Evaluation of In-Use Fuel
Economy for Hybrid
Transit Buses
Shauna Hallmark, Bo Wang, and Bob Sperry 2012 Mid-­Continent Transportation Research Forum September 6, 2012 1
Background
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Fuel costs are significant portion of transit
agency budgets
Hybrid technology offers attractive option
•  Upfront costs are significant
•  $280,000 to $300,000 vs. $550,000
•  In-use fuel economy not well documented
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Background
most are laboratory studies
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Motivation for Study
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$250,000 budget deficits for CyRide,
motivated to reduce fuel costs
12 hybrid buses purchased
through TIGGER Grant
Needed to justify
investment
Little information on
in-use fuel economy
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Study Background
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CyRide: city bus system for Ames, IA
and Iowa State University
Around 4.3 million passengers per year
CyRide has 12
fixed routes with
buses rotated off
and on routes
2% biodiesel
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Methodology
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12 hybrid buses
• 
“Cybrid”
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Methodology
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12 hybrid buses
7 regular buses had similar
characteristics
•  Selected as controls
•  But data for all buses were recorded
Assumed buses were equally likely to
be assigned to a particular route/driver
combination
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Methodology
CyRide Bus System
Recorded Variables
•  Trip
•  Ridership
•  Amount of fuel added
•  Mileage
•  Fuel Type
•  Maintenance Information
•  Trip Code Reference
CyRide Transit System
in Fall 2011
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Methodology
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Data collection began July
2011
Several adjustments made
to hybrid buses over study
•  Replace or adjust brake
pedals – affects
regenerative energy
•  Software adjustments to
smooth bus shifting
patterns
•  Air condition/heater
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Methodology
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Fuel Economy Analysis Results
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Summary
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Average hybrid bus fuel economy: 4.8
Average control bus fuel economy: 4.2
Overall fuel economy for hybrid buses 12.1%
higher than regular buses
Other on-road studies
•  Toronto Transit Corporation – 10%
•  FTA – 5 to 18%
Preliminary results, will complete with 12
months of data
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Long-Term Costs
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Benefits
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Approximately 12.1% better fuel economy
Reduced engine wear
•  50 to 100% improvement in brake life for hybrid transit
buses (Transport Canada)
Costs
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• 
Replacement of battery pack
•  Potentially at 5 to 7 years
•  Costs is uncertain because future battery technology is
somewhat unknown
Additional weight may increase wear on shock absorbers
and tires
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Study Limitations
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Changes were made to the hybrids over time
Assumed study vehicles were equally likely to be
assigned to route/driver, impacts
•  Driving style
•  Route
•  Number of starts and stops
•  Loading
•  Above factors are being included in final analysis
Extremely mild winter (2011/2012) not representative
of normal winter conditions
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