This work is motivated by the high rate of private car use by commuters in Australian cities. Considering the various benefits of public transport (PT), it is imperative to analyze the shortcomings of the PT networks in comparison to car travel. For this purpose, this work focuses on analyzing the travel time difference between PT and car journeys. This paper presents a methodology to analyze the relative mobility of a PT network in comparison to car travel. The key component of this methodology is the use of two complementary relative mobility metrics that are developed to determine the portions of PT journeys that are inefficient (time-wise) in comparison to car trips. The first metric is the point-to-point relative mobility used to perform spatial distribution analysis, and the second is the PT line relative mobility that evaluates the performance of the PT routes. A demonstration of the methodology is presented by using a case study from Melbourne (Australia). The results of the case study show some inefficient segments of the PT services in several areas, and within the Port Melbourne area in particular. Therefore, this information can be used to assist decision makers to prioritize PT improvements to encourage mode shifts to PT.