This paper discusses the efficiency measure of urban transport operators. We propose a frontier approach, which is compared to the current use of productivity ratios. A survey of the literature leads us to expose our methodology (parametric and stochastic frontier) and to take into account the characteristics of urban transportation in our model. We estimate a production frontier for a sample of 135 urban networks corresponding to years 1995-2002. We analyze the factors which explain inefficiency (for instance the size of networks) and elasticities (return to scale, elasticities of substitution). We show that frontiers improve the quality of efficiency measurements.
