Electric School Buses Bring Air Quality Benefits to Utah

A Utah school district is adding clean school buses to its fleet to improve local air quality and mitigate health impacts from bus emissions.

Currently, Salt Lake City School District (SLCSD) is operating 12 electric school buses (ESBs) on longer routes and in diverse four-season conditions. This successful operation demonstrates that ESBs can effectively function across varied elevations and weather conditions, including Utah’s cold winters.

Addressing Air Quality Issues in Utah

Utah has a long history of serious nonattainment status for national ambient air quality standards for particulate matter and increasingly, ozone. Since 2017, Utah has been classified as having higher levels of ozone than the Environmental Protection Agency considers to be safe for public health. The state’s poor air quality has resulted in documented impacts on respiratory illnesses such as asthma, chronic obstructive pulmonary disease (COPD), premature birth, and bronchitis.

SLCSD is situated in the region with some of the worst air quality in Salt Lake County, and the district includes areas that fall within underserved or disadvantaged communities as defined by the U.S. Council on Environmental Quality’s Climate and Economic Justice Screening Tool. Exacerbated health impacts by vehicle emissions, particularly from older diesel buses, underscore the critical need for a transition to clean transportation and prompted SLCSD to explore opportunities for implementing clean school buses.

SLCSD added the first 12 ESBs and one midsize electric vehicle to its fleet in 2020 and plans to introduce 4–6 additional ESBs per year to reach 75 by 2035. The district’s school bus fleet covers 76 routes, typically:

• 40–50 miles per day
• 8–10 stops per route
• Characterized by stop-and-go traffic
• Inclusive of interstate travel for some buses at speeds of 65-70 mph.

ESB Performance and Environmental Adaptability

Utah experiences four distinct seasons with extreme heat and below-freezing temperatures, along with high elevations, steep grades, and road conditions that reflect these challenging weather variations. SLCSD’s ESBs operate in harsh winter conditions such as snow and ice, in addition to temperatures above 90°F as early as May and lasting through September. With a single charge providing a range of up to 100 miles, the ESBs easily accommodate daily demands of 40–50 miles even with heating and cooling demands. In Utah’s dry climate, the ESBs are expected to remain in the fleet for 18–20 years, compared with more humid climates where ESBs have shorter lifecycles.

Based on the fleet's needs, SLCSD Transportation Manager Ken Martinez and his team are confident that ESBs are the right fit for the district.

“We considered natural gas, propane, and electric school buses and felt that the electric school bus option was perfect for our district. In downtown Salt Lake City with the high levels of pollution and traffic, ESBs are a clean means of transporting our students in a city environment,” Martinez said.

Charging Infrastructure

The district began its ESB and charging infrastructure integration trial period in 2020 with four Micro Bird Type A 20-passenger ESBs and four single port JuiceBox chargers using funding from the Volkswagen settlement and grant funding from the Utah Department of Environmental Quality. Since then, SLCSD has installed eight single port Level 2 chargers and four single port DC fast chargers (DCFC), capable of accommodating four new 81-passenger buses and charging a full-size bus in approximately 2.5 hours.

The district also incorporated solar-paneled canopies into its charging infrastructure, which, combined with renewable electricity purchased through Rocky Mountain Power’s Blue Sky program, powers four Level 2 chargers. The combined output of renewable electricity from the grid and solar power has reached the intended 200 kW of renewable electricity. The district also plans to install solar panels on another canopy, aiming to generate an additional 200 kW of renewable electricity to offset the existing chargers. This expansion allows SLCSD to create space for transitioning more buses and other fleet vehicles to electric options.

Driver Training and Considerations

The district is also conducting regular analysis to enhance efficiencies and pinpoint areas for improvement. SLCSD found that their school buses consume the most power while driving on the interstate because the accelerator pedal is used continuously to maintain speed and there aren’t many opportunities for regenerative braking. Once off the freeways, the typical stop and go routes of the school buses allow for use of the regenerative braking system. The district provides driver training on the range variances between city and highway driving, emphasizing factors like speed, merging, and excessive throttle use. The training has been beneficial in creating range confidence and helping drivers plan accordingly for their daily routes.

Moreover, regenerative braking benefits in electric vehicles (EVs) stand in stark contrast to the diesel engine's cooldown process. Regenerative braking in EVs efficiently converts kinetic energy into electrical energy during deceleration, reducing wear on brakes, whereas diesel engines necessitate cooldown periods after high-power operation to prevent overheating and maintain optimal performance. The idling required for cooldown in diesel buses not only contributes to increased emissions, but also poses health risks, especially to children exposed to harmful pollutants emitted during idling periods. By eliminating the need for cooldown, EV buses mitigate these negative consequences.

The district also encourages drivers to operate ESBs for field trips within a 20-mile range as long as the bus has enough charge for its afternoon routes, considering the power demands for running internal heaters and AC throughout the cabin. Trip destinations must be close enough for buses to accommodate a roundtrip without relying on charging during wait periods.

Overcoming Challenges and Costs

The district faced challenges when replacing more than four model year 2001–2004 buses, which emitted the most pollution of the entire fleet, even though they met the requirements for the Diesel Emissions Reduction Act (DERA). The DERA Program requires buses to run at least 7,000 miles every 12 months during the 24 months prior to upgrade, and two of the four buses replaced had well over 14,000 miles traveled per 24 months prior to upgrade, meeting the requirement. However, the other two buses were reserved for emergency use only and thus did not meet the 7,000 mile per year requirement.

With assistance from the Utah Department of Environmental Quality, SLCSD was able to request an exception to the DERA Program requirement to resolve the roadblock for their district and other fleets who may be facing the same problem. The DERA Program makes exceptions for recipients on a case-by-case basis.

The use of ESBs shows promise for the district, and they anticipate the data reflecting this once they analyze cost savings. Martinez highlighted the potential benefits of using ESBs, anticipating significant cost savings.

“The actual moving parts cost a lot less, and we anticipate the hours of overall daily maintenance are going to be substantially less,” Martinez said.

Spreading Success Through Collaboration and Perseverance

Figure 1. Ken Martinez and Tammie Bostick pose for a photo at an event.

Martinez shares SLCSD’s journey, successes, challenges, and future goals to achieve 100% zero-emission buses (including the district’s planned adoption of hydrogen fuel cell technology) with other states and school districts, including the Idaho Association of Pupil Transportation, the Utah Clean Cities Clean Bus and Utility Vehicle Demonstration, and even associations in California and Massachusetts. He also assisted Utah Clean Cities in pushing for Utah’s adoption of clean school bus initiatives, allowing the coalition to promote community awareness and support Utah clean school bus programs. Tammie Bostick, Executive Director of Utah Clean Cities, credits Martinez with driving the clean school bus movement.

"Ken is considered an expert among his school bus fleet peers, extending beyond his own district and state. Moreover, he dedicates his personal time to travel, share, and lead," Bostick said. "He shares his ESB fleet stories nationwide, embodying the necessary leadership of a fleet manager that propels our Clean Cities and Communities partnership one school district at a time. The multiplier effect of fleet-to-fleet camaraderie is alive and well in Utah."

Martinez adds partnerships in facilitating collaboration and sharing of best practices, knowledge, and resources are key to advancing the adoption of ESBs. Through SLCSD’s experience in transitioning to ESBs, Martinez and his team found that successful implementation hinged on public and private partnerships providing equipment, technical support, funding opportunities, and collaboration among other Utah school districts.

Connected by a desire to transition to clean fuels, districts across the state are working together, ensuring that vehicles and the best infrastructure are available for fleet managers to ultimately improve the lives of those living in their community.