CAMBRIDGE, Mass. – More than 2,200 Americans a year die prematurely due to exposure of fine particulate matter in fuel emissions while idling in traffic.

According to new research by the Harvard Center for Risk Analysis at the School of Public Health the related public health cost was at least $18 billion.

However, the study also noted that because of cleaner trucks and cars out on the roadways, the number of additional premature deaths and public health costs has been declining over the past 10 years and will continue to do so over the next 20 years.

The study – published in the journal Environmental Health, is said to be the first to attempt to quantify the public health implications of growing traffic congestion.

The estimates, the researchers point out, are "likely conservative," as the study only details the impacts in high-traffic 83 urban areas, including the three highest: Los Angeles/Long Beach; New York City/New Jersey; and Chicago/Northern Indiana.

Researchers forecast traffic congestion will rise more than 30 percent over the period 2000 to 2030 in 18 urban areas.

The study noted some potential strategies to mitigate the health impact such as better traffic management through congestion pricing, traffic light synchronization and more efficient response to traffic incidents, and adding new highway and public transit capacity.