This paper presents a new method for signal separation of interleaved pulse trains consisting of several pulse trains emitted from independent signal sources, some of which may only exist for a short time. The separation is based on the differences in the pulse repetition intervals (PRIs) of the signal sources. To detect each pulse train, we derive a map from the input signal to a function of two variables: time and PRI, which we call the PRI map. By taking the absolute value of the PRI map, we obtain a short-time PRI spectrum from which we can use thresholding to estimate the number of signal sources, their time duration, and the PRIs. The PRI map is an extension of PRI transform, which we previously proposed. The extension is based on time-period analysis. The construction of the PRI map resembles a wavelet transform. The difference is that a PRI map is a nonlinear transform, while the wavelet transform is linear. Simulation results are presented on the performance of the signal separation of interleaved pulse trains using the PRI map. Finally, performance analysis shows the detection ability of the PRI map for short pulse trains.