Research
The police car has to be invisible and unmissable at the same time
Over twelve years, an American police officer was struck and killed by a vehicle roughly once a month. A federal study went looking for the fix — and found that the answer for a patrol car is the opposite of the answer for a fire engine.
Three articles on this site already deal with police lighting: the 1978 survey that called the whole field chaotic, the Illinois trial that took the bars off sixty cars, and the 2020 work showing brighter lights hide the officer. All three are about lamps.
This one is about paint, tape and a contradiction nobody else has to solve.
The reason it matters
The study opens with the figures that justify it, and they are worse than most people assume.
In 2008, as in each of the ten years before it, more American law enforcement officers died in traffic-related incidents than from any other cause. Over the preceding twelve years, an average of one officer per month was struck and killed by a vehicle.
It is not confined to policing. Of 114 firefighters killed on duty in 2008, 29 died in motor vehicle crashes. At least 67 EMS providers were killed in ground transport events across the six years from 1992 to 1997.
The most dangerous thing about being a police officer, measured by what actually kills them, is traffic.
The contradiction
Here is the problem that makes a patrol car different from every other emergency vehicle, and the study states it plainly.
A fire engine wants to be seen. Always, by everybody, from as far away as possible. So does an ambulance, and so does a school bus — which is why school buses are that particular yellow and nobody argues about it.
A police car does not. Officers conducting certain enforcement and patrol activities may want to be almost invisible to other drivers. A patrol car that can be identified at half a mile cannot do traffic enforcement, and a police vehicle is expected to do both jobs in the same shift with the same paint.
And there is a second, darker version of the same tension. The report notes a point of view that emergency vehicles parked off the roadway at an incident should reduce their conspicuity — to avoid being hit by drivers who are potentially attracted to activated warning devices.
That phenomenon has a name in the trade and no settled evidence behind it. The study’s own key findings list it carefully: there is limited scientific evidence that drivers are “drawn into” highly visible emergency vehicles. Limited is not none, and it is not proof either. It sits in the report as an unresolved worry, which is the honest place for it.
What the study concluded
| Key findings |
|---|
| Increased use of retroreflective materials holds great promise for enhancing conspicuity |
| Both visibility and recognition matter — being seen is not the same as being understood |
| Contrasting colours help drivers locate a hazard amid roadway visual clutter |
| Fluorescent colours, especially yellow-green and orange, offer higher daylight visibility |
| Limited evidence that drivers are “drawn into” highly visible emergency vehicles |
| It is theoretically possible to over-do retroreflective material and interfere with drivers’ ability to recognise other hazards |
| Battenburg’s effectiveness in the UK appears primarily related to its association with police vehicles in that country |
That last line is the one worth pausing on, because it arrives here from an entirely separate research team and matches what Virginia Tech found a decade later. Battenburg does not work because of the geometry of the checks. It works because British drivers have been taught what it means.
Two independent studies reaching the same conclusion is worth more than either of them alone: conspicuity of that kind is learned, and cannot be imported.
The elegant answer
The study’s list of opportunities contains one line that resolves the whole contradiction, and it is a genuinely clever piece of engineering thinking.
For law enforcement vehicles, it says, retroreflective material can be concentrated on the rear — maintaining stealth from the front and the side while protecting the vehicle where it is most likely to be struck.
A patrol car parked on a shoulder at night is in danger from behind. An officer running stationary traffic enforcement needs not to be recognised from in front. Those are different surfaces of the same car, and you can treat them differently.
The car can be invisible where it needs to be invisible and unmissable where it needs to be unmissable, because those are not the same side.
The other recommendations follow the same physics-first logic:
Outline the vehicle’s boundaries with contour markings, so a driver perceives size, position and direction rather than just a light.
Concentrate the material low on the vehicle, because retroreflective sheeting does not glow — it returns light to its source, and the source is an approaching car’s headlamps, which sit low.
Use high-efficiency material to get the same conspicuity from less surface area — which, on a police car, means less of the vehicle committed to being visible.
Why retroreflective tape is not paint
The technical section explains something most people get wrong, and it changes how you read every marked car.
Retroreflectivity requires an external light source. The material does nothing on its own. It works by returning light almost exactly back along the path it arrived on — which means a stripe is brilliant to the driver whose headlamps are lighting it and nearly invisible to a pedestrian standing beside them.
Two technologies do this. Glass spheres bonded to a substrate, and engineered microprisms — tiny cube corners. Microprismatic sheeting is the more efficient of the two. But beads hold their performance across a wider range of viewing geometries, which matters enormously on a vehicle that drivers approach from every conceivable angle rather than head-on like a road sign.
And a warning for anyone specifying it: the ASTM standard lists ten types of retroreflective sheeting, and a higher type number does not mean a better material. The numbers identify different performance specifications, not a ranking.
Who was in the room
It is worth recording who produced this, because the composition explains the report’s even-handedness.
The expert panel included the International Association of Chiefs of Police, the International Association of Fire Chiefs, the National Fire Protection Association, the National Institute of Justice, the National Institute for Occupational Safety and Health, three representatives of the National Highway Traffic Safety Administration, the National Volunteer Fire Council, the General Services Administration and the University of Michigan Transportation Research Institute.
The site visits went to 3M, Avery-Dennison and Reflexite — the people who make the material — and to the Arizona Department of Public Safety, Boston EMS, Rosenbauer America and UMTRI.
A study that visits the manufacturers and still writes down that you can overdo their product is one worth reading.
What it means for the cars
Every article on this site about police lighting has arrived at the same shape of answer from a different direction. 1978: no agreed meaning. 1982: the hardware was not earning its place. 2020: brighter can hide the officer. And here: more is not automatically better, the pattern only works if the public has learned it, and the right amount of visibility depends on which end of the car you are looking at.
The police car is the only vehicle on the road required to be conspicuous and inconspicuous in the same shift. Nothing in fifty years of research has resolved that, because it is not a research problem. It is the job.