In February 2025, a major multi-vehicle collision occurred on the E18 highway outside Enköping, Sweden. What began as families heading off for their winter holiday (sportlov) quickly turned into a chaotic scene when black ice and high speeds created dangerous driving conditions. Multiple vehicles became involved in a chain reaction of collisions as drivers were unable to respond to the suddenly changed road conditions and the vehicles that had braked abruptly ahead of them.
Anatomy of a multi-vehicle crash
On the day in question, black ice suddenly formed on the E18 highway—a particularly treacherous phenomenon as road conditions can shift from normal to extremely slippery within a very short stretch of road. Several cars, many carrying families heading to winter vacation activities, began to skid upon entering the icy section. Despite attempts to brake, many drivers could not avoid colliding with vehicles ahead that had already slowed or stopped completely.
Those traveling further back in the traffic flow had minimal warning, and by the time they saw the problem ahead, it was often too late to react. The result was a multi-vehicle collision involving numerous vehicles and resulting in several injuries.
Understanding black ice
Black ice is one of winter's most unpredictable road hazards. It typically forms when the road surface is moist and the temperature rapidly drops below freezing, creating an almost instantaneous ice coating. What makes black ice particularly dangerous is that:
For a driver traveling at normal highway speeds, reaction time and braking distance can become insufficient when black ice suddenly appears.
Technology solutions: Connected Vehicle Systems
Systems that could potentially prevent similar accidents in the future include connected vehicle technologies that use data from vehicles already on the roads to detect and warn of dangerous road conditions in real-time. One such system is NIRA Dynamics' Road Surface Alerts, though similar technologies are being developed by various companies and research institutions.
How these systems work
Connected road safety systems collect data from sensors already present in modern cars, such as wheel speed sensors, accelerometers, and gyroscopes. By analyzing how a car's tires interact with the road surface, these systems can identify changes in friction that indicate slippery conditions. Detection can be done also when the car is not noticeably slipping. When one car detects a slippery section, this information is sent directly to a cloud-based system that can warn other vehicles in the area.
The innovative aspects of such systems include:
This allows cars to communicate with each other and with traffic infrastructure to create a "collective awareness" of road conditions. It allows drivers to adapt their speeds to suit the road conditions better.
Prevention possibilities
If connected road surface monitoring technology had been widely implemented on the day of the Uppsala crash, the sequence of events might have unfolded differently:
Potentially, the entire chain reaction of collisions could have been avoided or at least significantly reduced in scope.
The video shows how slippery roads are detected long before the first accidents occur. That is when the warnings could potentially go out, warning drivers about extremely slippery conditions on a specific location.
Future outlook and challenges
Despite the obvious potential, there are still challenges for widespread implementation of connected road condition alert systems:
Nevertheless, even limited implementation in 10-15% of the vehicle fleet could provide significant safety benefits for all road users.
Alternative preventive measures
While connected vehicle systems offer comprehensive solutions, several other technologies and approaches could also help prevent or mitigate similar accidents:
All of them could have been a part of minimizing the accidents, but they all have some limitations. The ABS braking data alerts and stationary vehicle warnings only provide warnings after vehicles have already encountered hazardous conditions and begun emergency braking. They are reactive rather than preventive but could still reduce the severity of chain-reaction crashes.
Adaptive speed signs based on road conditions are good, but costly, in terms of infrastructure needed, and they need some sort of data input.
Doing targeted road treatment on certain road stretches requires significant planning and infrastructure investment but can be cost-effective for known problem areas. These often go hand in hand with RWIS stations, but the number of weather stations is quite limited and increasing the number is costly.
Driver education and awareness campaigns can have a long-term effect, but the effectiveness depends on driver compliance.
Conclusion
The multi-vehicle crash outside Enköping serves as a reminder of how quickly traffic situations can deteriorate under winter conditions. It also highlights the need to implement available technology that can prevent similar accidents in the future.
Connected road safety systems represent a paradigm shift in traffic safety, where vehicles are no longer isolated units but parts of an interconnected network that together create a safer traffic environment. Already today, they are available in some vehicle models and the data is also made available to Departments of Transportation to improve winter maintenance efforts.
As we look toward increased electrification and automation of traffic, technologies like these will play an increasingly important role in preventing accidents and saving lives on our roads. Perhaps it is time for authorities, insurance companies, and vehicle manufacturers to jointly accelerate the adoption of such systems—because next time, we might not be fortunate enough to avoid an even worse scenario.