State Law Limits Idling of Diesel Vehicles


On June 9, 2006, Public Act 094-0845 was signed into law, which prohibits diesel vehicles of more than 8,000 pounds (heavy-duty trucks and buses) from idling for more than ten minutes per hour when they are parked. This law will reduce diesel emissions that contribute to poor air quality while limiting unnecessary idling that wastes fuel. On average, one hour of idling uses up to one gallon of diesel fuel. A truck that idles for six hours per day will waste about $8,250 of diesel fuel per year with diesel costing $5.00 per gallon. Excess idling also increases engine maintenance costs and shortens engine life.

The law took effect July 1, 2006, and it only applies in the Chicagoland area and in the St. Louis Metro-East region. Exemptions to the law are described below. Another Illinois law prohibits a person from leaving a vehicle unattended on a public roadway for any amount of time while the engine is running. This law applies statewide.

Diesel exhaust and air quality

Diesel trucks and buses account for approximately 50 percent of the particulate matter (PM) and oxides of nitrogen (NOx) air pollution from on-road vehicles in Illinois. PM and NOx may contribute to a variety of health effects, including nausea, headaches, increased risk of asthma attacks, lung cancer, and premature death. Children and people with lung and heart conditions are generally the most sensitive to diesel exhaust. Millions of tons of air pollution are emitted every year in the U.S. by trucks and buses that idle while parked.

Affected counties

The new law only applies in areas that do not meet federal air quality standards, specifically:

Chicago area:

  • Cook County
  • DuPage County
  • Lake County
  • Kane County
  • McHenry County
  • Will County
  • Aux Sable and Goose Lake townships in Grundy County
  • Oswego Township in Kendall County

Metropolitan East St. Louis:

  • Madison County
  • St. Clair County
  • Monroe County

Special provisions for school buses and passenger buses.

The Illinois EPA recommends that school buses idle for no more than five minutes, and many schools have voluntarily adopted the five minute rule. Under the new law, parked buses may idle for up to ten minutes per hour when there are no passengers on board and fifteen minutes per hour to maintain passenger comfort (e.g., heat) while passengers other than the driver are on board. Exemptions may apply (see below).

The health of school children, bus drivers and those in the school building may be affected by idling school buses. School, business, and local government fleets may download additional information on idling at or request a packet of idle-reduction materials to be mailed to them by calling (217) 557-1441.

Applicability to diesel passenger cars and light-duty trucks

Nearly all diesel-powered passenger cars and light-duty trucks have a gross vehicle weight rating below 8000 pounds and, therefore, are exempt.

Other exemptions from the ten minute limit

  • When the outdoor air temperature is below 32 degrees or above 80 degrees.
  • When idling is necessary to operate equipment to prevent a safety or health emergency; for maintenance, repair, etc., or to operate auxiliary equipment.
  • Idling due to traffic congestion, loading/unloading, or mechanical difficulties.
  • When drivers are sleeping in a sleeper berth.
  • Exempt equipment includes:
    • Police, fire ambulance and other emergency/public safety vehicles used in an emergency capacity.
    • Airport ground support vehicles.
    • Armored vehicles when a person remains inside to guard the contents.
    • Certain farm vehicles.
    • A bus owned by a public transportation agency that is being operated on or between designated bus routes.
    • Vehicles owned by an electric utility that are running the engine to operate repair equipment.

Idling to ensure engine restart

Drivers sometimes idle diesel vehicles because there is a concern that the engine will not readily restart after being turned off. However, most diesel vehicles on the road today have technologies that allow for consistent restarts, even in cold weather. In fact, engine manufacturers recommend that engines be turned off to reduce fuel use and engine wear.


The idling law can only be enforced by state, county and local police and not the Illinois EPA. Voluntary compliance through education, outreach to affected drivers, and reports of excessive idling from citizens will all help to aid state and local police with enforcement of the law.


A violator could be fined $50 for a first offense and $150 for a second or subsequent offense within any 12-month period.

How to report excessive idling

Call the state, county or local police as they have the authority to enforce motor vehicle and traffic-related laws. Please do not contact the Illinois EPA to report excessive idling.