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Given increasing concern about climate change, the trend toward low-carbon urban transport development has global appeal. The evaluation of low-carbon urban transport is a prerequisite for a transition toward low-carbon urban transport. However, most of the existing research focuses only on the absolute evaluation of urban transport CO2 emissions, which do not represent the level of low-carbon urban transport. In addition, an absolute evaluation is not comparable across different cities over time because it ignores the effects of urban heterogeneity. Therefore, this paper develops a comparative evaluation method that considers the effects of urban population scale, population density and economic development. A benchmark model of per capita CO2 emissions for different cities with different properties is established based on the relationships between urban population scale, population density, and economic development. Then, a comparative evaluation index is derived from the benchmark model to independently evaluate the effects of policy factors, which may reflect the level of low-carbon urban transport. As a result, cities with low-carbon urban transport can be identified. Furthermore, four urban transport transition types are identified: stable high-carbon transitions, stable low-carbon transitions, low-carbon transitions, and high-carbon transitions. These methods are applied to 180 cities worldwide to verify their effectiveness. This is the first time that 180 global cities have been compared using a unified and quantitative evaluation index of low-carbon urban transport.