Roadside Safety: Retro-Reflective Cars and Auto-Dimmed Lightbars

In February 2011, Lt. Andrew Klane of the Collision Analysis and Reconstruction Section (CARS), and an officer participated in a “lightbar” test at the Massachusetts State Police EVOC facility in Devens, Mass. The purpose of this test was to make observations of a Whelen lightbar, which had been modified with a low power switch and different flash patterns.

Slower Flash Rate

The low power switch allowed for the reduction in intensity of the emergency lights and the different flash patterns allowed the use of a slower flash rate and a less complex flash pattern. The cruiser that the lightbar was affixed to had also been outfitted with retro-reflective graphics.

The results of this test are promising. During darkness, the low power switch was activated and the flash pattern was slowed down. The result of these two changes was the outside profile of the MSP cruiser became more visible. In addition, the emergency lighting from the cruiser produced less glare. These attributes proved helpful in determining the position of the cruiser when parked. In addition, the changes made the officer operating that cruiser more visible as he was positioned next to and in front of the cruiser.

Reflective Tape

Next, a sample of reflective vehicle tape (Reflexite) was added to the testing. When applied to the test cruiser, this tape offered increased benefits to the nighttime conspicuity by marking the edge of the cruiser. As a result of the testing conducted at the EVOC facility, conducting further research into the concept of retro-reflective vehicle markings was planned.

Extensive research was conducted on vehicle conspicuity and retro-reflective graphic treatments on emergency vehicles. The purpose of these treatments is to increase the vehicle contrast and allow the vehicle to stand out against its background. Vehicle contrast and conspicuity becomes even more important when motorists are presented with a visually challenging background where numerous objects are competing for visual attention.

Daytime Visibility

Daylight conspicuity markings seen on vehicles are of high fluorescent colors found in certain visual ranges such as yellow, green, orange and red. These colors are capable of attracting motorist’s attention in the central and peripheral field of vision over greater distances than conventional colors. These colors may also have retro-reflective properties applied to them but they do not necessarily have to.

Retro-reflective applications, on the other hand, may be found applied to many different graphics, have no self illumination properties, and remain passive until a light is shined upon them. Thereupon the treated surface then reflects light back towards its source. The State Police decals and door seal on our marked cruisers are an example of this. They are relatively “flat” until a light is shined upon. The amount of light that is reflected back to the source is a direct result of the amount of light shined upon the surface. The properties of retro-reflectivity are also affected by the angle of the incoming light and the angle of the viewer to the source of the light and the reflective material.

An example of both concepts used together can be found in the short rain jacket issued to all of our officers. The jacket is fluorescent lime green and has retro-reflective stripes affixed to it. In the daytime the fluorescent color of the jacket is easily seen, however, the stripes appear flat and contribute little to its overall visibility. At night the stripes shine brilliant light back towards the source of the light. However, the fluorescent color of the jacket has little effect on its ability to be seen at night at any significant distance.

Visual Feedback

Driving is a task that requires visual feedback. In all lighting conditions visual feedback from an emergency vehicle is critically important for approaching motorists to determine the vehicle size, shape, location, direction of travel, closing distance, and time available for crash avoidance. Motorists are often distracted, fatigued or impaired.

Additionally, as individuals get older, their eyesight naturally deteriorates and makes the process of seeing contrast, particularly at night, more difficult. Along with this, many older drivers see halos, blurring, and are severely affected by glare.

During daylight hours, approaching motorists have the benefit of being able to see the vehicle that the emergency lighting is “attached” to. Additionally, they can see geographical landmarks that help determine the vehicle’s location within the roadway which is critical in collision avoidance. Generally, there is sufficient visual feedback to accomplish safe navigation beyond parked or slowly moving emergency vehicles.

In darkness however, visual feedback is greatly reduced. The area within the roadway which the emergency vehicle is occupying is not easily visible due to the obvious fact that it is dark and any ambient light that may help identify the vehicle location may be overcome by the glare of the emergency vehicle lighting or other vehicle headlight glare present in the area. This can not be overlooked as our cruisers often occupy the entire breakdown lane. There is little room for error on part of the approaching and passing motorists.

The concept of applying retro-reflective graphics to a vehicle can assist the motorist with visual clues that can increase their ability to safely navigate beyond the vehicle. From these visible cues, the motorist is better able to make decisions about avoiding the object if required to do so. The advantage of additional visual clues becomes crucial for approaching vehicles operating at highway speeds simply because the distance covered over time is so great.

Within the United States, a 2009 change to the Standard for Automobile Fire Apparatus requires retro-reflective striping in multiple locations. Research performed by NHTSA suggests retro-reflective conspicuity treatments applied to U.S. heavy truck trailers since 1992, with a retrofit requirement in 1999 have been effective at reducing crashes at night.

These findings echo several other studies on retro-reflective application treatments to vehicles in European countries. A 1999 United Kingdom study found that fully outlining (large) vehicles with contour markings increased drivers’ ability to detect them both day and night, as well as judge their size and distance.

In an effort to make our cruisers more visible during the hours of darkness, it is recommended that a cruiser retro reflective package be installed. This would consist of, at a minimum, retro reflective tape along the rear and front bumper corners. This particular application illuminates the exterior corner profile of the vehicle which provides the approaching motorists with critical visual clues helpful for crash avoidance.

Another recommendation is to change the State Police decals and door seal to a more reflective material made from “prismatic” reflective tape instead of “glass bead” reflective tape. Prismatic tape is more reflective than glass beaded tape, maintains more reflective properties when wet, and is able to maintain higher reflective properties at greater angles.

In addition to recommending a retro-reflective package, it is strongly recommended to move forward with some application of a switch or sensor which would decrease the intensity of the cruiser emergency roof lights during periods of darkness. The latest Edition of the Manual on Uniform Traffic Control Devices requires that arrow boards used in work zones be capable of being dimmed by at least 50 percent and that they shall be dimmed for nighttime operations. Furthermore, it suggests that arrow-boards be used at full intensity for daytime operations.

There are numerous strategies that must be considered when trying to prevent a crash from occurring. There may be a combination of factors which include operator impairment, environmental limitations, and poor decisions made on behalf of the officer. Motorists can not be expected to avoid a crash with cruisers or officers that they can not see or are not given enough time and distance to avoid.

Lowering the intensity of the cruiser lighting and adding retro reflective markings is expected to decrease the amount of crashes experienced in darkness by officers assigned to patrol functions with the Division of Field Services. These changes will likely have little effect on the amount of crashes occurring during daylight hours.

The need for continued testing and research in this area is clear. Additionally, a detailed crash database is needed to determine exactly the type of crashes being experienced by officers assigned to the Division of Field Services who are operating or standing in proximity to marked cruisers.

The vehicles in the pictures in this article show different applications and colors of “Reflexite” prismatic tape applied to a 2010 Ford Explorer and a 2009 Crown Victoria. In one of the photos, the Ford Explorer is parked next to an identical cruiser with no reflective tape. The picture was taken from a distance of about 150 feet with the two cruisers illuminated by the low beams of a Ford F-150 pickup. The product applied to the cruiser is one half inch wide white prismatic Reflexite tape. The “State Police” decal is standard “glass bead” tape.

Another picture shows a 2009 Crown Victoria with standard glass bead reflective “State Police” decal. Also shown is a 2010 Explorer, which has been modified with the highest level of prismatic “State Police” decal and prismatic “Collision Analysis” decal. Additionally, another image shows blue prismatic tape has been applied to the bumper corners in lieu of the white prismatic tape. Also pictured is a 2009 Crown Victoria where the standard glass bead decal was replaced with a high level of prismatic “State Police” decal. Again, the illumination is from dim lights about 150 feet away.

Another picture shows the two previous cruisers with full rear facing emergency lighting activated. Note the reflection of the “prismatic tape” on the inside of the driver side door on the left cruiser. This is the issued tape when the cruiser was delivered new from fleet.

Sergeant Stephen Marsh is with the Collision Analysis and Reconstruction Section of the Massachusetts State Police.  

Published in Police Fleet Manager, Nov/Dec 2011

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