The Paradox of Traffic Bottlenecks: When Narrowing Streets Can Speed Things Up

Imagine you're stuck in traffic, watching cars inch forward through a construction zone that narrows the road to one lane. Your instinct might be to curse whoever created that bottleneck. But what if that narrow spot was actually helping you get home faster?

That's the counterintuitive finding from a new study by Victor Knoop, a traffic researcher at TU Delft in the Netherlands. Knoop created a mathematical model to understand how bottlenecks — places where streets narrow to a single lane — affect traffic flow. His results, published in July 2026 on the preprint server arXiv, turned out to be full of surprises.

Most people assume that adding more narrow points to a street would just create more places for traffic to get stuck. But Knoop found the opposite can be true. When he analyzed streets with multiple bottlenecks using what's called "directional priority" — where one direction of traffic gets to go first at each narrow point — he discovered something unexpected. The street could actually handle more cars than if it had just one bottleneck.

"Curiously, these capacity points are often above the capacity boundary of a street with a single FIFO or DP bottleneck, indicating that an extra bottleneck can increase capacity," Knoop wrote in his paper.

The study compared two different ways of managing bottlenecks. In the first approach, called FIFO (first-in-first-out), cars from both directions take turns fairly, like people lining up at a store. The second approach gives one direction priority — picture a narrow bridge where cars going one way get the lane entirely before the other side goes.

Under everyday, low-traffic conditions, the fair approach worked better. Streets with FIFO bottlenecks created less waiting time for drivers compared to streets where one direction always had priority. But when traffic got heavy and balanced from both directions, the priority system pulled ahead — it could squeeze more total cars through the same space.

Knoop also found that longer streets with multiple bottlenecks typically achieved higher capacities than shorter ones. All of this runs counter to what many city planners might assume about traffic design.

The research matters because cities around the world are constantly trying to balance safety, speed, and the number of vehicles moving through their streets. Construction zones, narrowed intersections, and shared-use streets are becoming more common as urban planners try to calm traffic and make neighborhoods more walkable. If narrowing roads can actually improve traffic flow under certain conditions — rather than just slow things down — it changes how engineers might approach street design.

The findings suggest there's no one-size-fits-all answer to traffic management. What works best depends on how busy the street usually is, how cars are directed through narrow points, and even the length of the road itself. For frustrated commuters, though, the takeaway might be simple: that orange cone line you're dreading could be doing more good than you think.