CHAPTER 8
Sample Scenarios

The following two sample scenarios provide examples of working through the resilience guidelines for (1) natural disaster evacuations with BEBs and (2) short-term grid outages with a mixed fleet.

Scenario 1: Natural Disaster Evacuation

Step 1: Existing Resilience Plan

The agency knows from its existing resilience plan that its service requirements include providing evacuation services in the event of a natural disaster. These evacuations occur 24 hours per day for a round trip of 50 miles. Usually, the evacuations happen for 72 hours. The threat likelihood is medium.

Likelihood: Medium (Score of 0.3)

Step 2: Incorporate ZE Transition Plan

Based on its ZE transition plan, the agency is planning for a fleet composition of 50% BEBs in 10 years and 100% BEBs in 15 years.

Step 3a: Identify New Threats

Without any mitigations, the 100% BEB fleet will be able to conduct three round trips of the evacuation route before charging is needed. This does not meet the necessary service level. Once the agency reaches more than 50% BEBs in its fleet, it is highly vulnerable to this threat scenario. With less than 50% BEBs, the existing ICEBs are capable of providing evacuation services, so the agency determines that it must start putting in ZE adaptations for this threat before reaching 50% BEB composition in its fleet.

Vulnerability: Highly Vulnerable (Score of 1)

Step 3b: Re-Evaluate Consequences

Without being able to provide evacuation services, there would be severe impacts on public safety and staff. Based on the definitions for consequence severity it defined, the agency categorizes the consequences for a 100% BEB fleet as:

• Customer and Service Impacts: High (Score: 3, Weight: 20%)
• Public Safety Impacts: Very High (Score: 4, Weight: 30%)

• Financial Impacts: Very High (Score: 4, Weight: 5%)
• Equipment Impacts: Medium (Score: 2, Weight: 20%)
• Staffing Impacts: High (Score: 3, Weight: 25%)

Consequences: High (Score of 3.15)

Step 4: Assess Risk

The risk at 100% BEB composition and no mitigations is: High Consequences × Medium Likelihood × Very High Vulnerability = Medium Risk.

(3.14) × (0.3) × (1) = 0.94

Step 5a: Consider Adaptations

The agency determines that there are three potential adaptation measures applicable to mitigating the threat (see Table 14).

Step 5b: Reassess Risk

All of the potential adaptation measures reduce the vulnerability to the threat to medium by allowing the agency to meet its evacuation requirements. Thus, the risk re-evaluated with each of the three potential measures is reduced from Medium to Low.

Medium Likelihood × High Consequences × Medium Vulnerability = Low Risk

Step 6: Evaluate Cost-Benefits and Choose Adaptations

After considering all factors, the agency chooses to prioritize the most cost-effective adaptation, which is retaining a retired ICE fleet.

Step 7: Update Resilience Plan

No action is needed until the fleet reaches 50% BEB composition, which is planned in 10 years. The agency plans to reassess the adaptation options prior to reaching 50% BEB; if there are no changes, the agency will begin retaining retired ICEBs. These steps are added to the resilience plan and long-term capital planning.

Scenario 2: Short-Term Grid Outage

Step 1: Existing Resilience Plan

The agency knows from its existing resilience plan that in the event of a power outage with no compounding disasters, its normal service requirements apply. The likelihood of an 8-hour power outage is high.

Likelihood: High (Score of 0.75)

Step 2: Incorporate ZE Transition Plan

Based on its ZE transition plan, the agency is planning to transition to a mixed fleet with a majority of BEBs and some FCEBs.

Step 3a: Identify New Threats

Without any mitigations, the ZEB fleet would not be able to refuel during the outage. Depending on the SOC or state of fill at the time of the outage, most buses would not be able to complete service. Because of the high utilization of the fleet, the agency has a high vulnerability to the threat after it reaches a 20% ZEB composition in the transition.

Vulnerability: Highly Vulnerable (Score of 1)

Step 3b: Re-Evaluate Consequences

The agency would have to modify or decrease its service until the power resumed and buses could be recharged, so there would be at least one day of service impacts and additional logistics to refuel most of the buses. Based on the definitions for consequence severity it defined, the agency categorizes the consequences for the 100% ZE fleet as:

• Customer and Service Impacts: Medium (Score: 2, Weight: 20%)
• Public Safety Impacts: Medium (Score: 2, Weight: 30%)
• Financial Impacts: High (Score: 3, Weight: 5%)
• Equipment Impacts: Low (Score: 1, Weight: 20%)
• Staffing Impacts: Very High (Score: 4, Weight: 25%)

Consequences: Medium (Score of 2.35)

Step 4: Assess Risk

The risk at 100% ZE composition and no mitigations is: Medium Consequences × High Likelihood × Very High Vulnerability = High Risk.

(2.35) × (0.75) × (1) = 1.76

Step 5a: Consider Adaptations

The agency determines that it has three potential adaptation groupings (see Table 15).

Step 5b: Reassess Risk

The three groups of adaptations reduce the vulnerability by different amounts, with the Large BESS and Large Generator providing the most risk reduction capacity.

Step 6: Evaluate Cost-Benefits and Choose Adaptations

After considering all factors, the agency chooses to prioritize reducing its risk as well as investing in on-site generation that will reduce some of its normal operating costs. It has the space and capital available for a solar photovoltaic (PV) array, a large BESS, and a large ICE generator, so it decides to implement those measures.

Step 7: Update Resilience Plan

Because the fleet is highly vulnerable to outages with as low as 20% ZE fleet composition, the agency plans to begin implementing the adaptations immediately and adds this to their resilience plan and budget.