We calculate numerically the transmission coefficient and the traversa
l time for finite Gaussian wavepackets as a function of their widths.
We consider electromagnetic waves crossing a slab and a periodic struc
ture. We find that the periodic structure can be crossed at superlumin
al velocities for wavenumbers in the optical gap and sizes larger than
the thickness of the system. The corresponding transmission coefficie
nts are very small. The long wavepacket limit of the traversal time co
incides with previous analytical results for the real component of the
interaction time. The imaginary component of this time only affects t
he change in size of the wavepacket.