Comparing Nonlinear and Threshold Effects of Bus Stop Proximity on Transit Use and Carbon Emissions in Developing Cities

Transit proximity is impactful in providing congestion relief and carbon emissions reduction only within a certain range, while the effective ranges to achieve different policy goals might be distinct. Comparing the impact boundaries of transit proximity on transit use and carbon emissions offers insights for planners to coordinate multidimensional goals more efficiently, but few studies have conducted this comparative analysis. Using 2019 travel data in Zhongshan, this study employed a gradient-boosting decision tree to quantify the nonlinear and threshold effects of bus stop proximity on transit use and commuting-related carbon emissions. Results indicate that the relative impact of bus stop proximity in developing cities is significantly lower than that in developed cities. We found a weaker association between bus stop proximity and carbon emissions than between bus stop proximity and transit use in developing cities. The impact thresholds of bus stop proximity on carbon emissions and the probability of commuting via transit are distinct, and both are lower than China’s current national standards. The findings suggest that some ranges of proximity to bus stops across a developing city can help reduce carbon emissions but cannot help relieve congestion. Most importantly, we found that, due to disparities in the impact boundary on different policy variables and the corresponding analysis criteria, the calculated stop coverage rate varies dramatically. This finding challenges the validity of using national criteria to guide transportation planning and assess land use performance.