Price signals and infrastructure change how people move.
Transportation has three well-replicated results: congestion pricing reduces traffic reliably, bus rapid transit increases ridership when it offers genuine speed improvements, and cycling infrastructure increases cycling proportionally to safety improvements. The evidence on behavior change without infrastructure or price changes is weaker.
6
experiments
6
positive results
0
null or negative
4
replicated
Key Findings
01
Congestion pricing consistently reduces traffic in charge zones — by 20–30% — across different cities, pricing levels, and implementation designs.
London's Congestion Charge (2003), Stockholm's congestion tax (2006), and Milan's Area C charge (2012) all found traffic reductions of 20–33% in the charge zone. Stockholm's temporary trial design provided a uniquely clean experiment: when the charge was removed, traffic returned to baseline levels, and when it was reinstated, traffic fell again. The mechanism — raising the price of peak-period driving — operates consistently across very different urban contexts. Revenue recycled into transit improvements further increases the mode shift effect.
02
Bus rapid transit produces significant ridership increases when it provides genuine speed improvements — but not when it is 'BRT in name only.'
Bogotá's TransMilenio — a full-specification BRT system with dedicated lanes, station-based boarding, and level boarding — produced large ridership increases and became one of the most studied transit systems in the world. London's bikeshare system increased cycling significantly among users, with health co-benefits. The evidence on half-measures — mixed-traffic bus lanes, non-level boarding — is much weaker. The implementation quality of BRT determines whether it actually delivers speed improvements that attract riders.
03
Plastic bag charges produce large and rapid reductions in bag usage — demonstrating that small price signals change high-frequency low-salience behaviors.
The UK plastic bag charge — 5p for a plastic bag at supermarkets — reduced plastic bag usage by 95% in major supermarkets within one year. The effect was dramatically larger than any awareness campaign had produced. Similar charges in Wales, Scotland, and other countries produced comparable effects. The mechanism is twofold: the price itself creates a financial disincentive, and the transaction makes the bag salient — changing a mindless habit into a deliberate choice.
All Experiments in the Registry
London Congestion Charge
positiveLondon, UK · 2003
5p Plastic Bag Charge
positiveEngland, UK · 2015
Stockholm Congestion Pricing Trial
positiveStockholm, Sweden · 2006
Bogotá TransMilenio BRT System
positiveBogotá, Colombia · 2000
London Cycle Hire Health Outcomes
positiveLondon, UK · 2012
Milan Area C Congestion Charge
positiveMilan, Italy · 2012
What the Evidence Cannot Yet Tell Us
What is the long-run effect of congestion pricing on urban form — does it shift development and housing demand, or do traffic patterns re-equilibrate over time?
Does BRT produce economic development effects comparable to light rail, or does the higher-quality infrastructure of rail drive location decisions that BRT cannot match?
What level of cycling infrastructure investment is required to produce a step-change in cycling mode share in car-dependent cities?
How do congestion pricing revenues need to be spent to maximize mode shift — in transit improvements, in congestion zone improvements, or returned to all residents?