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operating regimes are reflected in the sizing of the batteries and as a result the range of the buses, where they vary from 5.9 kWh for the trolleybus design to >300 kWh for overnight charging. This will have a significant impact in terms of the bus’s battery costs; however, the charging infrastructure for overnight charging does not need to be as comprehensive as for the alternative methods. 3.2. Case study: London electric buses London has been working on overnight e-bus demonstrations since 2012 and is also investi- gating the potential of opportunity e-bus technologies. From the overnight e-bus perspective, TfL has collaborated with BYD, which is one of the largest electric bus manufacturer in China, to test the potential of battery electric buses in London, starting from 2012 [45]. The first two battery electric buses were handed over to TfL in 2013 and then entered daily service on two central London routes, numbers 507 and 521, which were the first battery electric buses in London. These single-decker 12-metre BYD buses utilise Lithium-Iron-phosphate batteries and have demonstrated a range in excess of 250 km on a single charge in real world urban driving conditions [46]. The 507 and 521 bus routes are relatively short commuter service routes and were chosen so that the bus can start operating in the morning peak alongside the diesel bus fleet and return to the depot to recharge during the day before resuming service for the evening peak [34, 47]. The battery takes 4–5 hours to recharge when fully discharged and has been designed for a cycle life of more than 4000 cycles, meaning a 10-year battery life- time under normal operating conditions [48]. The trail fleet was extended to six buses in the summer of 2014. The trail buses in London not only provide a zero emission environmental benefit but also have shown promising result in terms of both technical and economic perfor- mance, and hence TfL has taken further steps towards adopting this new clean technology in the capital. The development timeline and future plans for London electric buses are plotted in Figure 7. 0 50 100 150 200 250 300 2010 2012 2014 2016 2018 2020N Development timeline Forecast Figure 7. Number of electric buses in London. Development of Bus Drive Technology towards Zero Emissions: A Review http://dx.doi.org/10.5772/68139 43