Efficient maintenance of road networks requires data surface, subsurface and structural conditions. One device for providing structural data on network level is the Traffic Speed Deflectometer (TSD). The TSD measures pavement response at traffic speed, using Doppler lasers installed in a semi-trailer. While providing the user with a large amount of information, indices to evaluate the roads in a simpler manner are needed in practice, e.g., for selecting the worst conditioned roads in a network. In this article, a new index named the \(SCI_{TSD}\) is formally derived from plate bending theory which is proportional to strain in the bottom of the top layer. As opposed to indices such as \(SCI_{300}\) which is developed for stationary instruments, like the Falling Weight Deflectometer, \(SCI_{TSD}\) also works on asymmetric deflection bowls, which are common due to visco-elastic properties of asphalt. Results from comparisons of back-calculated top layer strain on real-life data with \(SCI_{TSD}\) are shown to have high agreement. \(SCI_{TSD}\) is calculated directly on TSD measurements and can therefore be calculated fast. It is therefore highly suitable for helping road authorities select sections of interest and can thereby increase the efficiency of road maintenance.