Foothill Transit Agency

Battery Electric Bus Progress Report

Data Period Focus: Jul. 2018 through Dec. 2018

Leslie Eudy and Matthew Jeffers

May 2019

NREL/PR-5400-72209
NREL | 2

Table of Contents

Introduction...................................................................3

Results Summary.......................................................... 4

Fleet Profile................................................................... 10

Evaluation Buses Specification................................... 11

Infrastructure Description........................................... 13

Data Summary...............................................................14

Route Assignments............................................16

Fleet Mileage Accumulation............................ 17

Availability Analysis........................................... 20

Fuel Economy and Cost Analysis..................... 27

Reliability—Miles Between Roadcall.............. 33

Maintenance Cost Analysis.............................. 35

Contacts......................................................................... 51

Acronyms and Abbreviations................................... 52

Appendix: Fleet Summary Statistics.......................... 54
NREL | 3

Introduction

This report summarizes results of a battery electric bus (BEB) evaluation at Foothill Transit, 

located in the San Gabriel Valley area of Los Angeles. Foothill Transit is collaborating with the 

California Air Resources Board and the U.S. Department of Energy’s National Renewable Energy 

Laboratory (NREL) to evaluate the buses in revenue service. The focus of this evaluation is to 

compare the performance and the operating costs of the BEBs to that of conventional technology 

buses and to track progress over time. Previous reports documented results from April 2014 

through June 2018.1,2,3,4 This report extends the data analysis through the end of 2018. The data 

period focus of this report is July 2018–December 2018. NREL plans to publish progress reports 

on the Foothill Transit fleet every 6 months through 2020.

1 Foothill Transit Battery Electric Bus Demonstration Results, NREL/TP-5400-65274, https://www.nrel.gov/docs/fy16osti/65274.pdf 2 Foothill Transit Battery Electric Bus Demonstration Results: Second Report, NREL/TP-5400-67698, https://www.nrel.gov/docs/fy17osti/67698.pdf

3 Foothill Transit Agency Battery Electric Bus Progress Report: Data Period Focus: Jan. 2017 through Dec. 2017, NREL/PR-5400-71292, 

https://www.nrel.gov/docs/fy18osti/71292.pdf

4 Foothill Transit Agency Battery Electric Bus Progress Report: Data Period Focus: Jan. 2018 through Jun. 2018, NREL/PR-5400-72207, 

https://www.nrel.gov/docs/fy19osti/72207.pdf
NREL | 4

Results Summary

Bus fleets: This evaluation includes 12 Proterra 35-ft fast charge buses (BEB 35FC), two Proterra 

40-ft Catalyst fast charge buses (BEB 40FC), and eight NABI 42-ft compressed natural gas (CNG) 

buses.

Bus use: The BEBs are operated on a 16-mile route (Line 291) that circles through the Pomona 

Transit Center (PTC) for charging. The average speed for this route is 10.6 mph. The CNG buses 

are randomly dispatched on all routes out of the operations facility, including higher speed 

commuter routes. The average speed for the CNG buses is 17.6 mph. This difference in duty cycle 

has an effect on the comparison of mileage, fuel economy, and costs per mile between fleets.

Availability: Availability in the second half of 2018 was 75.7% for the BEB 35FC buses, 75.0% for 

the BEB 40FC buses, and 90.1% for the CNG buses. The majority of unavailable time for the BEBs 

was due to general bus-related problems. Issues with the low-voltage batteries affected BEB 

availability. Other downtime resulted from issues with components such as transmission, air 

compressor, DC-DC converter, air conditioning, and the energy storage system (ESS).
NREL | 5

Results Summary (continued)

Fuel economy: From the beginning of the evaluation, NREL has collected miles and energy use 

from the Proterra data system on each bus. Over the last year, Proterra has been transitioning its 

data system to a new system to increase capability. During this transition, some data have been 

unavailable. In early 2018, Foothill Transit installed individual data loggers on each of its BEBs. 

NREL is using this data for calculating the fuel economy for the 35-ft buses. The data logger data 

is not yet available for the BEB 40-ft buses. 

BEB efficiency in the second half of 2018 was 2.18 kWh/mi (17.29 mpdge) for the BEB 35FC fleet 

and 3.63 mpgge (4.16 mpdge) for the CNG bus fleet. Because of the unavailable data for the BEB 

40FC buses, no fuel economy can be calculated for the most recent 6-month data period. The BEB 

fuel economy is approximately 4 times higher than that of the CNG buses as they are currently 

operated by Foothill Transit. NREL collected data on CNG buses operating on Line 291 that 

showed an average fuel economy of 2.09 mpdge (see previous report for details5). The BEB fuel 

efficiency is 8 times higher than that of the CNG buses in the same service.

5 Foothill Transit Battery Electric Bus Demonstration Results: Second Report, NREL/TP-5400-67698, https://www.nrel.gov/docs/fy17osti/67698.pdf
NREL | 6

Results Summary (continued)

Fuel cost: Based on energy purchased in the second half of 2018, the BEB fleet had a fuel cost of 

$0.46/mi (at $0.20/kWh) and the CNG fleet had a fuel cost of $0.28/mi (at $1.24/gge). The cost 

per unit of energy/fuel is the average for the data period of July 2018–December 2018. Because 

this 6-month data period includes more summer months when the electric rates are higher, the 

average cost per kWh is higher than the 6-month average from the previous report. For 2 out of 

the 6 months, the CNG cost increased due to disruptions in regional CNG supply, resulting in a 

higher average cost per gge than previously reported. To compare cost between buses in the 

same service, NREL estimated the cost per mile for the CNG buses if operated only on Line 291. 

An earlier analysis using data loggers to characterize the CNG bus operation on Line 291 resulted 

in a lower fuel economy of 2.09 mpdge.6 This lower fuel economy would increase the cost of the 

CNG buses to an overall average of $0.66/mi, which is slightly higher than the cost of the BEB 

fleet.

6 Foothill Transit Battery Electric Bus Demonstration Results: Second Report, NREL/TP-5400-67698, https://www.nrel.gov/docs/fy17osti/67698.pdf
NREL | 7

Results Summary (continued)

Maintenance cost: Cost to maintain the buses in the second half of 2018 was $0.78/mi for the BEB 

35FC buses, $0.74/mi for the BEB 40FC buses, and $0.46/mi for the CNG buses. The BEB 35FC bus 

cost has increased over what was reported previously. Several factors contributed to the high cost 

for the BEBs: 

• The BEB 35FC buses are now past the warranty period for the majority of components, 

resulting in higher parts costs, such as a DC-DC converter at ~$12,000 and a bus air compressor 

at ~$8,000. 

• All maintenance has been transitioned to on-site contractor staff, resulting in increased labor 

hours for training and troubleshooting as the staff become more familiar with systems and 

components. Total unscheduled labor on the BEBs has increased from 2017 to 2018. 

Unscheduled labor for the BEB 35FC buses increased from 72 hours per bus in 2017 to 130 

hours per bus in 2018—a 45% increase. Unscheduled labor for the BEB 40FC buses increased 

by 60%, from 51 hours per bus in 2017 to 128 hours per bus in 2018. By comparison, the CNG 

buses’ unscheduled labor increased by only 30%—79 hours per bus in 2017 to 113 hours per 

bus in 2018. 
NREL | 8

Results Summary (continued)

• Foothill Transit continues to have issues with the low-voltage batteries. NREL analyzed the 

data for low-voltage batteries for all three bus fleets. The BEBs averaged 7.8 changeouts per 

bus at approximately 12,000 miles between changeout. The CNG buses averaged 1.13 

changeouts per bus at more than 214,000 miles between changeout. One issue is that the 

accessories (farebox, cameras, etc.) continually draw power from these batteries. The CNG 

buses are equipped with an auto shutoff for the accessories; the BEBs are not. Proterra 

reports that it is working on an auto-shutoff feature for its new designs. The manufacturer 

will provide a retrofit for BEBs currently in service. Because this issue is not related to the 

BEB technology, NREL has provided the costs with and without the low-voltage battery 

replacement costs.

• Total maintenance cost without low-voltage battery costs was $0.70/mi for the BEB 35FC 

buses, $0.63/mi for the BEB 40FC buses, and $0.44/mi for the CNG buses.
NREL | 9

Results Summary (continued)

Future analysis: NREL will continue to collect data on the two existing BEB fleets in comparison to 

the CNG baseline fleet, and will add data from a fleet of 40-ft Proterra Catalyst E2 extended range 

buses. The new buses will be operated out of another depot and will be charged primarily 

through overnight depot charging. NREL will select another baseline fleet from this depot for 

comparison. 
NREL | 10

Fleet Profile

Foothill Transit serves a 327-

square-mile area covering the 

San Gabriel and Pomona Valley 

region of Los Angeles County. 

Foothill Transit’s administrative 

office is located in West Covina, 

California. Foothill Transit is 

governed by a Joint Powers 

Authority of 22 member-cities 

and the County of Los Angeles. 

Foothill Transit operates 36 local and express routes including commuter runs to downtown Los 

Angeles. The current bus fleet consists of 343 CNG buses and 16 BEBs.
NREL | 11

Evaluation Buses: Specifications

Vehicle System BEB 35FC BEB 40FC CNG

Number of buses 12 2 8

Bus manufacturer/model Proterra/BE35 Proterra/Catalyst Fast Charge NABI/BRT-07.03

Model year 2014 2016 2014

Bus purchase costa $904,490 $879,845 $575,000

Length/width/height 35 ft/102 in./129 in. 42.5 ft/102 in./134 in. 42 ft/102 in./137 in.

GVWR/curb weight 37,320 lb/27,680 lb 39,050 lb/27,000 lb 42,540 lb/33,880 lb

Wheelbase 237 in. 296 in. 308 in.

Passenger capacity 35 seats, 2 wheelchair 

positions, 18 standees

40 seats, 2 wheelchair 

positions, 18 standees

38 seats, 2 wheelchair 

positions, 10 standees

Motor or engine Permanent magnet, UQM, 

PP220 

Permanent magnet, UQM, 

PP220 CNG engine, Cummins, 8.9 ISL G

Rated power 220 kW peak (295 hp) 220 kW peak (295 hp) 280 hp @ 2,200 rpm

Energy storage (BEB)

Fuel capacity (CNG)

Lithium-titanate batteries, 

Altairnano, TerraVolt 368 

volts, 88 kWh total energy

Lithium-titanate batteries, 

Toshiba, TerraVolt 331 volts, 

106 kWh total energy

7 Type IV cylinders, 

22,204 scf at 3,600 psi 

Accessories Electric Electric Mechanical

Emissions equipment N/A N/A 3-way catalyst

Transmission/retarder Regenerative braking Regenerative braking N/A

a Includes amenities such as painting of bus and livery, surveillance system, PA system, radio, safety vision monitor.
NREL | 12

Evaluation Buses

BEB 35FC BEB 40FC

CNG 

Photo by Leslie Eudy, NREL

Photo by Leslie Eudy, NREL Photo courtesy of Foothill Transit
NREL | 13

Infrastructure Description

Foothill worked with the City of Pomona to establish an on-route fast charging station at the PTC. The station 

features two Eaton chargers in a climate controlled building with charge heads (right photo) positioned on either 

side (left photo). The two chargers operate as separate units with a dedicated control system for each. A 

common communication network serves both units with sensors to detect which charge head a bus is 

approaching to enable proper bus-to-charger communication for docking. The system is designed to fully charge 

a bus in under 10 minutes. For Foothill’s Line 291, typical charge times are around 7 minutes including docking 

time. Foothill built a layover time into the schedule to allow enough time for charging. Software controls prevent 

charging from surpassing the kWh limit that results in high demand charges. 

Photos by Leslie Eudy, NREL
NREL | 14

Data Summary: Total from Start of Service

a Miles per gasoline gallon equivalent d Energy storage system b Miles per diesel gallon equivalent e Work order maintenance cost c MBRC data cumulative from the clean point of April 2014 through end of current data period f See issue with the low-voltage batteries explained on slide 50 

Data Item BEB 35FC BEB 40FC CNG

Number of buses 12 2 8

Data period 4/14–12/18 1/17–12/18 10/14–12/18

Number of months 57 24 51

Total mileage in data period 1,449,320 93,418 1,932,057

Average odometer 110,825 38,067 217,943

Average monthly mileage per bus 2,183 1,946 4,735

Availability (85% is target) 86 80 96

Fuel economy (kWh/mile or mpggea

) 2.17 2.22 3.84

Fuel economy (mpdgeb

) 17.32 16.98 4.40

Average speed, including stops (mph) 10.60 10.60 17.60

Miles between roadcalls (MBRCc

)—bus 5,706 6,673 26,834

MBRCc

—propulsion system only 15,418 23,355 42,935

MBRCc

—ESSd only 241,553 — —

Total maintenance cost ($/mile)e 0.39 0.44 0.26

Total maintenance cost without low-voltage battery costs ($/mile)f 0.34 0.34 0.26

Maintenance cost—propulsion system only ($/mile) 0.11 0.16 0.10

Propulsion system maintenance cost without low-voltage battery costs ($/mile) f 0.06 0.07 0.09
NREL | 15

Data Summary: Jul.–Dec. 2018

Data Item BEB 35FC BEB 40FC CNG

Number of buses 12 2 8

Data period 7/18–12/18 7/18–12/18 7/18–12/18

Number of months 6 6 6

Total mileage in data period 145,281 20,067 226,981

Average odometer 110,825 38,067 217,943

Average monthly mileage per bus 2,018 1,672 4,729

Availability (85% is target) 76 75 90

Fuel economy (kWh/mile or mpggea

) 2.18 — 3.63

Fuel economy (mpdgeb

) 17.29 — 4.16

Average speed, including stops (mph) 10.60 10.60 17.60

Miles between roadcalls (MBRCc

)—bus 5,706 6,673 26,834

MBRCc

—propulsion system only 15,418 23,355 42,935

MBRCc

—ESSd only 241,553 — —

Total maintenance cost ($/mile)e 0.78 0.74 0.46

Total maintenance cost without low-voltage battery costs ($/mile)f 0.70 0.63 0.44

Maintenance cost—propulsion system only ($/mile) 0.32 0.42 0.25

Propulsion system maintenance cost without low-voltage battery costs ($/mile) f 0.24 0.30 0.23

a Miles per gasoline gallon equivalent d Energy storage system b Miles per diesel gallon equivalent e Work order maintenance cost c MBRC data cumulative from the clean point of April 2014 through end of current data period f See issue with the low-voltage batteries explained on slide 50 
NREL | 16

Route Assignments

Foothill Transit uses the BEB 35FC buses to fully electrify Line 291, which 

requires seven buses during peak hours. Line 291 is a 16.1-mile route 

between La Verne and Pomona that loops through the PTC in both 

directions. The average speed for the route is 10.6 mph. The agency 

adjusted the schedule to accommodate time for charging the buses. The 

additional buses are used as spares to allow for maintenance downtime 

and also as fill-in buses for other appropriate routes that go through the 

PTC, such as Line 855. The two 40-ft buses (BEB 40FC) are also used on 

these routes. In October 2017, Line 855 was eliminated. From that 

period on, the buses were operated only on Line 291.

The CNG buses are randomly dispatched on all routes out of Pomona 

Operations including commuter routes. Average speed for Pomona 

Operations as a whole is 17.6 mph.

Image courtesy of Foothill Transit
NREL | 17

BEB Fleet Total Miles

• Combined totals for 12 BEB 35FC buses and two BEB 40FC buses
NREL | 18

Fleet Average Monthly Miles by Bus: Jul.–Dec. 2018

Bus ID Miles Months Average Monthly 

Mileage

2200 25,733 6 4,289

2201 23,389 6 3,898

2202 31,071 6 5,179

2203 25,457 6 4,243

2204 28,932 6 4,822

2205 31,614 6 5,269

2206 31,353 6 5,226

2207 29,432 6 4,905

CNG Total 226,981 48 4,729

Bus ID Miles Months Average Monthly 

Mileage

2004 13,962 6 2,327

2005 9,853 6 1,642

2006 10,715 6 1,786

2007 11,889 6 1,981

2008 14,021 6 2,337

2009 13,395 6 2,233

2010 11,505 6 1,917

2011 14,006 6 2,334

2012 11,299 6 1,883

2013 8,542 6 1,424

2014 13,595 6 2,266

2015 12,498 6 2,083

BEB 35FC Total 145,281 72 2,018

2016 8,616 6 1,436

2017 11,451 6 1,909

BEB 40FC Total 20,067 12 1,672

The average monthly operating mileage per bus 

for the BEBs is less than half that of the CNG 

buses. This is a result of the planned operation of 

the buses, in which the CNG buses accumulate 

miles faster than the BEBs do, and does not 

indicate a specific limitation of the technology.
NREL | 19

Fleet Average Monthly Miles
NREL | 20

Availability Analysis

Availability, which is a measure of reliability, is presented as the percentage of days the buses are 

actually available out of days that the buses are planned for passenger service. Buses available for 

service may have been used in passenger service, training, or special events, or they may have 

been available but just not used. Buses unavailable for service may have had issues with the 

propulsion system (energy storage system, electric drive system), general bus maintenance, or 

issues with the charging system. Accidents are removed from the data—the bus is considered 

“not planned” during the repair time.

The data presented are based on availability for morning pull-out and don’t necessarily reflect allday availability. Transit agencies typically have a target of 85% availability for their fleets to allow 

for time to handle scheduled and unscheduled maintenance. For the Foothill Transit fleet, the 

buses are planned to operate every day, including weekends. For Foothill Transit, the source for 

availability data is garage activity sheets for the Pomona Operations, which list each bus that is 

not available for morning pull-out and provide a general reason for unavailability. These activity 

sheets are for the facility as a whole and include the BEBs as well as the CNG buses. The garage 

activity sheets are typically available for weekdays. 

NREL presents availability as a monthly average trend and as overall availability. Unavailable time 

is separated into several categories to show the primary reason for downtime. 
NREL | 21

Availability Summary: Jul.–Dec. 2018

Category BEB 35FC 

(# Days)

BEB 35FC 

(%)

BEB 40FC 

(# Days)

BEB 40FC 

(%)

CNG

(# Days)

CNG 

(%)

Planned work days 1,286 216 861

Days available 974 75.7 162 75.0 776 90.1

Unavailable 312 24.3 54 25.0 85 9.9

ESS 18 1.4 1 0.5 — —

CNG engine — — — — 65 7.5

Electric drive 36 2.8 20 9.3 — —

Charging issues 5 0.4 0 0.0 — —

Preventive maintenance 6 0.5 1 0.5 6 0.7

General bus maintenance 207 16.1 32 14.8 13 1.5

Transmission 40 3.1 0 0.0 1 0.1

• The per-bus availability for the BEBs ranged from a low of 57% to a high of 91%.

• The majority of unavailable time for the BEBs was attributed to general bus maintenance.

• Issues with the low-voltage batteries lowered availability for the BEBs (29% of general bus maintenance days for 

the 35FC BEBs and 47% of general bus maintenance days for the 40FC BEBs).

• The majority of unavailable time for the CNG buses was attributed to engine issues.

• General bus maintenance includes everything that doesn’t fall into one of the other categories.
NREL | 22

Monthly Availability: BEB 35FC Fleet

• The green line tracks the average monthly availability for the BEB 35FC fleet.

• The stacked bars provide the number of unavailable days by bus each month separated by six categories.

• Low-voltage batteries fall into the general Bus Maintenance category (green bars) and make up 29% of general 

bus maintenance unavailable days.
NREL | 23

Monthly Availability: BEB 40FC Fleet

• The blue line tracks the average monthly availability for the BEB 40FC fleet.

• The stacked bars provide the number of unavailable days by bus each month separated by six categories.

• Issues with the low-voltage battery during August 2017 lowered the availability (47% of general bus 

maintenance unavailable days). December availability issues were due to a traction motor inverter failure. 
NREL | 24

Monthly Availability: CNG Fleet

• The blue line tracks the average monthly availability for the CNG fleet.

• The stacked bars provide the number of unavailable days by bus each month separated by four categories.
NREL | 25

Overall Fleet Availability: Full Data Period
NREL | 26

Overall Fleet Availability: Jul.–Dec. 2018
NREL | 27

Fuel Economy Analysis

Proterra records and stores data—including total electrical energy used (kWh), number of charges, 

and miles driven—on each of the buses. These data were provided to NREL for calculating 

efficiency of the buses in kWh per mile. Foothill Transit’s CNG buses are typically fueled once each 

day. Foothill Transit provided individual fueling records for the CNG buses. CNG is typically tracked 

in units of gasoline gallon equivalent (gge). 

To compare the BEBs to the baseline buses, NREL converted the electrical energy from kWh to 

diesel gallon equivalent (dge) and converted the CNG fuel energy from gge to dge using the 

following conversion factors. 

Energy content of fuel (DOE Alternative Fuels Data Center: https://afdc.energy.gov/fuels/properties)

• Electricity: 3,414 Btu/kWh

• CNG: 112,114 Btu/gge (LHV)

• Diesel: 128,488 Btu/dge (LHV)

Conversion factors 

• Electrical energy to dge: 37.64 kWh/dge 

• CNG fuel energy to dge: 1.146 gge/dge

Btu: British thermal units; LHV: lower heating value
NREL | 28

Fuel Economy by Bus: Jul.–Dec. 2018

Bus ID Miles CNG

(gge) mpgge

Diesel 

Gallon 

Equiv. 

Fuel 

economy 

(mpdge)

2200 24,701 7,048.0 3.50 6,149.8 4.02

2201 20,665 6,169.9 3.35 5,383.7 3.84

2202 25,510 6,674.2 3.82 5,823.7 4.38

2203 20,145 5,332.4 3.78 4,652.9 4.33

2204 22,887 6,256.7 3.66 5,459.4 4.19

2205 25,585 7,018.0 3.65 6,123.7 4.18

2206 25,645 6,967.5 3.68 6,079.6 4.22

2207 22,640 6,307.3 3.59 5,503.5 4.11

CNG Total 187,778 51,774.0 3.63 45,176.1 4.16

Bus ID Miles Energya

(kWh) kWh/mi

Diesel 

Gallon 

Equiv. 

Fuel 

economy 

(mpdge)

2004 13,962 27,990.2 2.00 743.6 18.78

2005 9,853 21,026.4 2.13 558.6 17.64

2006 10,715 24,361.8 2.27 647.2 16.55

2007 11,889 26,838.6 2.26 713.0 16.67

2008 14,021 31,271.8 2.23 830.8 16.88

2009 13,395 29,301.3 2.19 778.5 17.21

2010 11,505 25,761.1 2.24 684.4 16.81

2011 14,006 28,856.5 2.06 766.6 18.27

2012 11,299 24,795.9 2.19 658.8 17.15

2013 8,542 17,706.1 2.07 470.4 18.16

2014 13,595 29,098.6 2.14 773.1 17.59

2015 12,498 29,267.6 2.34 777.6 16.07

BEB 35FC 

Total 145,281 316,276.0 2.18 8,402.7 17.29

2016 — — — — —

2017 — — — — —

BEB 40FC 

Total — — — — —

• The BEB fuel economy is 4 times higher than that 

of the CNG buses, as operated on current routes.

• Previous testing showed the CNG buses had a fuel 

economy around 2.09 mpdge on Line 291, which 

is 8 times lower than that of the BEBs.

• Insufficient energy data was received for the BEB 

40FC fleet to calculate 2018 fuel economy.

a Total energy consumed by the bus, does not include losses during charging 
NREL | 29

Fleet Average Monthly Fuel Economy

Overall Jul.–Dec. 2018

Fleet kWh/mi, mpgge mpdge kWh/mi, mpgge mpdge

BEB 35FC 2.17 17.32 2.18 17.29

BEB 40FC 2.22 16.98 — —

CNG 3.84 4.40 3.63 4.16

Jan-Feb energy data unavailable

2018 energy data unavailable
NREL | 30

Monthly Electric Utility Costs

• Data are based on utility billing periods, not calendar months

• Seasonal rates apply: average summer rate (Jun–Sep): $0.21/kWh; average winter rate (Oct–May): $0.16/kWh

• Average rate under TOU-GS-1-A rate structure: $0.17/kWh; average rate under TOU-EV-4 rate structure: $0.18/kWh

• Average rate for 2018 full calendar year: $0.19/kWh
NREL | 31

Monthly Average Fuel Price

• Electricity prices vary seasonally; CNG prices are consistent throughout the data period, but CNG prices 

increased in August 2018 and December 2018 due to temporary disruptions in regional CNG supply.

• CNG cost includes price of fuel, transmission, and operations and maintenance cost for station.

• On average, electricity cost is more than 6 times the cost of CNG.
NREL | 32

Fuel Cost Per Mile

Average 

Service Speed 

(mph)

Fuel 

Economy

(mpdge)

Overall

$/mi

Data Period

$/mi

BEB 35FC 10.6 17.32 0.45 0.46

BEB 40FC 10.6 16.98 0.45 0.46

CNG 17.6 4.40 0.23 0.28

CNG on Line 291 10.6 2.09 0.52 0.66

The operating duty cycle of a bus has a significant effect on fuel economy and therefore cost. 

Earlier in the evaluation, NREL collected drive cycle data on a selection of CNG buses that were 

operated on a variety of Foothill Transit routes including Line 291. On Line 291, the average fuel 

economy for the CNG buses was 2.09 mpdge. 

During the second half of 2018, Foothill Transit paid an average of $1.24/gge ($1.42/dge) for CNG. 

The average cost of electricity during the second half of 2018 was $0.20/kWh ($7.35/dge). The 

table provides the cost per mile for the BEBs and CNG buses as used by the fleet and estimates 

the cost per mile of the CNG buses if they were only operated on Line 291. The lower fuel 

economy would increase the CNG fuel cost to an average of $0.52/mi, which is slightly higher 

than that of the BEBs.
NREL | 33

Roadcall Analysis

A roadcall, or revenue vehicle system failure, is defined as a failure of an in-service bus that 

causes the bus to be replaced on route or causes a significant delay in schedule. If the problem 

with the bus can be repaired during a layover and the schedule is kept, it is not considered a 

roadcall. The analysis described here includes only roadcalls that were caused by “chargeable” 

failures. Chargeable roadcalls include systems that can physically disable the bus from operating 

on route, such as interlocks (doors, air system), engine, or things that are deemed to be safety 

issues if operation of the bus continues. They do not include roadcalls for things such as problems 

with radios, fareboxes, or destination signs.

The transit industry measures reliability as mean distance between failures, also documented as 

MBRC. NREL tracks MBRC by total bus roadcalls, propulsion-related roadcalls, and ESS-related 

roadcalls (for electric buses). Total bus roadcalls include all chargeable roadcalls. Propulsionrelated roadcalls is a subset of total roadcalls and includes all roadcalls due to propulsion-related 

systems including the battery system (or engine for a conventional bus), electric drive, fuel, 

exhaust, air intake, cooling, non-lighting electrical, and transmission systems. The ESS-related 

roadcalls—a subset of the propulsion-related roadcalls—and MBRC are included for the BEBs. 
NREL | 34

Cumulative MBRC

• The upper chart shows cumulative MBRC for all chargeable roadcalls.

• The lower chart shows MBRC for propulsion-related roadcalls.

• The ESS-related MBRC for the BEB 35FC fleet is 241,553.

• No ESS-related roadcalls have been recorded for the BEB 40FC fleet.
NREL | 35

Maintenance Analysis

NREL collects all work orders for the evaluation buses to calculate a maintenance cost per mile. Costs 

for accident-related repair, which are extremely variable from bus to bus, were eliminated from the 

analysis. Warranty costs are not included in the cost-per-mile calculations because those costs are 

covered in the capital cost of the buses. For consistency, NREL uses a constant $50 per hour labor rate. 

This does not reflect an average rate for Foothill Transit. Cost per mile is calculated as follows:

Cost per mile = [(labor hours * 50) + parts cost)] / mileage

NREL calculates total cost per mile, scheduled maintenance cost per mile, and unscheduled 

maintenance cost per mile. NREL also categorizes maintenance cost by system to provide insight into 

what systems have the most costs for each technology. The work orders are coded using vehicle 

maintenance reporting standards (VMRS) developed by the American Trucking Association to aid the 

industry in tracking equipment and maintenance using a common standard. 

The propulsion system costs are of particular interest. Propulsion-related vehicle systems include the 

exhaust, fuel, engine, battery modules, electric propulsion, air intake, cooling, non-lighting electrical, 

and transmission systems. These systems have been separated to highlight maintenance costs most 

directly affected by the different advanced propulsion systems for the buses. 
NREL | 36

Maintenance Analysis Results: Jul.–Dec. 2018 

Bus ID Mileage Parts ($) Labor 

Hours

Scheduled 

Cost

($/mi)

Unscheduled 

Cost

($/mi)

Total 

Cost 

($/mi)

2200 25,733 $6,737.04 115.1 $0.15 $0.34 $0.49

2201 23,389 $9,497.79 119.2 $0.11 $0.55 $0.66

2202 31,071 $4,523.21 92.7 $0.12 $0.18 $0.29

2203 25,457 $13,945.13 179.1 $0.08 $0.82 $0.90

2204 28,932 $6,477.17 107.5 $0.12 $0.29 $0.41

2205 31,614 $4,143.41 73.1 $0.13 $0.11 $0.25

2206 31,353 $5,420.07 126.2 $0.12 $0.25 $0.37

2207 29,432 $6,747.83 120.5 $0.12 $0.31 $0.43

CNG 

Fleet 226,981 $57,491.65 933.4 $0.12 $0.34 $0.46

Bus ID Mileage Parts ($) Labor 

Hours

Scheduled 

Cost

($/mi)

Unscheduled 

Cost

($/mi)

Total 

Cost 

($/mi)

2004 13,962 $2,440.28 108.4 $0.12 $0.44 $0.56

2005 9,853 $897.43 50.4 $0.09 $0.26 $0.35

2006 10,715 $3,522.45 158.5 $0.07 $1.00 $1.07

2007 11,889 $2,894.48 89.4 $0.08 $0.54 $0.62

2008 14,021 $3,174.09 90.5 $0.11 $0.44 $0.55

2009 13,395 $3,713.20 145.9 $0.09 $0.73 $0.82

2010 11,505 $2,930.04 86.6 $0.09 $0.55 $0.63

2011 14,006 $3,555.98 67.8 $0.11 $0.39 $0.50

2012 11,299 $15,847.70 87.6 $0.10 $1.69 $1.79

2013 8,542 $2,573.98 76.3 $0.08 $0.67 $0.75

2014 13,595 $1,967.96 90.8 $0.08 $0.40 $0.48

2015 12,498 $11,764.02 113.3 $0.11 $1.28 $1.39

BEB 35FC 

Fleet 145,281 $55,281.61 1,165.7 $0.09 $0.69 $0.78

2016 8,616 $1,157.84 164.05 $0.11 $0.98 $1.09

2017 11,451 $2,423.66 61.68 $0.09 $0.39 $0.48

BEB 40FC 

Fleet 20,067 $3,581.50 225.7 $0.10 $0.64 $0.74

Reasons for cost increase over previous report 

(BEB 35FC: $0.71/mi, BEB 40FC: $0.29/mi):

• Continued issues with the low-voltage batteries

• Issues with the bus air compressor 

• Replacement of one DC-DC converter

• Maintenance being transferred from OEM to 

contractor, which results in more labor hours

• Warranty ended for some systems.

OEM: original equipment manufacturer
NREL | 37

Monthly Scheduled and Unscheduled Maintenance 

Cost: BEB 35FC Fleet

• The warranty period has ended and transit staff are handling most of the maintenance work.

• Issues with the low-voltage batteries continue to result in increasing costs.

• DC-DC converter replacement (part cost >$12,000) increased November 2018 costs.

• Air compressor replacement (part cost >$8,000) increased December 2018 costs.
NREL | 38

Monthly Scheduled and Unscheduled Maintenance 

Cost: BEB 40FC Fleet

• Issues with the low-voltage batteries resulted in costs that were higher than expected.

• Because the fleet consists of only two buses, the cost per mile is more sensitive to cost increases.

• The average odometer trend for the BEB 40FC fleet is not included at this time.
NREL | 39

Monthly Scheduled and Unscheduled Maintenance 

Cost: CNG Fleet

• Higher scheduled costs during July 2015, April 2016, and November 2017 are caused by multiple buses 

reaching the mileage target for a major preventive maintenance (PM).

• Unscheduled costs in the last 8 months have risen primarily due to engine issues.
NREL | 40

System

BEB 35FC BEB 40FC CNG

Cost per 

Mile ($)

Percent 

of Total 

(%)

Cost per 

Mile ($)

Percent 

of Total 

(%)

Cost per 

Mile ($)

Percent 

of Total 

(%)

Cab, body, and accessories 0.317 41 0.417 56 0.248 54

Propulsion-related 0.121 16 0.126 17 0.039 9

PMI 0.092 12 0.101 14 0.059 13

Brakes 0.010 1 0.001 0 0.034 7

Frame, steering, and suspension 0.034 4 0.009 1 0.008 2

HVAC 0.009 1 0.009 1 0.008 2

Lighting 0.021 3 0.043 6 0.001 0

Axles, wheels, and drive shaft 0.002 0 0.034 5 0.010 2

Air, general 0.091 12 0.000 0 0.004 1

Tires 0.084 11 0.000 0 0.048 10

Towing charges 0.000 0 0.000 0 0.000 0

Total 0.782 100 0.741 100 0.459 100

Total w/o low voltage battery costs 0.70 0.63 0.44

Maintenance Cost per Mile by System: Jul.–Dec. 2018

• Propulsion-related repairs for the BEBs: low-voltage batteries, battery equalizer, cooling system, DC-DC converter

• Overall cost per mile without low-voltage battery costs for the BEB 35FC buses was 1.6 times higher than the CNG 

bus cost; cost for the BEB 40FC buses was 1.4 times higher than the CNG bus cost.

Color coding:

Highest cost

Second highest cost

Third highest cost
NREL | 41

Maintenance Cost by System: BEB 35FC Fleet

• Costs for the BEB 35FC fleet continue to increase since the warranty ended and transit staff are learning to 

repair all systems. 

• The primary driver for the higher propulsion-related cost was issues with the low-voltage batteries (see cost per 

mile by propulsion subsystem chart on slide 44).

• Replacement of a DC-DC converter in November 2018 resulted in high costs.
NREL | 42

Maintenance Cost by System: BEB 40FC Fleet

• Because the BEB 40FC fleet consists of only two buses, the cost per mile is more sensitive to cost 

increases.

• The high propulsion cost during August 2017 and August 2018 was primarily due to the low-voltage 

battery issue (see cost per mile by propulsion subsystem chart on slide 45).
NREL | 43

Maintenance Cost by System: CNG Fleet

• CNG bus maintenance cost shows an increase over time as the buses age and pass the warranty period.

• During the high-cost months, multiple buses reached the mileage for a major PM.

• Higher propulsion system costs in the last half of 2018 were due to tune-ups on multiple buses, exhaust 

issues, oil leaks, and engine control module failures.
NREL | 44

Propulsion System Maintenance Cost by Subsystem: 

BEB 35FC Fleet

• Low-voltage battery replacements fall into the cranking/charging category.

• Replacement of a DC-DC converter in June 2018 and November 2018 resulted in high costs in the electric 

drive category.
NREL | 45

Propulsion System Maintenance Cost by Subsystem: 

BEB 40FC Fleet

• Both buses in the BEB 40FC fleet had low-voltage battery changeouts in August 2017 and August 2018.

• High costs in September 2018 were due to labor to troubleshoot issues with a DC-DC converter.

• High costs in December 2018 were due to labor to replace the traction motor inverter; the part cost was 

covered under warranty.
NREL | 46

Propulsion System Maintenance Cost by Subsystem: 

CNG Fleet

• Increased costs in the last half of 2018 fall into several categories: 

o Exhaust system—exhaust gas recirculation, turbocharger, catalyst 

o Cranking/charging—low-voltage batteries

o Engine—oil leak, tune-ups, and electronic control module failures.
NREL | 47

Propulsion-Related Maintenance Costs by Subsystem: 

Jul.–Dec. 2018 

Maintenance System BEB 35FC BEB 40FC CNG

Mileage 145,281 20,067 235,197

Total Propulsion-Related 

Systems

(Roll-Up of All Systems)

Parts cost ($) 25,439.54 2,204.80 37,496.19

Labor hours 413.0 123.4 376.1

Total cost ($) 46,089.54 8,373.30 56,300.19

Total cost ($) per mile

Without battery changeouts

0.317

0.235

0.417

0.303

0.239

0.219

Exhaust System Repairs

Parts cost ($) 0.00 0.00 13,704.36

Labor hours 0.0 0.0 28.8

Total cost ($) 0.00 0.00 15,142.36

Total cost ($) per mile 0.000 0.000 0.064

Fuel System Repairs

Parts cost ($) 0.00 0.00 1,138.12

Labor hours 0.0 0.0 7.2

Total cost ($) 0.00 0.00 1,499.12

Total cost ($) per mile 0.000 0.000 0.006

Powerplant System Repairs 

(ESS for BEBs)

Parts cost ($) 0.00 0.00 5,581.21

Labor hours 17.4 1.0 173.8

Total cost ($) 869.00 50.00 14,269.71

Total cost ($) per mile 0.006 0.002 0.061

Electric Propulsion System 

Repairs

Parts cost ($) 12,644.00 0.00 0.00

Labor hours 103.6 85.9 0.0

Total cost ($) 17,825.00 4,293.00 0.00

Total cost ($) per mile 0.123 0.214 0.000
NREL | 48

Propulsion-Related Maintenance Costs by Subsystem: 

Jul.–Dec. 2018 

Maintenance System BEB 35FC BEB 40FC CNG

Non-Lighting Electrical System 

Repairs (General Electrical, 

Charging, Cranking, Ignition)

Parts cost ($) 10,518.44 2,174.72 10,196.45

Labor hours 204.4 28.6 95.6

Total cost ($) 20,738.94 3,606.22 14,975.95

Total cost ($) per mile 0.143 0.180 0.064

Air Intake System Repairs

Parts cost ($) 16.53 0.00 1,506.60

Labor hours 0.0 0.0 5.7

Total cost ($) 16.53 0.00 1,791.60

Total cost ($) per mile 0.000 0.000 0.008

Cooling System Repairs

Parts cost ($) 1,563.80 30.08 4,857.21

Labor hours 19.2 7.9 58.4

Total cost ($) 2,523.30 424.08 7,777.71

Total cost ($) per mile 0.017 0.021 0.033

Transmission System Repairs

Parts cost ($) 696.77 0.00 512.24

Labor hours 68.4 0.0 6.6

Total cost ($) 4,116.77 0.00 843.74

Total cost ($) per mile 0.028 0.000 0.004

Hydraulic System Repairs

Parts cost ($) 0.00 0.00 0.00

Labor hours 0.0 0.0 0.0

Total cost ($) 0.00 0.00 0.00

Total cost ($) per mile 0.000 0.000 0.000
NREL | 49

Brake Maintenance Analysis

NREL has been tracking the Foothill Transit BEBs for sufficient time to analyze the differences in brake system costs 

between the BEBs and CNG buses. The duty cycle of the buses can have a significant effect on how components 

wear, including brake system components. The best comparison would be between bus fleets operated in the same 

service. While the bus fleets in this evaluation are operated in very different duty cycles, some general observances 

can be made. The tables below summarize the cost for each bus type. The majority of brake system costs for the 

CNG buses were for relines at 87% of the total costs. Brake relines accounted for only 55% of the total cost for the 

BEBs. The “other” category includes items such as labor for brake inspections and work on parking brakes.

CNG Labor (h) Parts ($) Cost ($/mi) % of total

Reline 131.79 11,883.84 0.0096 87%

Rotor 14.62 293.20 0.0005 5%

Other 20.22 810.31 0.0009 9%

Overall 166.63 12,987.35 0.0110

BEB Labor (h) Parts ($) Cost ($/mi) % of total

Reline 28.12 1,218.71 0.0021 55%

Rotor 0.00 0.00 0.0000 0%

Other 35.38 387.18 0.0017 45%

Overall 63.50 1,605.89 0.0038

• All eight of the CNG buses have had brake relines

• Of the 14 BEBs, 10 have had brake relines

• The majority of relines on the BEBs were front brakes only

• Average distance traveled before the first reline:

o BEB = 92,500 miles (for BEBs that have had relines)

o CNG = 125,700 miles

• Average distance between relines by fleet:

o BEB = 147,700 miles

o CNG = 58,500 miles (rear); 83,900 miles (rear)

• The brake cost for the BEBs is 65% less than that of the 

CNG buses
NREL | 50

Low-Voltage Battery Maintenance Analysis

Foothill Transit continues to have issues with the low-voltage (LV) batteries. The tables summarize the low-voltage battery changeout data 

from the BEB and CNG buses. The BEBs are averaging 7.8 changeouts per bus at approximately 12,000 miles between changeout. The CNG 

buses average 1.13 changeouts per bus at more than 214,000 miles. One issue is that the accessories (farebox, cameras, etc.) continually 

draw power from these batteries. If the master switch is not turned off at the end of operation, the accessories continue to draw power 

from the low-voltage batteries. The CNG buses are equipped with an auto shutoff for the accessories; the BEBs are not.

CNG Bus LV Battery 

Changeouts

Accumulated 

Miles

Miles between 

Changeout

2200 2 230,335 115,168

2201 0 237,749

2202 0 240,518

2203 3 240,174 80,058

2204 2 234,459 117,230

2205 0 248,993

2206 0 250,921

2207 2 248,908 124,454

Total 9 1,932,057 214,673

Per Bus 1.13

BEB LV Battery 

Changeouts

Accumulated 

Miles

Miles between 

Changeout Data Period

2004 5 94,684 18,937 0

2005 6 107,151 17,858 1

2006 6 114,980 19,163 1

2007 5 112,538 22,508 1

2008 8 110,000 13,750 1

2009 8 116,702 14,588 2

2010 5 100,541 20,108 1

2011 8 110,668 13,834 1

2012 7 108,239 15,463 2

2013 7 76,044 10,863 2

2014 8 109,808 13,726 1

2015 19 92,361 4,861 2

2016 9 45,892 5,099 2

2017 8 47,527 5,941 3

Total 109 1,347,134 12,359 20

Per Bus 7.8 1.4

Proterra is aware of the issue and is developing an auto 

shutoff to address the problem. New designs will include this 

feature. Proterra is also working on a retrofit for buses already 

in service.
NREL | 51

Contacts

NREL

Leslie Eudy

Phone: 303-275-4412

Email: leslie.eudy@nrel.gov

Foothill Transit 

Roland Cordero

Phone: 626-931-7246

Email: rcordero@foothilltransit.org

California Air Resources Board

Yachun Chow

Phone: 919-322-7450

Email: yachun.chow@arb.ca.gov

Proterra

Mike Finnern

Phone: 864-214-0393

Email: mfinnern@Proterra.com
NREL | 52

Acronyms and Abbreviations

BEB battery electric bus

Btu British thermal unit

CNG compressed natural gas

dge diesel gallon equivalent

ESS energy storage system

FC fast charge

ft feet

gge gasoline gallon equivalent

GVWR gross vehicle weight rating

hp horsepower

HVAC heating, ventilation, and air 

conditioning

in. inches

kW kilowatts

kWh kilowatt hours

lb pounds

LHV lower heating value

LV low voltage 

MBRC miles between roadcalls

mi miles

mpdge miles per diesel gallon equivalent

mpgge miles per gasoline gallon equivalent

mph miles per hour

NREL National Renewable Energy 

Laboratory

OEM original equipment manufacturer

PM preventive maintenance

PMI preventive maintenance inspection

psi pounds per square inch

PTC Pomona Transit Center

scf standard cubic feet

VMRS Vehicle Maintenance Reporting 

Standards
NREL | 53

Acknowledgments

Produced under direction of the California Air Resources Board by the National Renewable Energy 

Laboratory (NREL) under Work for Others Agreement number FIA-17-1847.
Appendix:

Fleet Summary Statistics
NREL | 55

Fleet Summary Statistics

BEB 35FC 

All Data

BEB 35F 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Number of vehicles 12 12 2 2 8 8

Period used for fuel and oil analysis 4/14–12/18 7/18–12/18 1/17–12/18 7/18–12/18 10/14–12/18 7/18–12/18

Total number of months in period 57 6 24 6 51 6

Fuel and oil analysis base fleet mileage 1,406,520 145,281 29,863 — 1,724,299 187,778

Period used for maintenance analysis 1/15–12/18 7/18–12/18 1/17–12/18 7/18–12/18 10/14–12/18 7/18–12/18

Total number of months in period 48 6 24 6 51 6

Maintenance analysis base fleet mileage 1,253,716 145,281 93,418 20,067 1,932,057 226,981

Availability 86 76 80 75 96 90

Fleet fuel/energy usage in kWh (BEB) or gge (CNG) 3,056,096.9 316,276.0 66,206.3 — 449,421.4 51,774.0

Roadcalls 254 21 14 2 72 18

Total MBRC 5,706 6,918 6,673 10,033 26,834 12,610

Propulsion roadcalls 94 3 4 0 45 14

Propulsion MBRC 15,418 48,427 23,355 — 42,935 16,213

Fleet kWh/mile (BEB) or mpgge (CNG) 2.17 2.18 2.22 — 3.84 3.63

Representative fleet mpg (energy equiv.) 17.32 17.29 16.98 — 4.40 4.16

Energy cost per kWh or CNG cost per gge 0.18 0.20 0.18 0.20 0.97 1.24

Fuel cost per mile 0.45 0.46 0.45 0.46 0.23 0.28

Total scheduled repair cost per mile 0.08 0.09 0.08 0.10 0.12 0.12

Total unscheduled repair cost per mile 0.31 0.69 0.35 0.64 0.14 0.34

Total maintenance cost per mile 0.39 0.78 0.44 0.74 0.26 0.46

Total operating cost per mile 0.84 1.24 0.89 1.20 0.49 0.74
NREL | 56

Maintenance Cost Summary

Maintenance Cost Summary

Propulsion System Maintenance Cost Summary

BEB 35FC

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Total Engine/Fuel-Related Systems (ATA VMRS 27, 30, 31, 32, 33, 41, 42, 43, 44, 45, 46, 65)

Parts cost 82,991.38 25,439.54 7,223.32 2,204.80 137,482.55 37,496.19

Labor hours 1,074.69 413.00 159.56 123.37 1,089.70 376.08

Average labor cost 53,734.50 20,650.00 7,978.00 6,168.50 54,485.00 18,804.00

Total cost (for system) 136,725.88 46,089.54 15,201.32 8,373.30 191,967.55 56,300.19

Total cost (for system) per bus 11,393.82 3,840.80 7,600.66 4,186.65 23,995.94 7,037.52

Total cost (for system) per mile

without low-voltage battery cost

0.109

0.064

0.317

0.235

0.163

0.069

0.417

0.303

0.099

0.095

0.248

0.228

BEB 35FC

All Data

BEB 35FC

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Fleet mileage 1,253,716 145,281 93,418 20,067 1,932,057 226,981

Total parts cost 235,356.89 55,281.61 15,243.47 3,581.50 266,796.55 57,491.65

Total labor hours 5,047.1 1,165.7 509.8 225.7 4,756.2 933.4

Average labor cost (@ $50.00 per hour) 252,356.00 58,285.00 25,490.00 11,286.50 237,809.50 46,672.00

Total maintenance cost 487,712.89 113,566.61 40,733.47 14,868.00 504,606.05 104,163.65

Total maintenance cost per bus 40,642.74 9,463.88 20,366.74 7,434.00 63,075.76 13,020.46

Total maintenance cost per mile

without low-voltage battery cost

0.389

0.344

0.782

0.700

0.436

0.342

0.741

0.627

0.261

0.256

0.459

0.439
NREL | 57

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Exhaust System Repairs (ATA VMRS 43)

Parts cost 0.00 0.00 0.00 0.00 16,155.03 13,704.36

Labor hours 0.0 0.0 0.0 0.0 48.1 28.8

Average labor cost 0.00 0.00 0.00 0.00 2,405.50 1,438.00

Total cost (for system) 0.00 0.00 0.00 0.00 18,560.53 15,142.36

Total cost (for system) per bus 0.00 0.00 0.00 0.00 2,320.07 1,892.80

Total cost (for system) per mile 0.000 0.000 0.000 0.000 0.010 0.067

Fuel System Repairs (ATA VMRS 44)

Parts cost 0.00 0.00 0.00 0.00 3,450.41 1,138.12

Labor hours 0.0 0.0 0.0 0.0 75.6 7.2

Average labor cost 0.00 0.00 0.00 0.00 3,778.50 361.00

Total cost (for system) 0.00 0.00 0.00 0.00 7,228.91 1,499.12

Total cost (for system) per bus 0.00 0.00 0.00 0.00 903.61 187.39

Total cost (for system) per mile 0.000 0.000 0.000 0.000 0.004 0.007

Power Plant (Engine) Repairs (ATA VMRS 45)

Parts cost 1,428.22 0.00 0.00 0.00 51,407.60 5,581.21

Labor hours 48.2 17.4 1.0 1.0 333.4 173.8

Average labor cost 2,411.50 869.00 50.00 50.00 16,670.00 8,688.50

Total cost (for system) 3,839.72 869.00 50.00 50.00 68,077.61 14,269.71

Total cost (for system) per bus 319.98 72.42 25.00 25.00 8,509.70 1,783.71

Total cost (for system) per mile 0.003 0.006 0.001 0.002 0.035 0.063
NREL | 58

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Electric Propulsion Repairs (ATA VMRS 46)

Parts cost 27,921.45 12,644.00 0.00 0.00 0.00 0.00

Labor hours 219.2 103.6 85.9 85.9 0.0 0.0

Average labor cost 10,959.50 5,181.00 4,293.00 4,293.00 0.00 0.00

Total cost (for system) 38,880.95 17,825.00 4,293.00 4,293.00 0.00 0.00

Total cost (for system) per bus 3,240.08 1,485.42 2,146.50 2,146.50 0.00 0.00

Total cost (for system) per mile 0.031 0.123 0.046 0.214 0.000 0.000

Electrical System Repairs (ATA VMRS 30-Electrical General, 31-Charging, 32-Cranking, 33-Ignition)

Parts cost 49,304.34 10,518.44 7,193.24 2,174.72 26,215.75 10,196.45

Labor hours 581.8 204.4 63.8 28.6 321.2 95.6

Average labor cost 29,091.50 10,220.50 3,191.00 1,431.50 16,058.00 4,779.50

Total cost (for system) 78,395.84 20,738.94 10,384.24 3,606.22 42,273.75 14,975.95

Total cost (for system) per bus 6,532.99 1,728.25 5,192.12 1,803.11 5,284.22 1,871.99

Total cost (for system) per mile 0.063 0.143 0.111 0.180 0.022 0.066

Air Intake System Repairs (ATA VMRS 41)

Parts cost 31.80 16.53 0.00 0.00 19,351.95 1,506.60

Labor hours 3.9 0.0 0.0 0.0 7.5 5.7

Average labor cost 195.00 0.00 0.00 0.00 372.50 285.00

Total cost (for system) 226.80 16.53 0.00 0.00 19,724.45 1,791.60

Total cost (for system) per bus 18.90 1.38 0.00 0.00 2,465.56 223.95

Total cost (for system) per mile 0.000 0.000 0.000 0.000 0.010 0.008
NREL | 59

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Cooling System Repairs (ATA VMRS 42)

Parts cost 2,819.80 1,563.80 30.08 30.08 15,592.84 4,857.21

Labor hours 77.2 19.2 8.9 7.9 242.9 58.4

Average labor cost 3,859.50 959.50 444.00 394.00 12,145.50 2,920.50

Total cost (for system) 6,679.30 2,523.30 474.08 424.08 27,738.34 7,777.71

Total cost (for system) per bus 556.61 210.28 237.04 212.04 3,467.29 972.21

Total cost (for system) per mile 0.005 0.017 0.005 0.021 0.014 0.034

Hydraulic System Repairs (ATA VMRS 65)

Parts cost 0.00 0.00 0.00 0.00 0.00 0.00

Labor hours 1.5 0.0 0.0 0.0 0.0 0.0

Average labor cost 75.00 0.00 0.00 0.00 0.00 0.00

Total cost (for system) 75.00 0.00 0.00 0.00 0.00 0.00

Total cost (for system) per bus 6.25 0.00 0.00 0.00 0.00 0.00

Total cost (for system) per mile 0.000 0.000 0.000 0.000 0.000 0.000

General Air System Repairs (ATA VMRS 10)

Parts cost 30,779.14 9,628.90 583.88 185.19 2,384.98 524.39

Labor hours 268.4 70.7 38.8 10.1 47.3 6.0

Average labor cost 13,421.00 3,535.00 1,939.00 504.00 2,367.00 299.50

Total cost (for system) 44,200.14 13,163.90 2,522.88 689.19 4,751.98 823.89

Total cost (for system) per bus 3,683.35 1,096.99 1,261.44 344.60 594.00 102.99

Total cost (for system) per mile 0.035 0.091 0.027 0.034 0.002 0.004
NREL | 60

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Brake System Repairs (ATA VMRS 13)

Parts cost 1,726.41 198.18 0.00 0.00 12,845.95 3,828.26

Labor hours 83.5 25.6 0.5 0.5 170.0 78.0

Average labor cost 4,175.00 1,281.50 25.00 25.00 8,499.00 3,901.50

Total cost (for system) 5,901.41 1,479.68 25.00 25.00 21,344.95 7,729.76

Total cost (for system) per bus 491.78 123.31 12.50 12.50 2,668.12 966.22

Total cost (for system) per mile 0.005 0.010 0.000 0.001 0.011 0.034

Transmission Repairs (ATA VMRS 27)

Parts cost 1,485.77 696.77 0.00 0.00 5,308.97 512.24

Labor hours 142.9 68.4 0.0 0.0 61.1 6.6

Average labor cost 7,142.50 3,420.00 0.00 0.00 3,055.00 331.50

Total cost (for system) 8,628.27 4,116.77 0.00 0.00 8,363.97 843.74

Total cost (for system) per bus 719.02 343.06 0.00 0.00 1,045.50 105.47

Total cost (for system) per mile 0.007 0.028 0.000 0.000 0.004 0.004

Inspections Only—No Parts Replacements (101)

Parts cost 0.00 0.00 0.00 0.00 0.00 0.00

Labor hours 1948.3 267.5 153.2 40.5 2191.6 268.5

Average labor cost 97,414.50 13,374.50 7,662.00 2,026.00 109,580.00 13,426.00

Total cost (for system) 97,414.50 13,374.50 7,662.00 2,026.00 109,580.00 13,426.00

Total cost (for system) per bus 8,117.88 1,114.54 3,831.00 1,013.00 13,697.50 1,678.25

Total cost (for system) per mile 0.078 0.092 0.082 0.101 0.057 0.059
NREL | 61

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC

Data Period

BEB 40FC 

All Data

BEB 40FC

Data Period

CNG 

All Data

CNG 

Data Period

Cab, Body, and Accessories Systems Repairs (ATA VMRS 02-Cab and Sheet Metal, 50-Accessories, 71-Body)

Parts cost 25,014.34 7,553.04 2,030.78 830.70 34,415.88 2,925.09

Labor hours 1077.3 201.5 122.8 34.0 888.3 120.4

Average labor cost 53,865.50 10,074.50 6,142.00 1,700.50 44,412.50 6,018.00

Total cost (for system) 78,879.84 17,627.54 8,172.78 2,531.20 78,828.38 8,943.09

Total cost (for system) per bus 6,573.32 1,468.96 4,086.39 1,265.60 9,853.55 1,117.89

Total cost (for system) per mile 0.063 0.121 0.087 0.126 0.041 0.039

HVAC System Repairs (ATA VMRS 01)

Parts cost 1,360.85 337.06 76.07 0.00 7,962.90 993.18

Labor hours 64.2 20.6 7.0 3.5 81.5 17.3

Average labor cost 3,208.50 1,031.00 352.00 177.00 4,076.50 864.00

Total cost (for system) 4,569.35 1,368.06 428.07 177.00 12,039.40 1,857.18

Total cost (for system) per bus 380.78 114.01 214.04 88.50 1,504.93 232.15

Total cost (for system) per mile 0.004 0.009 0.005 0.009 0.006 0.008

Lighting System Repairs (ATA VMRS 34)

Parts cost 3,304.86 790.13 172.33 172.33 462.55 19.38

Labor hours 161.6 45.3 17.7 13.7 31.8 2.4

Average labor cost 8,079.00 2,266.50 884.50 684.50 1,592.00 119.50

Total cost (for system) 11,383.86 3,056.63 1,056.83 856.83 2,054.55 138.88

Total cost (for system) per bus 948.66 254.72 528.42 428.42 256.82 17.36

Total cost (for system) per mile 0.009 0.021 0.011 0.043 0.001 0.001
NREL | 62

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Frame, Steering, and Suspension Repairs (ATA VMRS 14-Frame, 15-Steering, 16-Suspension)

Parts cost 3,047.82 1,493.14 188.48 188.48 8,354.41 959.17

Labor hours 140.8 69.3 0.0 0.0 80.7 16.6

Average labor cost 7,038.50 3,464.50 1.00 1.00 4,034.50 831.00

Total cost (for system) 10,086.32 4,957.64 189.48 189.48 12,388.91 1,790.17

Total cost (for system) per bus 840.53 413.14 94.74 94.74 1,548.61 223.77

Total cost (for system) per mile 0.008 0.034 0.002 0.009 0.006 0.008

Axle, Wheel, and Drive Shaft Repairs (ATA VMRS 11-Front Axle, 18-Wheels, 22-Rear Axle, 24-Drive Shaft)

Parts cost 1,665.40 0.00 0.00 0.00 21,583.71 1,283.09

Labor hours 13.1 6.1 0.0 0.0 30.8 18.8

Average labor cost 656.50 306.50 0.00 0.00 1,539.50 939.50

Total cost (for system) 2,321.90 306.50 0.00 0.00 23,123.21 2,222.59

Total cost (for system) per bus 193.49 25.54 0.00 0.00 2,890.40 277.82

Total cost (for system) per mile 0.002 0.002 0.000 0.000 0.012 0.010

Tire Repairs (ATA VMRS 17)

Parts cost 79,181.69 9,841.62 4,683.61 0.00 38,602.42 9,462.90

Labor hours 215.3 46.0 10.1 0.0 143.5 29.4

Average labor cost 10,763.00 2,301.00 506.50 0.00 7,173.50 1,469.00

Total cost (for system) 89,944.69 12,142.62 5,190.11 0.00 45,775.92 10,931.90

Total cost (for system) per bus 7,495.39 1,011.89 2,595.06 0.00 5,721.99 1,366.49

Total cost (for system) per mile 0.072 0.084 0.056 0.000 0.024 0.048
NREL | 63

Maintenance Cost by Vehicle System 

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Towing Charges

Charge 6,285.00 0.00 285.00 0.00 2,701.20 0.00

Labor hours 0.00 0.00 0.00 0.00 1.0 0.0

Average labor cost 0.00 0.00 0.00 0.00 50.00 0.00

Total cost (for system) 6,285.00 0.00 285.00 0.00 2,751.20 0.00

Total cost (for system) per bus 523.75 0.00 142.50 0.00 343.90 0.00

Total cost (for system) per mile 0.005 0.000 0.003 0.000 0.001 0.000
NREL | 64

Fleet Summary Statistics: SI Units

BEB 35FC 

All Data

BEB 35FC 

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Number of vehicles 12 12 2 2 8 8

Period used for fuel and oil analysis 4/14–12/18 7/18–12/18 1/17–12/18 7/18–12/18 10/14–12/18 7/18–12/18

Total number of months in period 57 6 24 6 51 6

Fuel and oil analysis base fleet kilometers 2,263,513 233,800 48,059 — 2,774,914 302,191

Period used for maintenance analysis 1/15–12/18 7/18–12/18 1/17–12/18 7/18–12/18 10/14–12/18 7/18–12/18

Total number of months in period 48 6 24 6 51 6

Maintenance analysis base fleet kilometers 2,017,605 233,800 150,338 32,293 3,109,259 365,281

Average monthly kilometers per vehicle 3,513 3,247 3,132 2,691 7,621 7,610

Availability 86 76 80 75 96 90

Fleet fuel/energy usage in kWh (BEB) or gge (CNG) 3,056,096.9 316,276.0 66,206.3 — 1,701,245.1 195,985.9

Roadcalls 254 21 14 2 72 18

Total KBRC 9,183 11,133 10,738 16,147 43,184 20,293

Propulsion roadcalls 94 3 4 0 45 14

Propulsion KBRC 24,813 77,933 37,585 — 69,095 26,091

Representative fleet kg/100 km (energy equiv.) 13.56 13.58 13.83 — 53.50 56.59

Energy cost per kWh or CNG cost per gge 0.18 0.20 0.19 0.20 0.26 0.32

Fuel cost per kilometer 0.28 0.29 0.28 0.29 0.16 0.21

Total scheduled repair cost per km 0.05 0.06 0.05 0.06 0.07 0.07

Total unscheduled repair cost per km 0.19 0.43 0.22 0.40 0.09 0.21

Total maintenance cost per km 0.24 0.49 0.27 0.46 0.16 0.29

Total operating cost per km 0.52 0.77 0.55 0.75 0.32 0.49
NREL | 65

Maintenance Cost Summary: SI Units

BEB 35FC 

All Data

BEB 35FC

Data Period

BEB 40FC 

All Data

BEB 40FC 

Data Period

CNG 

All Data

CNG 

Data Period

Fleet kilometers 2,017,605 233,800 150,338 32,293 3,109,259 365,281

Total parts cost 235,356.89 55,281.61 15,243.47 3,581.50 266,796.55 57,491.65

Total labor hours 5,047.1 1,165.7 509.8 225.7 4,756.2 933.4

Average labor cost (@ $50.00 per hour) 252,356.00 58,285.00 25,490.00 11,286.50 237,809.50 46,672.00

Total maintenance cost 487,712.89 113,566.61 40,733.47 14,868.00 504,606.05 104,163.65

Total maintenance cost per bus 40,642.74 9,463.88 20,366.74 7,434.00 63,075.76 13,020.46

Total maintenance cost per km

without low-voltage battery cost

0.24

0.21

0.49

0.43

0.27

0.21

0.46

0.39

0.16

0.16

0.29

0.27

Maintenance Cost Summary
www.nrel.gov

NREL/PR-5400-72209

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, 

LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the 

California Air Resources Board. The views expressed in the article do not necessarily represent the views of the DOE 

or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, 

acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish 

or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.