Complex network theory describes network performance mostly based on topological characteristics, like betweenness centrality. This work integrates concepts from complex networks and traffic engineering. We propose a new measure for spatial networks and, in particular, for multimodal transportation systems. We give the definition of dynamical efficiency for single- and multi-layer networks. This measure is based on the concept of " reachability " of a location in the city according to the road traffic and to the available modal choice. The dynamical efficiency captures the topological changes in a multilayer network due to the congestion like the average loss in travel time from and to each link and the centrality of intermodal stations. Moreover, we show a method to calculate for each interchange station the so-called dilemma factor, that is a measure of substitutability of the best path choice with an alternative way in an integrated complex variegate transportation system. There are several advantages in using this measure for analyzing a multimodal urban mobility both on the side of the complex network theory and on the practical engineering applications and we briefly illustrated some of them in the conclusion. A detailed application on a megacity has been carried out on a real network with probe traffic data.