Anyone who often drives on the highway knows the picture: the right-hand lane remains largely empty, the middle lane is full, and on the left one drives just above the speed limit. The result? Difficult overtaking, drivers who get stuck, and vehicles that hang around in the blind spot for too long.
So the question makes sense: wouldn't it be better to introduce different speed limits per lane? Right for those who want to drive more quietly, left for those who want to pass quickly, and the middle as a mixed lane.
It sounds simple, but does it work? Research and experiments provide interesting insights.
The idea of a per-lane speed limit
Today, one uniform limit applies on a highway. In Flanders, that is usually 120 km/h. But that system does not always ensure smooth flow.
An alternative: Differentiated Per-Lane Speed Limits (DPLSL).
- Right lane → lower speed, for trucks and quiet traffic
- Middle lane → mixed traffic with the standard limit
- Left lane → higher speed to pass quickly and safely
In theory, this would order the flow of traffic and encourage drivers to turn right again after overtaking.
Research on speed limit per lane
1. Simulations are positive
International studies (including Liu & Shi , 2018*) show that DPLSL in simulations:
- reduces speed dispersion,
- reduces the number of dangerous lane changes,
- and traffic safety improves.
* A 2019 study by Liu & Shi used a traffic simulation model to examine what happens when each lane has its own speed limit. Especially in a complex system with minimum and maximum speeds per lane, speed dispersion and the number of dangerous interchanges decreased. But: this only works if drivers comply. With low compliance, the risks just increased, especially by overtaking on the right
Click here to view the study in. (Please note that full access may be limited).
So the idea works on paper and in computer models.
2. Field test in Alaska
A study on the Seward Highway in Alaska examined the effect of differential speed limits on passing lanes: 65 mph (±105 km/h) in the left lane and 55 mph (±89 km/h) in the right lane. Analysis of traffic counts as well as surveys of 465 drivers showed that actual driving speeds often exceeded the allowable limits, especially in the right lane.
Moreover, drivers often estimate their own speed to be lower than it actually was. That difference between perceived and actual speed makes enforcement and safety especially challenging. The researchers conclude that more focus is needed on awareness and technology, such as feedback signs or telematics, to improve compliance and road safety.
(read the full paper on ResearchGate)
3. Differentiation by vehicle type.
In Montana, USA, a higher limit for passenger cars and a lower limit for trucks was in place for many years. However, practice showed that this system was not necessarily safer or more efficient. The difference in speed between vehicles sometimes just created more tension on the road.
You can compare it to what we see on bike paths today: classic bikes, e-bikes, speedpedelecs and scooters all ride together, but often at very different speeds. This creates unexpected situations, overtaking maneuvers and conflicts. The same risk exists on the highway when speed differences become too great between vehicle types.
4. Variable speed limits (VSL).
Active traffic management systems are already in place in Belgium, Germany, the UK and Canada. Through digital signs, the limit is adjusted according to traffic density or weather conditions. This is not per lane, but it is a flexible way to keep speeds homogeneous and safe.
Challenges in lane-by-lane speed limits
So why is DPLSL not yet massively implemented?
- Compliance: How do you make sure everyone maintains the right speed in the right box?
- Enforcement: Additional complexity for police and cameras.
- Risk of confusion: Too many different rules can make drivers uncertain.
The key: smart technology
With the rise of connected vehicles, ADAS and fleet management software, compliance is becoming increasingly realistic.
- A vehicle can receive automatic speed advice by lane via telematics.
- Dashboards and data analytics can monitor and report on driving behavior.
- For companies with large fleets, this provides an opportunity to coach drivers toward safe, efficient driving.
In short, what seems experimental today may be supported tomorrow by technology already present in many commercial vehicles.
Conclusion: future of per-lane speed limits
A highway where each lane has a different speed limit: it may sound futuristic, but the idea has strong foundations. Simulations show benefits, practical tests give hope, and with modern telematics, compliance is increasingly possible.
At AllConnects, we believe that data and innovation are key to making complexity simple. This kind of insight shows how traffic can become safer and more efficient, and how fleet management can play a crucial role in that.
What do you think? Is it time to make our highways smarter with differential speed limits?
Curious about other ways to improve road safety? Contact us and read our blog here about dashcams in fleet management - a practical solution to better protect both drivers and other road users.
Hilde Lavrijssen
Marketing Manager — AllConnects BV
Hilde closely follows Belgian legislation on mobility, fleet management, and time tracking and translates it into practical insights for companies in the transportation industry.
