CHAPTER 3
Resilience Planning for Zero-Emission Bus Fleets

Resilience Planning

Many agencies have existing resilience plans for their fleets. This section provides a brief overview of general resilience planning concepts applicable to transit agencies, establishing a baseline understanding of resilience that will be used throughout the guide to help agencies update their plans for ZE vehicles.

Resilience is the ability to prepare and plan for, absorb, recover from, and more successfully adapt to adverse events (National Research Council 2012). Through resilience planning, an agency can better manage adverse conditions from unforeseen business disruptions, natural disasters, pandemics, and technology obsolescence that can affect service. Resilience planning requires information gathering about current assets, determining service requirements, assessing adaptation barriers and adaptation measures, formulating plans, monitoring progress, and repeating this process regularly to encompass emerging hazards and unforeseen events.

Threat, consequence, adaptation, and risk are framework concepts used throughout the guide. Threats are any situation or event that can disrupt some aspect of a transit agency; threats are the events that a resilience plan is aiming to address. Threats have both a time duration, geographic distribution, and a probability of occurring. Each agency is exposed to unique threats due to geography, service requirements, and technologies.

Each threat has a quantifiable risk to the agency. In the context of transit systems, risk can be defined as the potential for loss of functionality of a system from exposure to hazards (Transportation Research Board 2021). Risk is quantified as: Risk = Threat Likelihood × Vulnerability × Consequence (Transportation Research Board 2021). The threat likelihood represents how likely it is that the threat will occur. Vulnerability can be understood as the agencyʼs sensitivity to the hazard (Weilant, Strong, and Miller 2019). The severity of the consequence is the impact on the agency as a result of the threat occurring. Consequences can have multiple areas of impact for a transit agency, including:

• Customer and Service impacts: Impacts to ridership, the community, and the regional economy from missed or modified service.
• Staffing impacts: Stress on agency staff due to modifying service, logistics, or other needs from threat response.
• Public safety impacts: Safety of the traveling public during regular service, as well as the agencyʼs ability to fulfill responsibilities during emergency response.
• Financial and operational impacts: Loss of revenue from missed service and operational costs required to modify or adapt service based on available resources and response.
• Equipment damage: Loss of or damage to agency equipment from a hazard.
• Reputational damage: Damage to agency reputation due to threat response, which could impact future funding, ridership, or public trust.

Avoiding these consequences is a key motivation for resilience planning and implementing adaptations. In this guide, an adaptation refers to some measure the agency can take to reduce the risk of a threat.

For further guidance on general resilience planning for transit, agencies can reference:

• FTAʼs Transit Resilience Guide (John A. Volpe National Transportation Systems Center 2024).
• TCRP Web-Only Document 70: Improving the Resilience of Transit Systems Threatened by Natural Disasters, Volume 1: A Guide and the partnering web database of resources (Matherly et al. 2017; Alan M. Voorhees Transportation Center n.d.).
• Risk Analysis and Management for Critical Asset Protection (RAMCAP) Model produced by the American Society of Mechanical Engineers (Brashear and Jones 2010).
• The Federal Emergency Management Agencyʼs (FEMA) guide to Threat and Hazard Identification and Risks Assessments (FEMA 2019, see also FEMA 2020b).

For further information, agencies can refer to the Literature Review in Appendix B or Resilience Planning in Appendix C.

ZEB Transition Planning Overview

Before beginning to update its resilience plan for a ZE fleet, the agency must have a ZE transition plan. The transition plan defines the composition of the fleet and fuel types several years into the future. Without a plan for the technologies, speed of transition, fuel needs, and the level of infrastructure to support the fleet, a crucial component of resilience planning is missing.

A transition plan defines how a fleet will reduce emissions using a few key inputs:

• Service requirements.
• ZE technologies and fuel types that meet the service requirements.
• Size and composition of the fleet.
• The speed of transition desired, or specific goals for emissions reductions.
• Existing infrastructure and available resources for upgrades.

These inputs may vary over the course of the transition period. For example, an agency may plan to transition to fully ZE by 2040. Its total fleet size today may be 100 buses, but in 2035, it plans to have a 120-bus fleet. While the percentage of the fleet that is ZE will change over that time frame, so will the total fleet size, and both are critical for evaluating agency resilience.

Other factors such as cost, regulations, community needs, and service requirements will influence the final plan. At the end of the transition planning process, the agency should have a plan for the composition of its fleet that will meet its service requirements for each period of the transition (example in Figure 1).

This then informs an estimate of how much fuel of each type will be needed throughout each year of the transition, and the infrastructure and investment needed to support that fleet (example in Figure 2).

For more details on transition planning, reference the Guide for Deploying Zero-Emissions Buses or the Zero-Emission Bus Transition Planning Guide (Linscott and Posner 2021, Center for Transportation and the Environment 2024).

Resilience planning for different stages of the transition is important because there will likely be points in the transition where the fleet contains multiple fuel types, each with different resilience strengths and weaknesses. As the fleet composition tips towards a majority or complete ZE technologies, reliance on some incumbent technologies for resilience, such as fossil fuel reserves, internal combustion engine (ICE) contingency fleets, or fossil fuel generators, may decrease. The Antelope Valley Transit Authority case study provides an example of a transit agency that is already past the point of relying on incumbent technology and operating a fully ZEB fleet.