Natural gas-fueled buses and trucks: Will the climate really benefit?

Jonathan Camuzeaux

At a time when companies and governments are looking more closely at alternative fuel sources to reduce their environmental impact, many players in the transportation sector are considering shifting their bus or commercial truck fleets from diesel to natural gas fuel.  

They’re looking for an advantage in carbon dioxide (CO2) emissions as well as fuel costs savings to justify the higher vehicle costs and reduced fuel efficiency of natural gas vehicles.

Climate benefits uncertain at best

They may be surprised to know, however, that natural gas-powered vehicles are not necessarily more climate-friendly than their diesel fumes-spewing counterparts.

To make sure a fuel switch brings immediate climate benefits, we must make engine-efficiency improvements and major cuts in potent heat-trapping methane emissions along the natural gas value chain. If these steps are not taken, moving truck fleets from diesel to natural gas could actually increase warming for decades to come.

This is a growing concern today as the market share for such vehicles seems poised to grow.

While only about 3 percent of new freight trucks run on natural gas today, some analysts suggest their market share could reach as high as 20 percent over the next decade if high oil and diesel prices return. Meanwhile, investments in natural gas-powered utility vehicles and transit buses are growing, with 11 percent of such vehicles already running on gas.

It means we must address the problem of methane emissions today, before market penetration becomes significant and the technology is locked in and harder to change.

Natural gas value chain full of leaks

Methane – the main ingredient in natural gas and a greenhouse gas many times more potent than CO2 – is leaked to the atmosphere from the point where it’s first extracted from the ground to when it’s burned by a vehicle barreling down the expressway.

While natural gas releases less CO2 than diesel to the atmosphere when it is combusted, methane leaks from the production and transportation of natural gas has the potential to remove some or all of the climate benefits companies are looking for as they upgrade their fleets.

Adding to the challenge, today’s natural gas truck engines can be as much as 15 percent less efficient than diesel engines. Consuming more fuel for each mile traveled also reduces their net pollution reductions.

The opportunity ahead

Emissions in the natural gas value chain therefore represent a rare opportunity to achieve significant, cost-effective reductions in overall greenhouse gas emissions. If, in addition to reductions in methane leakage, the efficiency gap can be closed, natural gas trucks will fare that much better compared to diesel.

Much depends on several policy mechanisms currently in play, which could improve the climate prospects for these new buses and trucks. The new policies include anticipated federal methane regulations and upcoming federal fuel efficiency and greenhouse gas standards for heavy trucks.

The proposed new standards for heavy trucks would bring welcome reductions of certain sources of methane emissions occurring at the vehicle level. While this will certainly help, reductions upstream are crucial to maximize the potential benefits of natural gas trucks – which is where the federal methane standards come in.

In the meantime, we need to use caution. Before we encourage the trucking sector to switch to natural gas fuel, the United States needs to act sufficiently to reduce emissions and improve natural gas engine efficiency.

If we don’t, we could go from bad to worse.