We derive general expressions for the transmission coefficient and the
traversal time in waveguides periodically loaded with dielectric slab
s. We apply the results to resonant tunneling between two regions belo
w cut-off, with exponentially decaying modes. At the resonant frequenc
ies, we found a relationship between the traversal time and the lifeti
me. We also study the photonic band gap in a periodic quarter waveleng
th structure. As in several experiments, we found superluminal velocit
ies.