Methodology for assessing emission reduction of truck-only toll lanes

The emissions of carbon dioxide (CO2), the largest component of greenhouse gases (GHG) emissions, emitted from heavy trucks is second only to passenger cars in terms of GHG emissions from the transportation sector. Truck-only toll (TOT) lanes have been proposed in several cities as a means of improving truck flows and reducing freeway congestion. This paper describes an analysis that utilized the US EPA's MOBILE6.2 vehicle emissions modeling software to identify freeway locations with large pollutant emissions and estimated the changes in emission associated with TOT lanes. Emissions including hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), and CO2 were estimated by multiplying vehicle kilometers traveled by emission factors associated with various vehicle types and average speeds. The CO2 calculation was limited due to lack of sensitivity in the model of speed variation, which is one of the benefits of the implementation of TOT lanes. Mechanical equations of engine horsepower involving the change in vehicle speeds is applied to estimate the change in CO2 fuel consumption and then converted to estimate the change in CO2 emissions. The results show that voluntary and mandatory use of TOT lanes would reduce total CO2 emissions on all freeway lanes by 62% and 60%.