**1. Introduction**

Electric cars and buses has been proposed by several studies and authorities as a long-term solution for the sustainable development of transport systems, mainly because of their high efficiency, very low emissions when being driven, low noise levels, and the possibility of using renewable sources for their electricity (e.g., [1–3]). Several predictions estimate that electric vehicles will dominate the sales within the next decade (e.g., BloombergNEF believe electric cars will dominate after 2036, and electric buses after 2030 [4] and IEA believe that sales of EVs will be 70% in 2030 [5]) as the price for batteries is likely to decrease and governmental incentives are likely to increase to support such development of the transport sector. A commonality in countries with incentives to tackle climate-change issues related to transport (e.g., taxes on fossil fuels) is that the current approximately 50% higher purchase price for electric cars can be compensated with a much lower price for electricity per km. For example, in Sweden in 2019, the VW e-Golf had a lower total cost of ownership (TCO) after three years (accumulated TCO after five years) than a comparable VW Golf powered by fossil fuels with a mileage of 15 km per year [6]. However, TCO is different for cars and buses, because buses usually have a higher use rate and longer mileage (a bus is normally driven 4–8 times more kilometres than a car). However, bus operators have been reluctant to use electric buses in their operations, mainly because of higher purchase costs and a lack of knowledge regarding how to design, operate, and maintain electric bus systems [7]. Contradictory, a study by Borén [1] summarized several studies about electric buses in Sweden and showed that electric buses can reduce the total cost of ownership for bus operators

by more than 10% over a 10-year period, as well as societal costs due to low life-cycle emissions and noise levels when compared to buses powered by diesel and gas (methane). This depends on country-specific conditions, and a recent study in Texas (USA) show that electric buses can become cost competitive in about 5 years [8], while a study in India show that electric buses can be cost competitive within 25 years [9], and a study in Turkey showed that electric buses have twice as long pay-back time (almost six years) than diesel buses [10]. Since the greenhouse gas emissions from electricity production varies a lot from country to country, electric buses could actually emit more greenhouse gas emissions in total than diesel buses if the electricity used for electric buses is produced with high carbon intensity, e.g., electricity mix in Malta, Poland, Latvia, and Estonia [11]. Some of these emissions can be linked to the production of batteries if there is an extensive use of energy that stem from fossil resources (e.g., oil, coal, and natural gas) [12]. This can, however, be compensated by subscriptions or shares in (or establishment of) new facilities for electricity produced from renewable sources. However, the efforts to reduce climate change and other sustainability impacts cannot only address the transport system, leaving the electricity sector to continue to use fossil fuels. The increase in renewable electricity production and a decline in the cost of it will likely make it possible to achieve a rather quick transition towards sustainable electricity production. Electric buses will then have a minor contribution to climate change and other emissions.

While there can be many environmental and health-related advantages to switch from fossil-fuelled buses to electric, it is important to make that transition relatively easy and cost-efficient to get bus-operators (and taxpayers in the long run) onboard. There have been analyses completed and models/tools designed that focus on charging systems' design and costs [13], location of charging infrastructure [14], costs and sustainability for electric buses [1], life-cycle environmental impacts [12], and procurement processes [15]. There are also several commercial tools (e.g., HASTUS, PtMS, and Optibus [16–18]) used by public transport authorities and bus operators for the calculation of costs related to bus traffic, but without the integration of electric bus systems. Based on that, the authors of this paper have identified a need to focus on modelling and analysis of the total cost of operating electric buses that are charged either at the bus depot or/and along the bus route. What complicates the search for the most cost-effective electric bus system is that the cost of different types of bus systems changes with route properties and timetables.
