Enhanced bus networks
Improving a bus network’s layout and timetables can mitigate carbon emissions in several ways. It can:
- Attract riders from more polluting modes, namely cars.
- Reduce the need for the construction of transport infrastructure.
- Minimise bus fleet requirements.
- Eliminate inefficient bus operations.
Planners can apply various established algorithms and heuristics to identify network designs that improve operations while balancing user and operator costs. To also minimise carbon emissions, planners should ideally:
- Account for the external costs of carbon emissions in operator costs.
- Account for emissions from infrastructure construction and fleet procurement.
- Consider hierarchical route structures (i.e. trunk and feeder lines) and skip-stop services (i.e. services where some stops are skipped, e.g. to enhance the reliability of the services and shorted travel times).
- Allow for variation in station spacing.
- Adapt vehicle sizes to passenger demand and switch to low- (or zero-) carbon emission vehicles.
- Consider comfort and convenience features beyond travel time improvements that attract ridership.
- Account for uncertainties in demand patterns when developing demand forecasts.
- Facilitate inter-modality and (physical) accessibility to public transport, especially by creating multi-modal transport hubs that encourage the use of active modes (cycling and walking) or other means of public transport.
Multi-modal hubs will encourage the use of sustainable modes to access bus services - and for the onward journey - and can help increase bus ridership. Measures can include (please refer to the respective measure descriptions available on TCAD):
- The provision of respective infrastructure, such as cycling lanes to/from bus stations or stops, as well as secure and easily accessible bicycle or shared vehicle parking facilities.
- The integration of the bus system with public (shared) vehicle schemes and other public transport services by integrated ticketing, or ideally, comprehensive Mobility as a Service (MaaS) solutions.
Existing assessments of bus projects offer critical lessons for agencies to anticipate and overcome practical and political challenges when planning for new and/or enhanced bus services:
- Consult with users and stakeholders.
- Retain route planning under public authority.
- Provide a dedicated planning team with the data and resources.
- Involve high-level decision makers to foster collaboration between agencies.
- Plan for expansion, prepare contingency plans and adapt services to revealed demand.
- Design operator contracts to enhance competition, align incentives with major performance metrics and avoid renegotiations that tend to favour operator profits.
- Separate ownership of assets from operating concessions to facilitate competitive tendering and investment in clean technologies.
Enhancing bus networks can reduce emissions thanks to an increasing mode share of public transit and reduced transport activity on less efficient modes. They can also increase the energy efficiency of the bus network itself. Savings will depend on the size of the city, the efficiency of the current system and the degree of the bus network improvements that are being implemented. The following estimates of the potential impact of bus network enhancements on carbon emissions can, among others, be identified in the available literature. They show that carbon emissions reductions from bus networks can often be substantial thanks to network improvements.
- In Dalian, China, implementing optimal skip-stop services can reduce emissions of the bus network by 13% (Tang, 2018).
- In Barcelona, Spain, adjusting the network structure, routes and timetables could reduce carbon emissions by up to 50% with no significant change in user costs or average travel times (Griswold, 2017).
- In San Francisco, United States, optimising the MUNI system would cut carbon emissions by two thirds (Madanat, 2016).
- In Madrid, Spain, optimising vehicle assignment would reduce carbon emissions by 6.5% and NOx emissions by 2% (Jiménez, 2016).
- In Baoji, China, optimising a system of 38 routes could reduce carbon emissions by 4% (Sun, 2013).
Since fuel consumption accounts for a significant portion of operator costs, network configurations that minimise carbon emissions typically, but not always, also reduce operator expenses.
- In Beijing, China, an optimised feeder bus line reduced peak-hour operating costs by 31-64% (Zhang, 2020).
- In Dalian, China, implementing optimal skip-stop services can reduce fleet size by 12.5% (Tang, 2018).
- In Shanghai, China, minimising carbon emissions from passenger transport would increase operator costs and crowding (Zhang, 2017).
- In Barcelona, Spain, adjusting routes and timetables could reduce operator costs by 17% (Griswold, 2017).
- In San Francisco, United States, optimising the MUNI system would cut costs by 50% (Madanat, 2016).
- In Baoji, China, optimising user and operator costs alongside carbon emissions would increase revenues by 5% (Sun, 2013).
For systems with sub-optimal networks or a high likelihood of diverting drivers to public transport, enhancements that reduce net carbon emissions may also lower travel times.
- In Beijing, China, an optimised feeder bus line reduced peak-hour wait times by 54-70% (Zhang, 2020).
- In Baoji, China, optimising a system of 38 routes would cut average travel times by 5 minutes (Sun, 2013).
Public transport systems contribute to negative externalities beyond climate change, such as local air pollution, and positive externalities, like providing access for those who cannot drive. Failure to account for other externalities when redesigning a bus network could result in adverse effects.
Optimising routes and frequencies to reduce carbon emissions may entail service cuts in low-demand areas, which could have severe adverse effects on accessibility and social equity. For example, this was an issue with the major reform of bus services in Santiago de Chile in 2007, with job losses following increased travel times on some routes. The reform focused on cutting operating costs by introducing a hub and spoke system to concentrate passenger flows, regardless of end-to-end travel times. Subsequent reforms with broader objectives have resolved the issue.
Bus rapid transit (BRT) networks couple all the enhanced bus system features discussed here with physical infrastructure to increase capacity and improve operations. BRT systems can, however, be somewhat less flexible than traditional bus systems and require substantial street space for dedicated lanes and stations.
Measures that encourage the use of bus services via better integration and enhanced accessibility of the bus network can increase bus ridership. Examples include creating multi-modal hubs or public transport stops via respective infrastructure and service provision (e.g. easy access to shared vehicle systems or other public transport modes) or digital solutions (e.g. integrated ticketing, Mobility as a Service).
ITF (2021) Transport Climate Action Directory – Enhanced bus networks
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