Hi Glen I had indeed considered the possability of the exact problem you mentioned. I just figured that, as you sugggested, if the timing of the pulses were a problem, an RC circuit coulld be used to "fudge" the circuit into working, one of the reasons I stressed that I hadn't actually built it yet. I'm not enough of a real engeneer to manipulate circuits with the different types of ICs, more of a tinkerer than anything. What's that they say about a little knowledge being a dangerous thing? Last night after I posted the reversing loop diagram I caught a problem that I'd missed earlier. Both sets of sensors, the ones on the loops and the ones on the mainline need to control the turnout positions to ensure that the train goes the right way for the polarity of the loop at any given time. An extra polarity switching relay in series with the turnout switches should solve the problem though. I tried to keep the circuits as simple as possable but sometimes they just won't cooperate. It's still fun to play with though.