Research
Police lighting: what forty-two years of research actually found
Five studies between 1978 and 2020, by four separate teams, none of whom set out to agree with each other. They did anyway.
The light bar is the most visible part of a police car and the least tested. The engine, brakes, tyres and transmission go through the Michigan evaluations every autumn, measured to the hundredth of a second and published. The thing that defines the vehicle as a police car gets fitted without anyone measuring what it does.
Four times in half a century, somebody did. Every one of those studies was paid for out of public money, published, and then left in a government archive. Read in order they make an argument none of them makes alone.
The short version
| Year | Who | What they found |
|---|---|---|
| 1978 | National Bureau of Standards | No national standard. Sixteen states permitted blue, under six different rules. Part I is headed “The Present Chaos” |
| 1982 | Illinois State Police | Light bars cost 12% of fuel economy. 381 crash files showed no measurable safety benefit |
| 1984 | Illinois State Police | Sixty cars ran without roof lights for two years: a fifth the accident rate. Made standard issue |
| 2020 | Virginia Tech | Brighter lighting moves traffic over sooner — and hides the officer standing beside the car |
| 2020 | US Fire Administration / NIJ | Retroreflective material can be overdone. Battenberg works in Britain only because British drivers learned it |
The recurring finding, from four teams who never spoke to each other: more is not better, and past a certain point it works against the thing it is there to protect.
Read them in this order
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1 of 5
The 1982 study that found police light bars cost money and saved nobody
The Illinois State Police measured what their light bars burned in fuel, reviewed 381 of their own crash files, and took the bars off sixty cars to find out. Two years later they changed the whole fleet.
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2 of 5
The police lights that make the officer harder to see
A Virginia Tech study measured how police lighting changes driver behaviour. Brighter lights moved traffic over sooner — and degraded drivers’ ability to see the officer standing beside the car.
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3 of 5
Why American police cars look the way they do
Somebody counted every colour, logo and stripe across fifty city and forty-nine state forces. The black-and-white is not even the most common American police car.
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4 of 5
Invisible and unmissable at the same time
For twelve years an American officer was struck and killed by a vehicle about once a month. The fix for a patrol car turns out to be the opposite of the fix for a fire engine.
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5 of 5
Part I: The Present Chaos
In 1978 the National Bureau of Standards surveyed emergency vehicle lighting across fifty states and headed its first section “The Present Chaos”. Almost nothing it recommended has happened.
Why 1978 is last
Chronologically it comes first. But it is the hardest of the five to care about until you know what the lights actually do — so it reads best once the other four have shown you. Start anywhere if you prefer; each stands alone.