Driving Through the Deluge: How Rain Affects Traffic Speeds Across Major Cities

When the clouds open up, traffic patterns shift almost instantly. But just how much does a rainy day impact your commute? Using Geotab data, we’ve analyzed the average speed change during rain events across major metropolitan areas to see which cities keep moving and which ones grind to a halt.

The Rain-Speed Rankings

The data reveals a significant disparity in how different urban environments and driving populations respond to wet weather. While most cities experience a noticeable slowdown, the severity ranges from a minor inconvenience to a major logistical hurdle.

Key Takeaways from the Data

• The Big Apple Takes the Biggest Hit: New York City saw the most dramatic impact, with average speeds dropping by 4.1% during rain events. Given NYC's already high density and complex infrastructure, even a small percentage drop can lead to massive gridlock during business hours.
• The Expected vs. The Unexpected: Interestingly, Seattle—a city famous for its drizzle—experiences a notable 2.5% slowdown. This suggests that even "rain-ready" cities aren't immune to the physics of wet pavement and reduced visibility.
• The Outliers: While most cities saw a decrease, Miami remained remarkably consistent at 0.0% change. Even more surprising, Chicago actually saw a slight increase in average speed of 0.4% during rain. This could be attributed to a higher volume of drivers opting for highways over local roads or changes in pedestrian activity that clear up intersections.

What This Means for Fleet Managers

Understanding these regional responses to weather is critical for accurate route planning and ETAs. In a city like New York or Denver, "rain-aware" dispatching can help account for that 3-4% loss in efficiency before it impacts customer satisfaction.