Electric Bus fleet reduces per mile energy ($0.09/mile) and propulsion only maintenance costs ($0.05/mile) when compared to a clean natural gas fleet.
The National Renewable Energy Laboratory (NREL) compared Foothill Transits electric bus and CNG fleet operation over a two-year period.
Los Angeles, California, United States
Foothill Transit Battery Electric Bus Demonstration Results: Second Report
Summary Information
In March 2014, Foothill Transit, located in the San Gabriel and Pomona Valley region of Los Angeles County, California, began operation of 12 electric buses within their fleet of clean natural gas (CNG) buses. In collaboration with California Air Research Board (CARB) and the U.S. Department of Energy (DOE) National Renewable Energy Laboratory (NREL), the agency performed an evaluation of the electric buses. NREL provided a third-party evaluation of the battery electric buses compared to the CNG buses in operation between April 2014 and December 2016. This report reports the results from August 2015 to December 2016.
Methodology
Foothill Transit purchased 12 electric buses through the Federal Transit Administration (FTA) TIGGER Program in order to fully operate one route with electric buses. The buses are charged at the midpoint of the route with an overhead catenary charging system. NREL conducted the evaluation as an unbiased third party on behalf of CARB. For the evaluation, NREL chose to compare the 12 electric buses to eight CNG buses that were of the same model year and were the best matches for size, weight, and intended operation. The evaluation considered:
- Total mileage
- Average monthly mileage
- Availability
- Fuel economy
- Average speed
- Miles between roadcalls (total, propulsion system only, and energy storage system)
Maintenance costs
Findings
Looking at the average speed results of the CNG verse electric buses there is a large difference. This is because of the operating conditions; the electric buses ran only on a slower route (Line 291) that had the installed catenary charging system. While the CNG buses were randomly assigned routes that included high-speed and express lines with much high average speeds. NREL was able to use data from when the CNG buses ran on Line 291 for a much better comparison of operating characteristics. When this data was analyzed, the CNG buses had an average fuel economy of 2.1 miles per gasoline equivalent (mpdge) on Line 291. Comparing this to the electric bus fuel economy of 17.35 mpdge, the electric bus is almost 8 times more efficient.
NREL used the average fuel economy to estimate per mile fuel costs (electricity or CNG). With the reduced fuel economy, the CNG buses would cost $0.50 per mile and the electric bus $0.41.
| Data Item | Electric | Electric | CNG | CNG |
|---|---|---|---|---|
| Number of buses | 12 | 12 | 8 | 8 |
| Data period | 4/14–7/15 | 8/15–12/16 | 10/14–7/15 | 8/15–12/16 |
| Number of months | 16 | 17 | 10 | 17 |
| Total mileage in data period | 401,244 | 501,037 | 364,373 | 656,399 |
| Average odometer | 33,437 | 77,705 | 45,547 | 132,405 |
| Average monthly mileage per bus | 2,333 | 2,456 | 4,555 | 4,826 |
| Total operating hours | 47,462 | 58,497 | — | — |
| Availability (85% is target) | 90 | 90 | 94 | 93 |
| Fuel economy (kWh/mile or miles/ggea) | 2.15 | 2.17 | 4.04 | 3.89 |
| Fuel economy (miles/dgeb) | 17.48 | 17.35 | 4.51 | 4.34 |
| Average speed, including stops (mph) | 10.6 | 8.57 | 17.6 | 17.6 |
| Miles between roadcalls (MBRC) – busc | 9,331 | 6,180 | 45,547 | 29,165 |
| MBRC – propulsion system onlyc | 25,078 | 16,405 | 91,093 | 56,710 |
| MBRC – ESSd onlyc | 133,748 | 300,760 | — | — |
| Total maintenance ($/mile)e | $0.16 | $0.21 | $0.18 | $0.22 |
| Total maintenance ($/mile without tire costs) | $0.12 | $0.14 | $0.18 | $0.20 |
| Maintenance – propulsion system only ($/mile) | $0.02 | $0.02 | $0.08 | $0.07 |
a Gasoline gallon equivalent.
b Diesel gallon equivalent.
c MBRC data cumulative from the clean point of April 2014 through December 2016.
d Energy storage system.
e Work order maintenance cost.
