This chapter shows how elasticity testing of neural networks can greatly aid our understanding of transport systems. It examines several different pieces of work which have the common theme of using neural networks, coupled with a technique of elasticity analysis, in order to reach a better understanding of transport related problems. One of the main reasons for using neural networks is that they can easily represent complex functions, often with nonlinear interactions between different parameters. The chapter focuses on the elasticity of a single parameter with respect to a single network output. However, the elasticity technique can easily be extended to explore mutual interactions between parameters. A three-dimensional elasticity plot is shown of elasticity response against occupancy and speed. When neural networks are coupled with advanced computer visualization tools they provide an immensely powerful tool for general analysis. © V. Himanen, P. Nijkamp, A. Reggiani and J. Raitio 1998. All rights reserved.