1. An apparatus for identifying running vehicles using acoustic signatures, comprising: an input sensor configured to capture an acoustic waveform produced by a vehicle source in an area to be monitored and convert the waveform into a digitized electrical signal; and a processing system configured to divide the digitized electrical signal into a plurality of frames; compute at least one spectral feature vector for each frame; integrate said spectral feature vectors over the plurality of frames to produce a spectro-temporal representation of said acoustic waveform, and apply values obtained from said spectro-temporal representation as inputs to a learning function to determine an acoustic signature of the vehicle source.