Tunnel clearance...What a headache. I've already submitted an article about clearance in general, but the topic in this hobby is endless. Someone recently mentioned tunnels and I've been having nightmares about them ever since. It seems you always hear about someone having to delay a session because the cat's asleep or won't budge out of the tunnel. Then there's the gross-out stories over the years about dead mice turning up inside tunnels, moist corpses shorting the line, nesting in the mountian, etc. One aquaintance in Las Vegas had to rip out and replace a line from rodent urine. Good clearance is best achieved by the most open access possible. Beyond the elimination of newspaper following a modelling project, tunnel access is as important for you as it is for the people who build the real ones. I've mentioned before and don't have to tell half of you about "The Aging Human Body Vs. The Layout". I first heard "Don't go any deeper than your arm can reach" actually in reference to MRR tunnel construction. I adapted this novel concept to diorama depth as my back went to oatmeal! It's still a good idea for tunnels too, but why? Instead of asking yourself; "Why am I making a tunnel?", you should ask yourself "Where can I USE a tunnel?" Tunnels are a lot of work to build and maintain. Beyond selecting and labouriously painting a portal, there's the interior to perfect as well. After the terrain above is to your satisfaction, comes the hard part, the maintenance for the service life of the tunnel. Most people shy away from situating a tunnel in the middle of a layout unless they're recreating the Fraser River Canyon or the Arlberg Pass. Why? It deprives too much valuable space from structures, industry and yards. We usually situate them on a corner of a layout to hide a sharper curve than was desired, curving around a backdrop, or leading through a backdrop separating a drastic change of setting. Corner tunnels are the best. To the viewer, a train goes straight in, and comes straight out. This is easier on the eye than constantly watching trains snaking around too many curves. I've noticed over the years that less curves and realistic speeds tend to make viewers more relaxed. I think it also makes the layout look larger. Island layouts are a charm for making access panels on blunt, undetailed corners where a curve is hidden underneath. Even a dark cloth tacked to the wooden framework is fine for concealing trains on sharp curves yet allowing access for cleaning, and those occasional pesky derailments. DCC is fantastic until you have your first rear-ender in a tunnel! Island layouts also provide access points for tunnels from the inside controlers area where spectators cannot see. Just keep the access area covered when not in use so when the curious eyeball peers down the tunnel, all they see is darkness. For around the wall type layouts, making a sleeve frame for the tunnel portal as described in a previous article is best, and then again, don't make the tunnel mid-point deeper than you can reach from either end. It was once said that; "Man's reach should always exceed his grasp". I guess so when there's a train off the tracks in a tunnel! Happy Rails! George.