Why Bangkok wants six-wheeler trucks off the roads during smog spikes

City authorities plan to expand Bangkok’s Low Emission Zone (LEZ) in 2026, significantly expanding a scheme that restricts the movement of high-polluting vehicles when air quality deteriorates. 

The proposal was discussed at a meeting chaired by deputy governors Jakkapan Piwngam and Tavida Kamolvej on December 19.

At the heart of the plan is PM2.5 — fine particulate matter small enough to enter the bloodstream — which regularly surges in the capital during the dry season. 

Officials said six-wheeler and larger trucks contribute disproportionately to these pollution peaks, particularly when weather conditions trap emissions over the city.

Under the proposed rules, trucks with six or more wheels would be barred from entering designated districts when PM2.5 levels reach hazardous thresholds. The ban would be triggered when pollution readings move into the “red zone,” defined as more than 75.1 micrograms per cubic metre, in at least five districts, with a two-day advance warning.

If PM2.5 levels reach orange or red in multiple districts and the ventilation rate falls below 3,000 square metres per second, the Bangkok Metropolitan Administration (BMA) would issue a citywide notice.

Officials said the system is designed to be responsive rather than permanent, allowing economic activity to continue while acting decisively during pollution emergencies. Forecasts, wind direction and other environmental factors will be factored into decisions on when to activate the ban.

The proposal builds on a pilot LEZ scheme tested earlier this year around the Ratchadaphisek Ring Road. During the trial, only trucks registered under the city’s “Green List” — alongside electric, natural gas and EURO 5–6 vehicles — were allowed to enter the zone.

In 2025 alone, nearly 58,000 six-wheeler and larger vehicles were registered under the Green List programme, underscoring both the volume of heavy traffic and the potential impact of tighter controls.