Bright streetlights may cause more accidents, despite urban planner wisdom claiming otherwise

Brighter LED street lights don’t prevent accidents – in fact they may do more harm than good, according to a prominent statistician, who says the accepted science on street lighting is wrong.

Studying nearly a decade of accident data for 132 areas of Birmingham, UK, Dr Paul Marchant and team found that the road accident rate actually rose where bright broad-spectrum lighting such as LEDs had been installed – and no evidence was found for the brighter lamps leading to any improvement in road safety, day or night.

Marchant says some reasons for this could be changes in driver behaviour as new lamps are installed. “Perhaps in areas with more light changes, the roads seem to become more major, attracting more traffic and/or higher speeds at all times,” he told Transit Jam. “Perhaps there were new developments in the city, attracting both more lights and more traffic.”

But certainly Marchant’s findings are a world apart from other claims of “tens of percent improvements [in road safety] due to new lighting” that are used to promote new street lighting projects worldwide.

Bad science

Institute of Public Works Engineering Australasia (IPWEA) guidance note on sustainable street lighting draws on flawed research into the safety benefits of brighter street lighting, according to Paul Marchant

In fact, Marchant says a landmark 2013 paper used by urban planners to justify expensive new lighting in countries from the UK to New Zealand is simply “bad science”, creating a narrative of a safer world under bright white LED lighting through a flawed analysis.

That paper, by consultants Michael Jackett and William Frith, looked at a snapshot of lighting at 152 road sections across nine New Zealand urban territories. The consultants found “a statistically significant dose–response relationship … between average road luminance and safety across all traffic volume groups, with an indication that the relationship may be stronger where more serious crashes are involved.”

The finding is pure illusion, according to Marchant, who accuses the paper of “Cargo Cult Science”, to use Richard Feynman’s phrase, and suffering a number of fatal flaws including poor study design, poor statistical practice, statistical errors, cosmetic analyses, poor publishing practices and a lack of openness and transparency in publishing data.

The consultants, Marchant says, did not account for road conditions – wet or dry, for example, or traffic volume, both key variables in building an accident model – and Marchant says data that didn’t fit the hypothesis was discarded. “Jackett and Frith have not only not published their data but have not responded to requests to gain access to it,” Marchant wrote in a March 2020 commentary on the work.

But he says the paper is often used to justify expensive new street lighting projects around the world, despite better quality research offering different conclusions. For example, the Australian Government’s “Smart Lighting Smart Controls (SLSC) Roadmap to smart lighting” cited the paper complete with a graph showing an almost perfect correlation between luminance and safety. “Clearly nobody from the many organisations and technical advisors engaged in SLSC spotted the fact that the R² = 0.99 [a measure of correlation fit, with 1 being perfect], impressive as it is, is a gross misrepresentation of the empirical evidence,” writes Marchant.

One of the original authors of the paper Marchant dismisses, Michael Jackett, has defended the research. “The statistics were fairly mainstream and used two different methods, with both giving similar resultys. The results were not dissimilar from a much larger USA study published shortly afterwards.”

Jackett says his paper was extensively peer reviewed at the time “by the very reputable Journal in which it was published, and no comments like we now hear from Paul [Marchant] emerged. We would request people to read it for themselves.”

Jackett also says it is not a “trivial, low cost option” to retrieve the data from the 6-year-old study, as Marchant has requested.

Earth Hour: only half the story

301 E 209th Street, New York, 1934 – part of a study into street light impact on tree seasons. Today, according to Google Street View, the house remains… the trees didn’t make it (photo American Journal of Botany)

Even without road safety benefits, LED lights are the darlings of the environmental movement. With Earth Hour rolling around again tonight, and lighting under the spotlight for 60 minutes, activists will be highlighting the need for such low carbon solutions in our cities. LED lighting is more energy efficient and requires less maintenance than traditional street lighting: replacing all US filament street lighting with LEDs could deliver an energy saving equivalent to powering 5.8 million homes, for example.

But they also come at an environmental cost often not factored into the “low carbon” economy. The whiter lights play havoc with natural systems, echoing concerns of almost a century ago as New York first installed fixed filament street lighting: a 1934 study found New York City trees near street lights dropped their leaves later in the year, confused by the artificial light.

Some find it also interrupts sleep patterns – the so-called “blue light” effect now seen in everything from streetlights to mobile phones.

New billboards dazzle drivers and yet are often touted as “low carbon” solutions

But because they use less energy, the movement against excessive public lighting has waned like a darkening moon. Non-essential lighting such as LED billboards are now an accepted, even celebrated, part of our city culture. For example, commuters in Central, Hong Kong, will have noticed a new billboard unveiled last week on either side of the Entertainment Building: a dazzling 60-foot-high screen that even shades the sunlight. One green group, Green Sense, objected to the launch of SOGO’s Causeway Bay screen, the largest in Asia, in 2017, but years later the billboard continues to pump out the pixels to promote mobile phones, cars and beauty products.

Marchant says, in his personal capacity, he believes such billboards could also contribute to accidents “as they are designed to be distracting”.

“There is a glare issue too which, I understand, disproportionately affects older people,” says Marchant.

Astronomers (which Marchant also counts himself as, declaring it as a “conflict of interest” in his work) also detest the new brighter lights and the light pollution they bring; white streetlights can contribute up to four times as much nighttime sky glow as amber-hued sodium lamps of the same luminous output.

And although Michael Jackett and Paul Marchant don’t see eye-to-eye on statistics, they both share a passion for protecting this darkness. “I applaud Paul being involved with protecting the darkness of the night sky – I am also active in this area,” says Jackett. “Maintaining control on sky glow is going to require careful and intelligent use of the many LED technologies now available,” he says.