School Bus Idling Dangers: Myth or Fact?

October 04, 2012 | Written By:

Photo by @ bsabarnowl

It’s back to school time, which also means that more school buses are back on the road. An estimated 25 million children ride school buses every day. But when school buses idle with children on board or nearby, the resulting pollution can be harmful to kids’ growing bodies. In sufficient concentrations and duration, these pollutants can even increase the chance of serious health effects such as asthma. Our friends at the EPA have pulled together a “myth-busting” list of facts and encourage us all to test our knowledge of school bus idling.

Myth #1:
It is important to warm up engines with a long idle period, especially in cold weather.

For today’s school bus engines, bus and engine manufacturers routinely suggest a warm up time of less than five minutes.

Myth #2:
It is better for an engine to run at low speed (idling) than to run at regular speed.

Running an engine at low speed causes twice the wear on internal parts as driving at regular speeds.

Myth #3:
The engine must be kept running in order to operate the school bus safety equipment (flashing lights, stop sign). It is impossible to run this equipment off the internal circuitry of the bus because the battery will run down.

By re-wiring circuitry, safety equipment can be operated without the engine running for up to an hour with no ill-effects on the electrical system of the bus.

Myth #4:
Idling is necessary to keep the cabin comfortable.

Depending on the weather, many buses will maintain a comfortable interior temperature for some time without idling. Idling is not an efficient way to keep the cabin warm. Bus routes should be timed so children and drivers do not need to spend a lot of extra time on the bus when it is not en route, particularly in hot or cold weather. In addition, auxiliary heaters can be purchased and installed to keep the cabin comfortable.

Myth #5:
It is better to just leave the engine idling because a “cold start” produces more pollution.

recent EPA study found that the emissions measured after a schoolbus is restarted contains less carbon monoxide, nitrogen oxides and other pollutants than if the school bus idled continuously over a 10-minute period. The analysis indicated that continuous idling for more than three minutes emits more fine particles (soot) than a restart.

For more information about school bus idling, including EPA’s Clean School Bus program, visit

Read on! An HSC intern researches the dangers of school bus idling in this post.

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