Emissions from restarting can be higher or lower than idling [1] • Idling for more than 10 seconds uses more fuel and emits more CO2 than engine restarting. •

Emissions from restarting can be higher or lower than idling [1] • Idling for more than 10 seconds uses more fuel and emits more CO2 than engine restarting. • Idling fuel usage varies from 0.2 to 0.5 gal/h for passenger vehicles across a range of sizes, and increased with idling speed. • NOx and THC emissions from restarting are larger, but at least an order of magnitude lower than those from starting a cold engine. • For short stops, it makes sense to turn the vehicle off in order to minimize fuel use and CO2 emissions. At least for the conditions evaluated in this work, the penalty in terms of criteria pollutant emissions [1] https://afdc.energy.gov/files/u/publication/which_is_greener.pdf https://afdc.energy.gov/files/u/publication/which_is_greener...