Critical path tracing (CPT) is an approximate algorithm used for fast fault simulation, as part of test generation algorithms. It partitions the circuit to be simulated into fanout free regions in order to simplify decisions regarding the propagation of logic signal changes through the circuit. Presented are concepts that result in faster decision making than in CPT for many combinations of input changes. After true value simulation, improved critical path tracing (ICPT) does a more extensive classification of lines than CPT does. This finer classification determines propagation of fault effects without fault simulation in many cases where CPT may require fault simulation. The increase in execution time to incorporate the improvements is insignificant compared to the savings in simulation time for many input vectors. Hence, the extended algorithm is faster than both conventional fault simulation and CPT.