St. Louis County, MO Environmental Rules: Vehicle Idling Restrictions (2026)

340 of the County's Air Pollution Control Code opens with a broad nuisance ban: no person may permit the escape of soot, cinders, noxious acids, fumes, gases, or other particulate matter in a place or manner that endangers health, comfort, or safety, or damages property, and that escape is itself declared a public nuisance with each day of violation a separate offense. Subsection 2 targets vehicle exhaust specifically: no one may cause or permit a motor vehicle engine, other than an emergency vehicle, to idle for more than three consecutive minutes while parking, standing, or stopped as those terms are defined in the County Traffic Code.

The only carve-out is for engines that are actually powering a loading, unloading, or processing device, such as a refrigeration unit or a hydraulic lift, while the vehicle sits still. 390, which applies to any violation of the chapter not otherwise specifically penalized: up to a $1,000 fine, up to a year in the county jail, or both, with each day of continued violation counted as a separate offense. The County's Division of Air Pollution Control, part of the Department of Public Health at 801 South Brentwood in Clayton, handles enforcement and can also seek equitable relief in circuit court through the county counselor if a violator ignores a compliance order.

The rule reaches unincorporated areas and incorporated municipalities alike, since Chapter 612 does not carve out an exemption for cities the way the Animal Control Code does.