The National Renewable Energy Laboratory (NREL) has published a new report that found that Proterra’s battery-electric buses are nearly four times more fuel-efficient than comparable compressed natural gas (CNG) buses.

The study focuses on a pilot project for California’s Foothill Transit, in which 12 Proterra e-buses logged nearly 400,000 miles of on-road testing. The NREL team found that the battery-electric buses (or BEBs, in bureaucrat-speak) demonstrated average efficiency of 2.15 kWh per mile, which translates to about 17.48 miles per diesel gallon equivalent (DGE). The NABI CNG buses used for comparison had an average fuel economy of just 4.51 DGE.

The Proterra e-buses were also more reliable than their CNG ancestors, logging 133,000 miles between road calls (yes, MBRC), while the baseline CNG buses had an MBRC of about 45,000, which NREL said is “expected” for a new CNG vehicle.

The BEBs were on the road an average of 13.2 hours per day, receiving a 20 kWh recharge about 13 times a day.

While the BEBs trounced the CNGs in both DGE and MBRC, they also have a substantially higher up-front cost (UFC [OK, I just MTOU {made that one up}]): $904,000 apiece, compared with $575,000 for the CNG buses.

Source: National Renewable Energy Laboratory via Next-Gen Transportation