Low frequency guided acoustic waves will propagate many tens of metres along a rail. The guided wave modes that can exist in a rail are found using a 2‐dimensional finite element (FE) technique and their interaction with a variety of features and defects is investigated with 3‐dimensional time‐marching FE models. Results obtained from a prototype testing system are presented and excellent agreement is obtained with FE predictions. Good sensitivity to transverse defects and defects at alumino‐thermic welds is demonstrated. © 2003 American Institute of Physics