Illustrative scenario
What if Mexico City took a scaled approach to “Hoy No Circula”?
Starting point · documented
A high-altitude basin traps pollution, and ozone episodes still trigger emergency restrictions.
The intervention · documented
Hoy No Circula
Driving restrictions based on licence plate and vehicle emissions.
Reduces traffic emissions, particularly from older vehicles.
Schematic direction of change
Air quality tends to respond relatively quickly once emissions fall, although weather and regional sources still drive episodes.
Causes this could address
- Vehicle emissionsA large vehicle fleet emits ozone precursors.
- Basin topography and altitudeMountains and inversions limit dispersion; strong sunlight drives photochemistry.
Impacts that could ease
- Respiratory health effectsOzone irritates airways and aggravates asthma.
- Activity restrictionsContingency phases restrict driving and outdoor activity.
Wider reach at higher intensity is an assumption of this illustration.
How change might unfold
Near term
Visible changes near targeted sources, especially where monitoring is dense.
Medium term
Fewer severe episodes if reductions cover the main local and regional sources.
Long term
Health benefits accumulate as long-term exposure falls.
Faded stages are less likely to be reached at scaled intensity.
What this would not change
Pollution transported from outside the area, and seasonal meteorology, remain beyond local control.
What it depends on
- Sustained funding and institutional capacity
- Consistent enforcement and monitoring
- Local stakeholder support
- Participation of affected communities
ILLUSTRATIVE SCENARIO — NOT A SCIENTIFIC PREDICTION. Built from documented causes, impacts and solutions plus general qualitative patterns. It contains no modelled numbers.