Preparing to succeed: Fleet-wide planning is key in the transition to electric buses
The desire to mitigate climate change and the public health risks of diesel vehicle exhaust are motivating a technology transition in urban bus fleets. In a recent blog, my colleague Yihao Xie discussed targets set by some cities and countries regarding the number or share of electric buses they seek to have in their fleets by a certain year. However, behind the simple numbers, the procurement and deployment of electric buses requires significant effort. My colleague discussed the importance of understanding drive cycles and here I engage with fleet-wide planning.
Because the operation of an electric bus is very different from that of a conventional diesel or compressed natural gas (CNG) bus, transitioning to a fully electric bus fleet requires a rethink of the bus system and consideration of many factors. Without proper fleet-wide planning, this transition would be like building a skyscraper on the fly, without a blueprint and all the measurements and considerations that are part of creating a structurally sound building. Failure in such a transition creates a financial burden for bus operators and the communities they serve, and it can also cause people to lose faith in clean transportation. This would delay the realization of the climate and health benefits of the cleaner technology.
Drive cycle development, mentioned above, is one component of fleet-wide planning, and it helps to simulate the energy consumption of a given route. Along with other components, fleet-wide planning helps determine the kinds of vehicle technology, infrastructure, and operations that will deliver the range and performance equivalent to conventional buses. This is both along individual routes and across the whole network.
Specifically, fleet-wide planning involves a series of steps and analyses that inform estimates of and decisions about such details as optimal battery size, charging strategy, charge-point locations, route distance, route-specific energy usage, battery reserve capacity, expected battery degradation, scheduling, and other factors that shape vehicle performance. For example, accounting for heating and air-conditioning loads and charging speed when selecting battery size helps in purchasing buses with sufficient range. Failure to account for this would result in the need for additional buses or service disruptions. Indeed, testing done in China found that energy consumption increases by 21%–27% when air conditioning and passenger load are at their maximum compared to the minimum. Thus a poor choice of vehicle technology and charging strategy can adversely impact the operational performance of the fleet and lead to higher costs, decreased rider satisfaction, and unexpected changes in fleet capacity.
Detailed analysis of current service, vehicle simulation modeling, and electric bus pilots are all important ways to help with planning and decision-making. ICCT is developing a modeling framework for electric bus deployment that incorporates many of these aspects and can help cities with fleet-wide planning, down to the route-level. Our framework can evaluate and identify appropriate vehicle technology and charging strategy to meet the performance of existing vehicles, and determine the total cost of ownership (TCO), which includes the upfront cost and the operating costs, of the vehicles and infrastructure required to electrify a route. By taking this information and looking across all routes, fleet operators can establish operation schedules, determine financing and procurement needs, and ascertain the required staff training to successfully deliver a fleet-wide transition.
Lessons learned from the early deployment of electric bus fleets in Chinese cities reflect not only the limited range of early generation electric buses, but also the consequences of limited planning. In Shenzhen, Beijing, Wuhan, Qingdao, and Chongqing, it ended up that 1.5–2 battery electric buses (BEB) were needed to provide the same level of service as an existing diesel or CNG bus (i.e., a replacement ratio of 1.5–2:1). For plug-in hybrid electric buses, 1–1.8 units were needed to provide the same level of service as a single conventional bus. China was the forerunner in deploying BEBs, and in those early days, generous subsidies often meant there was little incentive to plan ahead and minimize the replacement ratio. Such high replacement ratios might not be viable nowadays, though, as subsidies are dwindling and government support is typically more limited.
Fleet-wide planning reveals where alternative charging strategies and improvement in operation efficiency can keep replacement ratios and costs to a minimum. One study shows that in China, adequate planning to improve the replacement ratio from 2:1 to 1:1 can reduce the TCO per BEB by CNY1.1 million, down from CNY2.9 million in a worst-case scenario. This worst-case scenario includes a high replacement ratio of 2:1, no subsidy, and high electricity rates over a vehicle lifetime of 8 years. The CNY1.1 million savings alone make the TCO of a BEB less than a diesel bus. The same study found that government subsidies and preferential electricity rates can further save CNY360,000 and CNY170,000, respectively, over the 8-year lifetime.
One fleet-wide planning success story is Metbus in Santiago, Chile. This operator deployed 285 BEBs from 2017 to 2019 and had a replacement ratio with diesel buses of 1:1. Metbus conducted a detailed analysis of its service, and identified a charging strategy and the electric bus specifications such as range and charging speed that would meet its needs. That was key. After 2 million kilometers (km) travelled, the average availability still reaches 99.6%; that means that out of the total inventory, 99.6% of the electric buses are available for use at any given time. The operations and engine maintenance costs for the BEBs are 70% lower than for diesel buses, and due to this success, Metbus is soon increasing its electric fleet to 435 BEBs.
Cities play an important role in leading the transition to zero-emission bus fleets, as they are the major implementors of any state or national policies. Cities can also set their own, higher ambitions. Even when national policies lag behind, success and cooperation among cities can lead to positive change. In addition, major health benefits can be achieved in cities, especially densely populated urban areas.
ICCT’s modeling framework for electric buses, including the models and tools developed, can be applied to different cities for the purposes of fleet-wide planning. However, no two cities are the same. That means that a detailed analysis is needed to understand what each city’s goals and unique challenges are. We’ll be releasing a paper on the modeling we did for Bangalore, India soon, and this will show route-level analysis and results including electric bus range, charging strategy, and TCO. With proper fleet-wide planning, electric buses are a worthwhile environmental and economic investment for cities. They bring cleaner air, reduce greenhouse gas emissions, and are an important part of a more sustainable transportation system.
Sharing advances in best practices regarding research and implementation of soot-free and electric buses is supported by the Climate and Clean Air Coalition’s Heavy-Duty Vehicles Initiative.