Vehicle Conspicuity

- a matter of life and death

Published:  01 January, 2007

How visible are your vehicles?

In July 2006, US Fire Administrator Charlie Dickinson announced that a 115 firefighters died in the line of duty during 2005. Most of the casualties (55) were caused by heart attacks, six died of Cerebral Vascular Accidents and there were four multiple-firefighter fatality incidents.
Tragically, twenty five firefighters were killed on duty in vehicle crashes.
Year after year firefighters get killed in accidents on the road, especially in the US. In response to this, United States Fire Administration (USFA) initiated the Emergency Vehicle Safety Initiative, a project with a long-term goal of reducing the number of firefighters killed responding to and returning from emergencies and suffering accidents on the roadway.
USFA carried a follow on-study of Emergency Warning Lighting Systems with the Society of Automotive Engineers (SAE). This second phase of the project -the first study was started in 2003 ­investigates how to effectively overcome the disorientation of motorists caused by the day and night­time use of emergency warning lights, through design, technology, and operating practices.
The Under Secretary of the US Homeland Security for Emergency Preparedness and Response said: “I am pleased that the UFSA is continuing its work with the SAE to study the impacts of lighting colour and emergency vehicle visibility on the safety of firefighters responding to or returning from emergencies.” The first part of the research project involved an examination of crash data of fire apparatus, as well as incidents where firefighters have been struck and killed on the road while attending incidents where the use of emergency lighting may have been a factor. Summary findings from the SAE for the first phase of this study are published in the July 2005 report: “Inferences about Emergency Vehicle Warning Lighting Systems from Crash Data.” In this report some very interesting conclusions are drawn about the use and strength of emergency vehicle warning lights - useful data for the US and Canada and for other countries worldwide. Warning lights and conspicuity tape on emergency vehicles are designed to increase the visibility for other road users in daylight as well as darkness. The report states that lights and tape are probably very good at that. It points out:
“However, there has been concern that, if they are too strong warning lamps could also increase the risk of certain types of crashes. Thus far, empirical evidence on this issue from crash data has been limited. The purpose of this project is to examine several sources on information about emergency vehicle crashes and to use that infor­mation to make tentative recommendations about how warning lamps could be modified to increase safety.” The report states that the intensity of the warning light as an alerting device is determined by several variables, naming light intensity, flash rate, abruptness of flash onset and offset, colour, number of lights and the configuration of those lights. The influence of these variables on other road users may be either negative or positive, but the effects are complex.
“Stronger lamps may be more effective in getting drivers to notice emergency vehicles, thereby avoid many potential crashes. However, there may also be some negative effects of warning lights -including visual effects such as glare and masking; and cognitive effects such as distraction, confusion and disorientation.” The question is asked; if greater strength also increases negative effects of warning lights, then optimising the design of warning lights may involve determining the strength of lights that keeps the best balance between the negative effects and conspicuity? The researchers examined three sources; the crash databases for the states of Missouri and Florida; the US Fatality Analysis Reporting System (FARS) the institution that registers all fatal crashes in the US; and specialist database that that keeps all fatal firefighter traffic collisions. After scrutinising these databases on specific queries the researchers from SAE came with several conclusions in which the state databases gave the most directly applicable findings. “Emergency vehicles are involved in fewer angle crashes in the dark, consistent with the hypothesis that warning lights are effective in preventing those crashes because the lamps are more salient in darker ambient conditions.”
Furthermore, it adds that emergency lights on fire trucks built in 1998 and onwards are almost definitely safer than lights manufacturers before that time, as it suggested by a reduction in the number of crashes when responding to an emergency. Results from a research of police accident reports in Florida revealed that for crashes involving fire tenders suggested that there may be a large number of multi vehicle crashes (30%) in which the other road users (drivers) did not see them in time.
So what does this report recommend?
Stronger warning lights are suggested as a possible solution as there does not seem to be strong evidence that stronger lights would result in significant negative effects. The second recommendation is that since there is a trade-off between conspicuity of emergency lights and the negative effect of those same lights, new design possibilities that change that trade-off are an option for safer road use. Here’s what the reports says: “The results of this project lead to several possible approaches for further research to better understand how warning lamps affect emergency vehicle safety. “First, in order to overcome the limits of existing crash databases, it may be valuable to directly observe the behavior of other vehicles around an emergency vehicle engaged in emergency operation, either while in transit or while parked at an emergency site. “Second, the possibility that warning lamps at night reduce the visibility of emergency personnel as pedestrians should be directly studied with human-performance field work,” it concludes. For more information on research into vehicle conspicuity, please visit: www.usfa.dhs.gov/research/safety/vehicle.sthtm

  • Operation Florian

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