Mapping Tucson's journey to carbon neutrality

As part of the City of Tucson’s bold adaptation plan, they requested a feasibility study for interim utilization of the Los Reales Landfill gas to power their maintenance vehicle fleet and transit buses operated by Sun Tran, promoting a cleaner, healthier environment, and establishing a circular economy solution.

Our scope involved:

• Conducting a lifecycle assessment of the existing fleet to develop a transition plan and strategy for Tucson’s long term fleet conversion and net zero targets.
• A visual roadmap of a potential closed-loop sustainable system, wherein the City would utilize its landfill gas (LFG) to power the current CNG (Compressed Natural Gas) (compressed natural gas for vehicles) fleet.
• An analysis and recommendation on alternative fuel technologies currently in the market, such as electrification.

Utilizing GHD’s zero emissions vehicle optimization tool, we are providing a fleet assessment for LNG (Liquefied Natural Gas) utilization and electrification, including a summarized study of a zero-emission fleet from a financial, energy and environmental standpoint.

We started by separating the City’s vehicles into two fleet groups for analysis:

• Non-revenue vehicles, including refuse trucks and maintenance vehicles
• Revenue-generating vehicles such as conventional transit buses

Each fleet was broken down further by weight class and assessed at a macro level. Assets are then scored to determine their operational viability in terms of build year, model, make, fuel type (CNG, Diesel), odometer reading, fuel consumption readings, maintenance costs per unit, amortization period, purchase cost, asset expiry date, and service life of the asset.

Vehicle weight class and type summary data is incorporated into the GHD broader techno-economic decision-making model, which includes:

• Transition scenarios showing year over year fleet make-up until the fleet is fully transitioned to ZEVs (Zero Emission Vehicle)
• Financial modelling including the CAPEX and OPEX of operating the baseline fleet and the zero-emission fleet. Over a 20-year period, the OPEX of the fossil fuel fleet rose multiple folds compared to that of the zero-emission fleet. However, as expected, a zero-emission fleet requires a significant upfront CAPEX which would be converted into a reasonable cash flow till 2030
• Utility modelling showing the daily peak demand (KW) for electricity necessary to operate a 100% ZEV Fleet
• Environmental impact modelling wherein the overall GHG emissions are compared for the baseline and zero emission fleets
• Health impact modelling which involved analysis of toxic air pollutants

With the feasibility study still in progress, the assessment data is used to inform the development of a high-level implementation plan for electrification and movement away from the fossil fuel-based fleet.

By utilizing our tools and specialists, we open a window to allow visibility and confidence in the path forward, while removing the risk of the unknown.

The feasibility study is phase one of a multi-phase journey and GHD is happy to be part of the City’s solution to meet their 2030 goals. Our optimization tool will assist the City in preparation of an implementation plan with recommendations to form a long-term strategy.

*The tool is being constantly iterated with new enhancements (subscription model, algorithms, fleet mix) based on demonstrations and positive feedback from leading State of California transportation decarbonization policy makers and regulatory leaders.

Key stats: Based on scenarios run through the tool, once the transition to ZEV’s is complete, projections include:

• $403K savings in operational expenses year over year from lowered maintenance and fuel costs
• 18M Kg reduction of CO2 annually would have otherwise been emitted without transition to ZEVs