Efficient self-organization of informal public transport networks

Human mobility is fundamental to modern societies, and efficient public transport is crucial for sustainable urban development. In the Global North, public transport is typically centrally organized, with fixed routes and schedules. However, this model often struggles to compete with private vehicles in terms of flexibility and ease of use, resulting in lower public transport usage. In contrast, the Global South, encompassing over 80% of the world's population, relies heavily on informal paratransit services, characterized by ad-hoc routes and private operators. These informal systems, primarily using minibuses and vans, are demand-driven and largely self-organized, lacking the centralized planning and significant subsidies seen in the Global North. However, a lack of accessible data has limited understanding of their efficiency and organization. This research addresses this gap by analyzing large-scale data to compare the structural efficiency of formal and informal bus routes globally, aiming to challenge existing paradigms and inform the development of more efficient and equitable public transport solutions.

Existing research on informal transport has largely focused on small-scale case studies or specific regions, limiting broader generalizations about their efficiency. Studies have highlighted the flexibility and demand-responsiveness of informal systems, but also their limitations regarding safety, reliability, and vehicle condition. While some research suggests that competition among informal operators might drive efficiency, a global-scale comparison with formal systems has been lacking. This study builds upon previous research by employing a larger dataset and a more systematic approach to compare structural efficiency across different contexts, providing a broader perspective on the role and potential of informal public transport.

The study analyzes route data from 36 cities across 22 countries, obtained from OpenStreetMap. Routes were categorized as either informal or formal based on operator tags and supplementary information. The data comprises GPS tracks of buses, allowing for detailed analysis of route geometry. To quantify route efficiency, the authors developed a methodology focusing on 'detour profiles.' A route's length is divided into segments, and the detour fraction (the difference between the segment's actual length and the shortest path length between its endpoints, normalized by the shortest path length) is calculated for each segment. This produces a detour profile for each route. Two key observables derived from the detour profile are detour heterogeneity (ξ), which measures the variability of detours along the route, and total detour (D), which represents the overall detour. These metrics are then used to compare the efficiency of routes in cities with informal versus formal public transport systems. The analysis also considers the number of intermediate routes needed to switch between any two routes, as a measure of network interconnectivity. Population density data was used to assess population-weighted efficiency metrics. Statistical analysis, including Mann-Whitney U tests, was conducted to compare the medians of the efficiency metrics between cities with informal and formal transport systems. The robustness of the results was checked against changes in segment lengths used in the analysis.

The analysis of over 7000 bus routes revealed that informal transport networks often self-organize with surprisingly high efficiency. Cities with informal public transport systems consistently exhibited lower detour heterogeneity (ξ) and total detour (D) compared to cities with formal systems. This means that routes in informal systems tend to be straighter and have fewer detours overall. The median detour heterogeneity for informal systems was 0.011, significantly lower than the 0.070 median for formal systems (p-value = 0.0007). Similarly, the median total detour was 0.12 for informal systems and 0.45 for formal systems (p-value = 0.00005). These differences were statistically significant, strongly suggesting that the observed differences are not random. Interestingly, the number of intermediate routes required to connect two routes was comparable between informal and formal systems, indicating similar levels of network connectivity. These findings hold even when accounting for population density, supporting the conclusion that informal systems achieve high structural efficiency without the substantial subsidies common in formal systems. The results remain robust across various methodological variations.

The findings challenge the conventional view of informal public transport as inferior and highlight its potential for efficiency. The lower detour and heterogeneity observed in informal systems might be attributed to dynamic interactions between drivers and passengers, where competition for customers drives efficiency. While the study focuses on spatial aspects of route efficiency, further research is needed to investigate temporal factors like waiting times and service reliability, which also contribute to overall service quality. The inherent profitability of informal systems, necessary for operator livelihood, contrasts with the often subsidized formal systems. This study's global comparison offers a valuable perspective on the efficiency of self-organized systems, which could inspire innovations in public transport design and planning.

This study demonstrates that informal public transport networks in the Global South often self-organize with high structural efficiency, outperforming formal systems in the Global North. The lower detour, more uniform paths, and comparable connectivity in informal systems suggest that self-organization can be a powerful mechanism for creating efficient public transport. Future research should incorporate temporal data to assess overall service quality and examine the interplay between self-organization, regulation, and sustainability. The findings challenge existing transport planning paradigms and suggest potential for more equitable and sustainable public transport solutions globally.

The study primarily focuses on spatial aspects of route efficiency, using large-scale microscopic data on route geometry. Temporal information such as waiting times, service reliability, and frequency of trips was limited, potentially impacting the overall assessment of service quality. Furthermore, the data used relies on OpenStreetMap, whose completeness and accuracy may vary across cities and regions. Future research incorporating more comprehensive data, especially temporal aspects, would provide a more holistic understanding of informal transport system efficiency.