  We study random lattice networks consisting of resistor like and diode like
bonds. For investigating the transport properties of these random resistor
diode networks we introduce a field theoretic Hamiltonian amenable to
renormalization group analysis. We focus on the average two-port resistance at
the transition from the nonpercolating to the directed percolating phase and
calculate the corresponding resistance exponent $\phi$ to two-loop order.
Moreover, we determine the backbone dimension $D_B$ of directed percolation
clusters to two-loop order. We obtain a scaling relation for $D_B$ that is in
agreement with well known scaling arguments.
