New international transport research has found that relatively small changes in how road space is allocated to buses can deliver outsized benefits for passengers, particularly in congested urban corridors.
The study, published in Transportation Research Part A earlier this year, examines how road space is shared between private cars, buses and bicycles under different demand conditions. Its findings reinforce a long-held position within the bus industry: bus priority only works when it is substantial enough to change behaviour.
The full paper, Roadspace allocation between autos, buses, and bicycles with heterogeneous demand, is available via DOI at https://doi.org/10.1016/j.tra.2026.104884.
Using transport modelling, the researchers found that buses respond to congestion differently from private cars. While car travel times deteriorate rapidly as demand increases, bus performance is more stable because a single vehicle can carry many passengers along the same corridor.
In practical terms, this means buses are better suited to high-demand environments, but only when they are given sufficient priority to avoid being trapped in general traffic.
For Australian and New Zealand cities facing growing populations and constrained road networks, the findings support prioritising buses on busy corridors rather than attempting to accommodate ever-increasing car volumes.
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One of the study’s key findings is the presence of a “threshold” in road space allocation.
The modelling shows that when buses receive too little priority, networks can enter a negative cycle where slower journeys discourage passengers, reducing patronage and weakening the case for investment. However, once bus priority reaches a critical threshold, the system can quickly shift into a positive cycle, with higher usage reinforcing better performance.
In the baseline scenario, that threshold equates to roughly 40 per cent of corridor space being effectively dedicated to buses, depending on how the road is configured. Importantly for planners, the research found that as overall demand increases, the priority required to reach the tipping point can actually decrease.
This suggests that in already congested corridors, relatively modest but continuous bus priority may be enough to significantly improve passenger outcomes.
The research also challenges the idea that buses and bicycles must compete for road space. At higher demand levels, the model shows that the strongest outcomes occur when space is shared between buses and cycling infrastructure, with bus priority becoming increasingly important as passenger volumes rise.
For communities, this points toward integrated corridor designs that support multiple sustainable modes while maintaining reliable bus operations.
The study also accounts for differences in passenger behaviour, including how long people are willing to wait for a bus before choosing another mode. The researchers found that reliability and perceived waiting time play a major role in whether passengers remain on the system, particularly during periods of disruption or change.
This has direct relevance for bus operators and authorities in Australia and New Zealand, where services often cater to a wide mix of school students, older passengers, shift workers and commuters. Consistent, reliable service is not just an operational goal but also a key factor in whether bus-priority investments succeed.
For operators, regulators and planners, the research reinforces several practical lessons:
- Bus priority must be continuous and meaningful to influence passenger behaviour
- High-demand corridors offer the greatest return from bus investment
- Reliability and frequency underpin public confidence in bus services
- Well-designed bus and bike corridors can deliver complementary benefits
While the study is theoretical and does not replace on-the-ground trials, it provides strong evidence that partial or compromised bus priority is unlikely to deliver the outcomes cities expect.
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