Semester

Spring

Date of Graduation

2024

Document Type

Thesis

Degree Type

MA

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Scott Wayne

Committee Member

Derek Johnson

Committee Member

Nigel Clark

Committee Member

Hailin Li

Abstract

Abstract

Life Cycle Cost Model for Transit Buses

Connor Jack

Transit agencies battle with reducing emissions while trying to be cost effective. In 2009, the Transit Cooperative Research Program Report (TCRP) 132 presented a life cycle cost model to aid in procurement evaluation [1]. The model is a life cycle cost analysis tool to estimate the overall costs of procurement and compare alternative technologies [2]. The model concentrates on pre-2007 conventional diesel, diesel hybrid with first generation diesel particulate filters, gasoline hybrid, and compressed natural gas transit buses.

The objectives of this work are to implement battery electric technology into the life cycle cost model and update the model to reflect current cost data for all in-service bus technologies. This life cycle cost model evaluates diesel, diesel hybrid, compressed natural gas, and battery electric buses. Data to update vehicle capital costs, maintenance, infrastructure, training, vehicle maintenance, major powertrain component rebuild/replacements, fuel, one-time purchase, and one-time future costs for all propulsion options were collected and implemented. Electric sections were programmed into the model to account for battery electric technology and the complexities of calculating charging costs.

Battery electric buses (BEB) have higher capital costs and charging infrastructure costs than other in-service bus technologies. On average for a 40-foot bus, BEBs cost 38.8% more than a conventional diesel bus, 30% more than compressed natural gas, and 13% more than diesel hybrid options. Utility rates used for charging costs are either time of use or demand rate schedules. The time of use rate schedule is solely based on the draw of kilowatts per hour. Demand rates are comprised of a time of use section with an accompanying demand charge determined by the highest 15-minute energy draw in a billing cycle. Bus charging utilizes on-route or depot chargers, which impact costs for electricity and infrastructure. Based on collected data, the average depot charger adds $88,000 with both charger and infrastructure costs at $44,000 each. On-route chargers are $393,000 with infrastructure costs of $228,000 on average. A benefit to BEB technology is zero tailpipe emissions, but the generation of electricity needed by the buses still produces emissions. Evaluated with default model options, BEBs save $30 million for depot charging and $25 million for on-route charging for fuel costs compared to diesel technology and $3.6 million for on-route and $9 million for depot charging compared to compressed natural gas (CNG). Fuel efficiency for BEB is 17.5 miles per diesel gallon equivalent (mpdge) while diesel is 4.5 mpdge, CNG yields 3.75 mpdge, and diesel hybrids have an efficiency of 5.5 mpdge. All these efficiencies are with minimal to no air conditioning or heating impacts.

A model case study shows that variable costs of BEBs are on average $17.5 million less than all other propulsion types. Variable costs consist of overall vehicle or propulsion only maintenance costs, fuel costs, and any yearly operating grants over the life of the vehicle. The downside to BEB is that capital costs are at least $141 million more than that of diesel buses, around $75 million more than CNG, and $36 million more than diesel hybrid buses. Capital costs consist of purchase price, optional warranty costs, diagnostic equipment for hybrids and BEBs, and spare parts. The main difference between capital and variable costs is that capital costs are the initial one-time costs associated with procurement. Variable costs are associated with recurring expenses throughout the bus’s life. BEBs are less expensive in the long term but the initial costs are higher. Grants and credits may help bring down upfront costs allowing the difference in cost to be more competitive with other propulsion types.

The updates and results of the model provide the ability to evaluate transit buses with current data for evaluation across four different propulsion technologies. BEB is an important option with demand increasing for zero tailpipe emissions. California for example, released legislation that agencies are to be 100% comprised of zero tail pipe emissions technology by 2040 [3]. The drive towards lower emissions gives value to the model being that it has the capability for users to evaluate four different bus technologies and input values for all characteristics evaluated. Additionally, the user could compare multiple scenarios with the same technology type. The complexity of electricity costs makes comparison challenging, output figures and data table provide visual means of comparison.

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