Mexico City license-plate driving restriction

Mexico City license-plate driving restriction assigned drivers a weekday on which they could not use their cars, based on the final digit of the license plate. The book contrasts this blunt restriction, introduced in Mexico City in an effort to curb air pollution, with Singapore’s congestion pricing: the restriction did little to reduce traffic because it did not give drivers a reason to seek alternatives on the days they were still allowed to drive, and some bought second cars to evade it.

Rule and Schedule

The restriction divided drivers into weekday groups according to their plates. A plate ending in 5 or 6 meant that the car could not be driven on Monday; 7 or 8 meant Tuesday; 3 or 4 meant Wednesday, with the same rotation continuing through the remaining weekdays. Everyone could drive on Saturday and Sunday. The rule therefore controlled access by day of the week, rather than charging for the use of a congested road at the time a driver chose to use it.

Evasion and Limited Effect

The restriction did not substantially reduce traffic. Drivers were not given an incentive to choose alternatives on the six days a week when they could drive, and some residents responded to their assigned off-days by buying second cars. The workaround exposed a weakness in the rule’s design: it limited a particular vehicle on a particular day without making driving itself costly across the week.

Contrast with Congestion Pricing

Singapore’s alternative left the decision to drive with each individual but made the price of entering a pay zone apparent. Its system charged for road use and, through electronic payment, made the cost immediate. The book treats this difference as consequential: rather than prohibiting specified drivers on specified days, pricing asks drivers to weigh the cost of a trip and allows the combined effect of those individual choices to shape traffic. The comparison presents the Mexico City restriction as a case where a categorical rule failed to elicit alternatives, while a price-based system sought to influence behavior without dictating who could drive.