Temperature extremes

Reduced range on buses from extreme cold or heat, with high cabin HVAC use, could impact the ability to complete service. Additionally, high temperatures lead to high grid demand events that could shut off power and disrupt charging or refueling.

Batteries need to operate in a narrow temperature range. Driving with or charging cold batteries can decrease battery life (without BTMS). Hot cell temperatures also prematurely age batteries (without BTMS). Some chargers will be inoperable above rated temperatures.

Unexpected range reductions or increased charging times may result in more staff planning or unexpected logistics.

Buses may need to be used as cooling or warming shelters more frequently to protect the public in extreme events. Reduced range during extreme temperatures could impact the ability to complete emergency services.

Reduced fuel economy increases fuel costs. Reduced battery life increases battery replacement costs.

Community trust will be damaged if it is unable to serve in a disaster.

Increased flooding risk from sea level rise and extreme precipitation

Existing routes may become more frequently flooded, requiring changes in service. If existing routes depend on on-route charging or changes to blocks significantly increase mileage, ZEBs may not be able to complete unplanned blocks or routes.

Stationary infrastructure may be at risk for both ICE and ZE fueling or charging stations (U.S. EPA 2020; Raman, Raman, and Peng 2022). While ICE fleets may have to protect a single diesel station from flooding, multiple charging stations around a depot or operating area may be at risk. Additionally, impacts to the electrical grid in other locations may affect energy availability even if an agencyʼs chargers are not affected.

Logistics to move assets or routes out of the flood zone will cause additional stress or potentially put employee safety at risk.

Evacuations may be more frequent or require longer distances traveled to safety. Because hydrogen and charging infrastructure are still developing, refueling away from the agencyʼs infrastructure may be difficult, limiting the range of evacuations. Finally, while hydrogen refills can be accomplished within minutes, charging, depending on the charger infrastructure available, may take much longer.

Some energy assets could be lost due to flooding, if not accounted for up front.

Community trust will be damaged if it is unable to serve in a disaster.

More frequent or extreme natural disasters

More frequent natural disasters could impact electrical service and affect charging and fuel pumps.

Equipment can be damaged from severe weather. Due to charging and refueling infrastructure availability away from the depot, it may be difficult to relocate buses long distances away to avoid damage. On-site energy generation through solar can be decreased by forest fire smoke or snow obstructing panels.

Logistics to move assets or routes to safety will cause additional stress or potentially put employee safety at risk.

Increased need for emergency response, such as evacuations. Range and refueling limitations of ZEBs, as described above, may limit evacuation capabilities.

Damaged equipment may need to be replaced, incurring significant costs to the agency.

Community trust will be damaged if unable to serve in a disaster.

Energy availability: (Hydrogen or electricity) due to hydrogen supply, cost, grid demand reduction events, grid shutdowns or emergency load reductions

Service disruptions in short or long term if charging or refueling not available.

Fuel cells and batteries can degrade if vehicles are grounded for extended periods due to lack of fuel depending on the storage SOC.

Additional logistics and planning can cause stress.

Emergency response capabilities depend on energy availability.

Immature fuel supply chains have fluctuations in cost and availability. Electricity prices are highly variable due to rate structures, which could lead to higher costs.

Impacts to service or emergency response will affect public perception of agency and ZEBs.

Battery thermal events

Depending upon severity, may impact service.

Damage to one or more buses or potentially facilities.

Dangerous for staff. First responders must be aware of situation.

Impacts on public safety if in public.

Replacing equipment or implementing further safety measures may have financial impact.

Safety concerns may impact reputation.

Software compatibility and upgrades: Unexpected software updates to chargers or buses may cause problems with charging or operations

Could disrupt service. Charging disruptions could result in buses not deploying.

Software upgrades could cause incompatibility between equipment.

Unexpected logistics could cause extra stress.

Uncharged buses could not meet service requirements.

Without charge management, high demand charges could be incurred during peak hours, which could result in long-term costs.

Service disruptions damage public perception.

Internet reliability: Charge management or other software may rely on the internet to properly manage charging or other functions

Service could be threatened if buses do not charge on time.

Equipment may not serve its full purpose without connectivity.

Manual charge management requires extra logistics.

Emergency service could be disrupted if buses are not charged on time.

Without charge management, high demand charges could be incurred during peak hours, which could result in long-term costs.

Service disruptions damage public perception.

Security against hacks: Wirelessly connected buses are vulnerable to hacking. ZEBs have additional vulnerabilities through the charging infrastructure. Hackers can disrupt charging protocols or other operations (Sengupta et al. 2023)

Service can be disrupted.

Depending on the nature of the attack, the equipment could be compromised. For example, disabling BTMS or overriding charge current limits could damage batteries or start a fire.

Staff privacy or safety may be vulnerable to hacks if protocols or settings are changed.

May affect public safety or security during the operation of buses, battery thermal events, or a lack of ability to respond to an emergency.

Cyberattacks, depending on severity, can be expensive to contain and recover from.

Public perception could be damaged.

Higher cost of vehicles compared to incumbent technology due to a lack of standardization and individual procurement.

Keeping service affordable is important to customers.

Maintaining equipment may be difficult.

Staff may need to make difficult choices over assets to prioritize.

If higher-cost vehicles result in a smaller fleet, service disruptions could become more common.

Increased cost of replacement parts on more expensive vehicles; higher cost of vehicles initially.

Reputation may be damaged if ZEBs are not deployed.

Equipment compatibility: With rapidly evolving technology, equipment or software such as charger connectors and hydrogen dispensers will change over time and may not have backward compatibility.

Agencies may depend on specific equipment in specific locations (e.g., on-route inductive chargers), which decreases their flexibility and ability to adapt the services provided.

Equipment may become difficult to maintain as technology evolves.

Complicated logistics may result in more staff planning and stress.

Agencies may depend on specific equipment, reducing their ability to borrow equipment in the event of an emergency or refuel vehicles in other locations.

Costly replacements or upgrades may be needed to maintain equipment.

Community trust will be damaged if service is not provided.

OEM instability: Several ZE bus OEMs have had financial difficulties in recent years, causing instability in the market.

Interruption in or lack of support or maintenance for deployed buses can disrupt service.

Equipment may fall into disrepair without preventative or corrective maintenance or parts provided by OEMs.

Additional resources might have to be dedicated to working with OEMs.

Lack of maintenance for deployed buses could limit emergency response.

Agencies could be left stranded with unsupported buses and sunk costs.

Reputation may be damaged if ZEBs are not deployed.

ZE technology requires different knowledge and skills for maintenance and repairs, which existing staff may not have.

Prompt maintenance needed for service.

Equipment may fall into disrepair without preventative or corrective maintenance.

As the ZE transition progresses, staff will increasingly need new skills to remain relevant with new technologies, potentially causing stress.

Proper maintenance needed forsafety of public while traveling.

Lack of staff training could require third-party maintenance, which could be costly.

Poorly maintained equipment could result in decreased service quality, reducing public trust in the agency.