How To Calculate Your Exact Commute Times In Rain And Snow

License plate-reading cameras in London allowed civil engineers to make some amazing calculations for commuters.
Copyright Stephen Craven, licensed for reuse under CC BY-SA 2.0

Seeing some snow outside? Better budget in 7.6 percent more travel time for your morning commute.

In a new study, a team of civil engineers calculated incredibly precise numbers for how weather affects car commute times in the Greater London area. Here’s the scoop:

Precipitation Travel Time Increase
Light rain 0.1-2.1%
Moderate rain 1.5-3.8%
Heavy rain 4.0-6.0%
Light snow 5.5-7.6%
Heavy snow 7.4-11.4%

The engineers also studied temperatures, but found they do not affect commute times. Thanks, engineers.

The study used some modern tech to count cars. The researchers, a team of three from University College London, grabbed data from government-owned, license plate-reading cameras installed all over the city. That let them track individual cars as they began and ended trips.

These findings could be useful to urban planners, the researchers wrote in a paper they published in the Journal of Transport Geography. In fact, for years, other engineers have performed similar studies in other cities. Those studies focused on less dense, and thus easier to count, cities than London. It turns out that the degree to which people slow down in rain and snow depends on the city, though most studies, like this London one, found that heavier precipitation means slower commutes.