There are a number of operational aspects of public transport networks that need to be considered in planning and designing for battery electric bus charging because they can impact scheduling of recharging buses and also the electricity demand requirements.
Urban buses in New Zealand are used in various ways, with weekday usage driven by peak demand, particularly in cities. This is because more buses and drivers are needed during peak periods when commuters and students are travelling compared to the middle of the day and in the evening. An example of this is shown in the graph below which has the number of bus trips by time of day for Wellington City.
Number of bus trips by time of day for Wellington City
The best time to charge a battery electric bus depends on its schedule, with two common scenarios discussed below:
Bus operators may also use battery electric buses for charters (school trips, sports events, etc.) or rail replacement services. Trips that occur outside of public timetables can present challenges, particularly if the additional trips occur when a bus would otherwise be charging. Operators should be aware that non-scheduled trips can have an impact on battery electric bus availability for scheduled public trips.
The costs, benefits, operational considerations, and other guidance related to depot and opportunity charging are provided in:
PTDG: Infrastructure considerations
Guidance related to ranges of battery electric buses is provided in:
A school bus service is a bus route that is operated solely to get students to and from school with members of the general public generally being excluded. The demand for school bus services is highly concentrated between 7:30am and 9:00am and from 3:00pm to 4:30pm because classes tend to start and end at these times. As a result, the number of school bus services will strongly influence the number of buses required to operate a public transport service.
School bus routes can be easier to operate with lower range battery electric buses than public bus services because the distance travelled by school buses per day tends to be short. That said, it is acknowledged that many school routes are combined in or around urban bus service operations.
Another important characteristic of the public transport network is the frequency and capacity required for different types of bus routes as follows:
In general, larger buses require more energy than small buses to travel the same distance due to the vehicle weight. As such, large buses may need opportunity charging or additional battery capacity to achieve the operational range required.
For more information, see:
A layover is the term for the time between scheduled services which is added into a driver’s shift to improve the reliability of the public transport service. This works by providing a buffer between trips so that if the first trip runs late then the second trip can start on time. The amount of time provided for a layover is typically between 2 to 15 minutes. Under the Employment Relations Amendment Act 2018 a bus driver is entitled to 10-minute rest breaks during the workday in addition to a 30-minute meal break. Rest and meal breaks provide drivers with an opportunity to rest, refresh and take care of personal matters.
Full guidance on planning and design for bus layover and driver facilities is available here:
PTDG: Bus layover and driver facilities
From a battery electric bus perspective, layover and driver breaks provide an opportunity to charge a battery electric bus while out of depot. Layovers provide relatively frequent opportunities to charge the bus, however, they are typically short in duration and may be skipped if the incoming bus is behind schedule.
Rest and meal breaks occur less often but have the advantage of being longer in duration and are a legal requirement so cannot be skipped, even if the bus is running late. If opportunity charging during layover is used to top up electric bus batteries, it is important to factor in shorter and skipped layovers where appropriate due to late running. If top up charging is expected during bus layover / driver breaks, this should be factored into choice of battery types as some batteries are more prone to degradation from multiple short burst charges than others, as discussed in the Vehicle range section.
Operational needs for driver or vehicle changeover can affect battery electric bus charging requirements. When a bus driver needs to take a meal break or is ending their shift the bus operator can either:
Driver changeover (also called hot seating) may be preferred by bus operators because it reduces dead running (out of service bus movements). However, a vehicle changeover may be preferred from a battery electric bus charging point of view because it enables the bus to be charged at the depot and may avoid the need for opportunity charging on the route itself.
The travel associated with dead running (which often occurs with vehicle changeover) needs to be accounted for in calculating battery capacity and charging requirements. The degree to which bus operators utilise driver or vehicle changeover depends on the network structure, the location of the depot and any contractual requirements.
Having an interoperable fleet generally results in a more reliable public transport service because it provides more flexibility to the bus operator if a vehicle is out of service for repairs or maintenance.
Meanwhile, a specialist fleet has the advantage of being able to tailor the vehicle to the characteristics of the route such as road constraints, branded livery, and required capacity. Existing diesel bus fleets are typically partly specialised, with most operators having multiple bus sizes and branded buses for special services such as Christchurch’s Orbiter or Auckland’s Northern Express.
Battery electric buses can add another layer of complexity to fleet allocation if various buses of different ranges or charging requirements are used. Therefore, when converting the bus fleet from diesel to electric, public transport contracting authorities should seek to maximise interoperability where possible. This can include charging port locations, compatibility with charging dispensers and chargers, as well as communications and data protocols.
