Multi-objective Routing Optimisation of Walking School Buses for Health and Environmental Sustainability

Walking school buses (WSBs) provide an alternative mode of transport for children to commute between their home and their school. In this mode ‘bus drivers’ (parents) pick up ‘passengers’ (children) and walk to school together. WSBs have many advantages over conventional modes of transport for the school commute, in particular, parents driving their children to school individually.
• Active travel to school can increase children’s concentration in learning by up to four hours (Sustrans, 2016).
• Children benefit from the contribution the exercise provides towards their daily exercise target and the practical experience with respect to road safety.
• Modal shifts from cars to WSBs might help relieve traffic congestion around the entrance to schools.
• WSBs do not contribute to air pollution.
For these reasons, the feasibility of WSBs is investigated in many places, see for example (Neuwelt and Kearns, 2006) for a study in Auckland, New Zealand.

However, the design of WSB routes is far from trivial. Assuming the starting point of a WSB route to be known, the basic version of the problem is to find an optimal route to the school and children will be picked up along the way. Here, optimality of a route does of course relate to travel time. However, it must also take into account air-pollution exposure along the route: A recent study in Bradford has shown that walking on different sides of the road, depending on the traffic level and traffic management arrangement, could make a significant difference to the contribution of air pollution dose during journey to school (Dirks et al., 2016). Naturally, the WSB route can avoid busy roads with high levels of air pollution by walking longer, greener routes. However, this is at the expense of travel time, and probably reduces the number of children that can share the ride on WSB hence is impractical. For this basic form of the problem, bi-objective shortest path methods, like the one for cyclist route choice described in Ehrgott et al. (2012) can be adapted.

In reality, the starting point of the WSB route is also part of its design as well as the intermediate ‘bus stops’. Thus, adding an additional level of complexity, the problem now becomes more like a vehicle routing problem. A number of WSBs are allocated routes to pick-up passengers on the way and rather than starting from a common ‘depot’ to which the vehicles (here the bus drivers, i.e. parents) return, these routes start at several vehicle locations and end at a common destination. Again, this vehicle routing problem will consider the conflicting objectives of travel time and air pollution exposure. The order of picking passengers is now also part of the design.

An alternative design of a WSB would consider a model where children are picked up not at their home, but at agreed meeting points. Parents would walk their children to these ‘bus stops’, where they join the WSB as passengers. Therefore, this version of the problem includes the stop location problem as part of the design. Now the literature on public transport planning where issues of route design and stop location optimisation are discussed becomes relevant, see e.g. Kroon et al. (2016).

The aims of this project are to review the literature on WSB and derive optimisation models for the various versions of the problem in an incremental manner. With reference to current literature on shortest path, vehicle routing, public transport and multi-objective optimisation, effective and efficient solution algorithms need to be developed. In addition to building the theoretical foundation of this meaningful optimisation problem, this project will offer an opportunity to work with two schools in the Bradford area on practical issues of the implementation of WSBs to maximise the impact of this research.

How to Apply: You must submit an online PhD application by the deadline. Details of how to apply are here: http://www.its.leeds.ac.uk/courses/phd/apply/. You must clearly state the project name in the project details. You should include a ‘statement of motivation’, which should be 1-2 pages and should state why you feel you are well suited to the topic. This may refer to your academic background and any relevant experience and could include an indication of how you would choose to interpret the project. Enquiries about the application process can be sent to Deborah Goddard ([Email Address Removed])

Informal enquiries can be sent to Dr Judith Wang ([Email Address Removed])