WASHINGTON — The US DOT recently highlighted half a dozen strategies the government is considering to reduce greenhouse gas output from transportation, and trucking in particular.

Exhaust pipe emissions are said to contribute almost 30 percent of carbon greenhouse gases, DOT said in a report to Congress published late last month.

Most of those emissions, almost 80 percent, come from cars. Trucks contribute most of the remaining 20 percent, although the DOT notes that since the emergence of just-in-time shipping, among other factors, trucking’s contribution to GHGs has increased in the last 20 years.

Between 1990 and 2005, carbon dioxide emissions per ton-mile increased almost 13 percent, while ton-miles grew 58 percent, according to the DOT.

"These changes were driven by an expansion of freight trucking after economic deregulation …, widespread adoption of just-in-time manufacturing and retailing practices (that increased) highway congestion; and structural changes in the economy that produce higher-value, lower-weight, and more time-sensitive shipments better served by trucking," DOT said.

The 605-page report looks at several policy options. Promoting more use of low-carbon fuels such as biodiesel and improving fuel economy are two initiatives being considered.

Other strategies include lowering speed limits, reducing congestion at bottlenecks by adding capacity and traffic management, and cutting down on "carbon-intensive travel," which could be achieved by raising fuel taxes, charging drivers by the mile and expanding transit services and non-highway modes of transporting goods.

The sixth and most controversial strategy is cap-and-trade legislation to increase the cost of energy.

The plan is championed by the Obama administration and many Democratic legislators. Many businesses, including trucking carriers, strongly oppose the idea.