State DOTs and highway agencies use a range of fleet vehicles to accomplish operational, maintenance, and construction activities. Safety protocols have been established at each of these organizations to ensure highway workers conduct their activities under the safest conditions possible. One commonly used safety measure is the installation of warning lights on highway agency vehicles. Warning lights are available in many colours and patterns and notify the travelling public that they are approaching highway work-related activities. Drivers should be able to see the lights at a sufficient distance to let them perceive and react to the upcoming activity. Because the use of red can be confused with emergency vehicles, KYTC prohibits the use of red on work vehicles. National standards on warning lights for highway agency vehicles do not exist. Therefore, state DOTs and highway agencies have discretion to use a wide array of colour arrangements, light sources, locations, and other related factors when establishing their respective warning light programs. Currently, the Kentucky Transportation Cabinet (KYTC) relies on a combination of regulations, guidelines, and internal policies to govern its vehicle warning light program. The primary source of authority stems from legislative requirements contained within the Kentucky Revised Statutes (KRS). In addition, KYTC has developed internal policies and guidelines that dictate how warning lights are installed and operated on its vehicles. Another guidance document, the Manual on Uniform Traffic Control Devices (MUTCD), frequently guides the oversight of traffic control devices, such as signs and signals, but it contains limited guidance pertaining to warning lights on work vehicles. The Kentucky Transportation Center (KTC) reviewed vehicle warning light practices found at other state DOTs across the U.S. As part of this effort, KTC researchers reviewed studies conducted by the American Association of State and Highway Transportation Officials (AASHTO), which publishes the best single-source document on warning lights. Various state DOTs and/or affiliated research agencies were studied as well. Most often, these studies examined the colours used in warning light installations. Sometimes they identified other factors of interest, such as the light source, form of light signaling (i.e., flashing or rotating), what times of day the lights were used, and where lights were positioned on vehicles. A majority of studies indicated that amber was the primary vehicle warning light colour used by state DOTs on highway agency vehicles, although other colours were sometimes used. Other warning light characteristics, such as duration and placement, varied across state DOTs. KTC researchers conducted two external surveys to identify existing practices, trends, and options for vehicle warning light systems. In the first survey, KTC conducted an online survey to identify the LED light colours commonly used in vehicle warning light systems. This online survey relied upon three approved LED vendors from KYTC’s approved vendor list. This survey revealed that LED lights are primarily available in the colours of amber, blue, green, red, and white. KTC followed up the online survey with phone calls to approved KYTC LED vendors and learned that the fluorescent yellow-green colour does not exist as a product option. In the second survey, KTC researchers gathered more information on state DOT warning lights practices and procedures. The research team then analysed survey results to identify usage trends and best practices. KTC distributed this survey to state DOTs and other highway agencies through the State Highway Safety Engineers LISTSERV database. The survey contained 16 questions asking about various facets of warning lights’ usage on highway agency vehicles and specifically, information related to lighting system colours, sources, intensity, and the placement of lights. The survey also collected data on the responding agency’s name, the type of organization, and its warning light policies and regulations. Furthermore, it asked respondents to identify any previous studies conducted on highway vehicle warning lights. KTC received 16 responses. All of the responding agencies reported using amber lights as part of their overall warning light ensemble, with LEDs as a primary light source. All agencies relied upon internal policies and regulations to guide their warning light program efforts. Many state DOTs also placed warning lights on the rooftops of highway vehicles to provide 360- degree visibility. Finally, state DOTs often tried different approaches to differentiate among vehicles: varying colours by highway vehicle type and requiring different light source intensities during daytime and nighttime conditions. KTC researchers recommend the use of amber and white colours for KYTC work vehicles, an asynchronous flashing pattern with slow flash frequencies, and LED bulbs. Other recommendations include placement of warning lights at high elevations on the vehicle and against a solid-colored background. Continued investigation is required for determining the feasibility of the colour yellow-green as a viable warning light colour. (Author/publisher)
Samenvatting