours of helmet reported by control drivers
were black (39.8%), white (30.6%), and red (13.8%). Compared with
wearing a black helmet, use of a white helmet was associated with a 24%
lower risk (multivariate odds ratio 0.76, 0.57 to 0.99). We found
similar associations for red and a combined group of yellow and orange
helmets, although these did not achieve standard levels of statistical
significance. Self nominated description of "light coloured" helmet
compared with "dark coloured" helmet was associated with a 19% lower
risk.

Headlight operation Of the 175 control drivers randomly surveyed at
night, 100% were using their headlight. At twilight, 91 (88%) of the 104
control drivers reported having their headlight turned on. Of the 954
control drivers randomly surveyed during the day, 719 (75%) had their
headlight turned on—609 (64%) on low beam setting and 92 (10%) on high
beam, with 18 (2%) unsure whether high or low beam was used. Overall,
voluntary use of headlight in daytime was associated with a 27% lower
risk of crash related injury (multivariate odds ratio 0.73, 0.53 to
1.00).

Frontal colour of clothing and motorcycle Approximately 80% of 1233
control drivers wore either black, blue, or brown clothing on the upper
body (955) and black or blue clothing on the lower body (988). Of the
main frontal motorcycle colours, 299 (24%) motorcycles were black, 282
were (23%) red, 188 (15%) were white, 183 (15%) were chrome or silver,
and 148 (12%) were blue. We observed no association between risk of
crash related injury and the frontal colour of drivers' clothing or
motorcycle. Similarly, no difference in risk occurred for self nominated
light versus dark coloured clothing or motorcycle.

Population attributable risk The population attributable risk is the
estimated proportion by which the incidence of crash related injuries
could potentially be averted if a specific risk factor was eliminated
from the population. In this population, assuming that the associations
described are causal and unconfounded, the population attributable risk
associated with not wearing fluorescent or reflective clothing was
approximately 33%. Other population attributable risks were 18% for
wearing a non-white helmet, 11% for wearing a dark coloured helmet, and
7% for not using headlights during the day.



Discussion

In this large population based case-control study we observed that
fluorescent or reflective clothing, wearing a white or light coloured
helmet, and voluntary daytime use of headlight were associated with
reduced risks of motorcycle crashes resulting in severe injury or death.
The protective association for high visibility clothing strengthened
with falling light conditions, providing additional support for the
validity of the findings. No significant differences in risk occurred
with the frontal colour of drivers' clothing or motorcycle.

Strengths and weaknesses of the study We were able to identify all
motorcyclists involved in a crash resulting in moderate to severe injury
or death from a large geographically defined base population. The
controls were a random sample of motorcyclists from the same study
population over the same study period. In this study the prevalence of
each characteristic in controls is an estimate of its prevalence in all
motorcyclists in the study region.

Most variables investigated were self reported, and recall bias may be a
problem. However, exposures such as colour of helmet, colour of
clothing, use of high visibility clothing, and operation of headlight
are less likely to be influenced by recall bias than other behaviours
such as alcohol consumption or speeding. Furthermore, cases may be more
inclined than controls to over-report having used conspicuity enhancing
measures as they analyse and apportion fault in a multi-vehicle crash.
The net effect would be an underestimate of the effects.

The validity of our findings depends on the ability to control for
confounding. In this study a wide range of potential confounders were
measured and modelled in the multivariate analyses. Riders wearing high
visibility clothing and white helmets are likely to be more safety
conscious than other riders. However, we were able to adjust for
sociodemographic variables, the propensity for risk taking behaviour
(such as younger age, alcohol consumption, licence status, and
motorcycle riding experience) and environmental characteristics (such as
light conditions, weather, and speed limit zones).

Comparison with previous research Bright colours worn during the day,
daytime use of headlight, and reflective or fluorescent clothing are
thought to enhance conspicuity by increasing the brightness contrast
between the surface or object it is on and the background environment.
The finding that helmet colour was associated with injury crash risk
whereas frontal colour of clothing was not was unexpected. Hurt et al
contended that the principal coloured surfaces with any real potential
for contribution to conspicuity are the fairing shield and the rider's
upper torso garment.13 They considered that the surface presented by
even a full face helmet was no more than 20% of that of an upper torso
garment and therefore the contribution to conspicuity would be expected
to be low. A possible explanation for our findings is that 80% of the
controls wore black, blue, or brown top clothing and black or blue
clothing from the waist down. Owing to the small numbers wearing light
coloured clothing, our study may not have had the power to detect an
effect of brightly coloured clothing if it existed. Our study was also
limited by the one "catch-all" category for reflective and or
fluorescent clothing. These materials offer maximum conspicuity
advantage in differing ambient light conditions—fluorescence at twilight
and reflective material at night, and we were unable to determine the
individual contributions.

Implications for prevention of injuries This study took place in a
predominantly urban area and in a country where motorcycles make up a
small percentage of all registered motor vehicles. Factors contributing
to poor conspicuity, such as contrast from the background environment
and ambient illumination, may differ between settings. The population
attributable risks are not generalisable as they depend on the
background prevalence of the risk factors in specific populations.
However, there is no reason to believe that the relative risk estimates
for the conspicuity measures investigated would not be generalisable to
other settings.

This seems to be the first population based aetiological study
investigating motorcycle conspicuity and risk of crash related injury
and death. The study suggests that low physical conspicuity is a
contributing factor in a significant proportion of road traffic crashes
causing injury. The social costs of motorcycling deaths and disability
are high, not only through premature deaths and hospital admissions but
also through costs of rehabilitation, lost income, sickness benefits,
insurance, property, and legal expenses as well as personal costs of
grief and suffering. This study supports the introduction of both active
and passive injury prevention strategies through laws requiring daytime
use of headlights and measures encouraging greater visibility of
motorcycle riders on the roads.

What is already known on this topic

Low conspicuity, or the inability of the motorcycle and rider to be seen
by other road users, is thought to be associated with motorcycle crash
related injury and death

Previous studies suggest a benefit from daytime use of motorcycle
headlights, although the evidence is limited

What this study adds

Wearing reflective or fluorescent clothing and white or light coloured
helmets and using headlights in daytime could reduce serious injuries or
death from motorcycle crashes by up to one third

We thank the participating motorcyclists; Angela Hursthouse, Kevin
Sherlock, Mark McLauchlan, and other staff at the Injury Prevention
Research Centre; staff at participating hospitals; and staff at the Land
Transport Safety Authority. Special thanks to Shanthi Ameratunga and
Joanna Broad for their critical review of the draft papers.

Contributors: SW was mainly responsible for the statistical analysis,
interpreting the data, and writing the paper. RJ, RN, BM, and JL were
mainly responsible for the study design, and BM was responsible for data
collection. RJ, RN, BM, and JL contributed to writing the paper. RJ, JC,
and RL-Y contributed to the statistical analysis, interpreting the data,
and writing the paper. RJ is the guarantor.

Funding: Health Research Council of New Zealand (HRC) and the Accident
Rehabilitation and Compensation Insurance Corporation (ACC). BM was the
recipient of an HRC Training Fellowship. The Injury Prevention Research
Centre and the Injury Prevention Research Unit were both jointly funded
by the HRC and ACC at the time of the study.