Eight railway stations, P, Q, R, S, T, U, V and W, are connected either by two-way passages or one-way passages. One-way passages are from R to P, T to V, Q to S, U to W, V to R and W to V. Two-way passages are between P and T, V and Q, S and U, and T and U.

In how many different ways can a train travel from R to W without passing through any station more than once?