With climate change leading to more extreme and prolonged heavy rainfall across the northern hemisphere, flooding has become a growing concern, especially during autumn and winter. While the usual worries around flooding focus on travel disruption and damage to homes, the leading cause of death during such events is actually related to driving through floodwater. In recent years, several high-profile incidents in England, including Derbyshire (2021), Liverpool (2023), and Lancashire (2024), have highlighted the deadly risks of this behavior. Researchers have been investigating why people decide to drive through floodwater and how to better warn drivers of the dangers involved. Many drivers believe the worst outcome is just damage to their car, but the reality is far more severe. Driving through even shallow floodwater can be life-threatening, as cars can float and be carried downstream, leading to drowning. A national survey of 185 drivers found that while most understood that water depth is a key factor—80% correctly identified that depths above 25cm are unsafe—many failed to recognize the risks of fast-moving water. When asked how they would judge water speed, drivers mostly focused on depth, not flow rate. This misunderstanding is particularly concerning. While deep water can immobilize a car, fast-moving water can sweep it away. Modern vehicles tend to float initially due to their sealed construction, and if they hit an obstacle or overturn, the risk of drowning increases significantly. Drivers often rely on the experience of other cars to gauge whether it’s safe to proceed, but this is not reliable. Instead, they should look for signs like water gauges at fords or how high the water has risen on roadside objects like signposts or fences. Even cars of the same size can react differently in water, depending on where their air intakes are located—differences that can affect how they float or move in flood conditions. Currently, the UK’s highway code lacks specific guidance on how to handle floodwaters or drive through flooded roads. Static flood signs, which are often placed on roads, are not very effective, as drivers are more likely to obey speed limits or stop signs than to turn around for a static sign. Many drivers distrust these signs because they are sometimes left in place long after flooding has passed. To address this, researchers tested a dynamic LED signage system that provides real-time flood alerts. In tests, drivers found the dynamic signs more effective and memorable than static ones, especially for the prototype flood warning sign. The dynamic signs captured significantly more attention from drivers, suggesting they could improve safety by encouraging more timely responses to flood conditions. If you encounter floodwater on a road, only drive through it if the depth is less than 10cm for a standard car or no more than 30cm for an SUV. Remember that the deepest part may not be in the center of the road, and ripples on the water’s surface can indicate fast-moving water, which is more dangerous. If you are unsure, the safest option is to turn around and find an alternative route.