| Abstract | Rapid urbanization, increasing transportation demand, and continued motorization have intensified environmental pressures in Bangkok, particularly through traffic congestion and transportation-related carbon emissions. Urban rail transit has been promoted as a low-carbon mobility strategy; however, its contribution to measurable reductions in atmospheric CO₂ concentrations remains insufficiently understood, especially in rapidly urbanizing Southeast Asian cities. This study investigates the relationship between urban rail transit development and atmospheric CO₂ concentration anomalies in Bangkok from 2015 to 2021 using satellite derived XCO₂ observations and grid-based spatial analysis. A 5 km × 5 km grid-based panel dataset was developed by integrating satellite-based CO₂ concentration anomalies, urban rail network characteristics, population, cooling degree days, and wind-displaced external emission sources. The analysis employed a baseline nonlinear regression model, spatial autocorrelation analysis using Moran’s I, spatial model extensions including Spatial Lag-Y, Spatial Lag-X, and Spatial Durbin models, and Monte Carlo simulation-based elasticity analysis. The rail transit variable was constructed using rail network length and rail age to capture both the physical expansion and maturity of the urban rail system. The results indicate that urban rail transit development is generally associated with lower atmospheric CO₂ concentration anomalies in Bangkok. The baseline nonlinear and Spatial Lag X models showed a negative relationship between rail transit development and XCO₂ anomalies, while the Spatial Lag-Y and Spatial Durbin models confirmed the importance of spatial dependence in explaining atmospheric CO₂ patterns. Elasticity analysis further showed that increases in rail transit development were associated with reductions in XCO₂ anomalies, although the magnitude of the effect varied spatially. The strongest negative elasticity was observed in highly urbanized areas, whereas low-intensity zones exhibited weak or near-zero responses. Spillover elasticity analysis under the Spatial Durbin framework revealed that indirect effects were larger than direct effects, suggesting that the environmental benefits of rail transit extend beyond the grid cells where rail infrastructure is physically located. Overall, the findings demonstrate that urban rail transit can contribute to local carbon mitigation in Bangkok, particularly in dense urban areas where travel demand and modal shift potential are high. The study highlights the importance of incorporating spatial dependence, urban intensity, and spillover effects when evaluating the environmental benefits of rail transit development. |
