[en] RADTRAN 4.0 is a computer code for transportation risk assessment developed by Sandia National Laboratories for the US Department of Energy. While retaining the most useful and time-proven features of its predecessors, RADTRAN 4.0 incorporates significant advances over the earlier versions. The most useful new features are: improved route-specific analysis capability, internal radionuclide data library, improved logic for analysis of multiple-radionuclide packages such as spent fuel, separate treatment of gamma and neutron components of Transport Index (TI), and increased number of accident-severity categories. In this paper, each of these features will be described, and, where appropriate, potential applications will be discussed. 11 refs