How does parking availability interplay with the land use and affect traffic congestion in urban areas? The case study of Xi'an, China

Strategic development of parking spaces is considered as one of the leading solutions to alleviate urban congestion. However, few studies have quantified the interactions between land use and parking to investigate their emission impacts on traffic congestion. This study introduced a novel dimensionless ratio, the Extra Carbon Emission Index (ECEI) which estimates carbon dioxide (CO2) increments in the congestion condition of free-flowing traffic. Using a publicly accessible web-mapping service application, we collected the traffic speed data from dynamic urban road networks during peak hours of Xi'an city, China in 2017. A multiple regression model was applied to analyse the tripartite relationship among land use, parking availability and the ECEI. The results suggest that 1) supply-demand ratio of parking spaces, density and land use mix are negatively correlated to congestion; 2) parking availability is positively associated with spatial-temporal distribution of traffic flows, and this land use differentiates congestion in time and throughout the built environment; and 3) low-density parking lots and high-density parking spaces increase traffic congestion in residential districts, while adversely affect the compact land use towards sustainability. Compared to the reconstruction of land use, parking reform provides a more efficient way to alleviate congestion by coordinating the density of lots and spaces in residential districts.