I don't get it.
"Tunnels must start on a single way"? What the heck does that mean ??? I don't think it's married...
You have to draw track up the sloped tile from the lower horizontal tile, in order to be able to draw the tunnel mouth "over" that piece of track.
Ctrl click if you want JUST the mouth (ie not a straight tunnel). Then go into underground mode and use the tunnel tool to build tracks.
If you don't ctrl click, it will cut a tunnel all the way to the natural exit in a straight line. If the exit tile isn't correctly aligned, it won't build.
Yeah, that's what I did.
Ah. Wait. So what if there is already something at the other end?
If you don't use ctrl+click and there's something blocking the other end, no tunnel.
If you use CTRL+click, you also need at least a single empty tile underground in front of the entrance the entrance, otherwise you still get that message.
Gotcha. Seems pretty sick if you are building a road tunnel and at the other end of where the tunnel is there is... a road, but I can live with it.
I believe in that instance, if the road is correctly aligned for the exit (ie same as for an entrance), it will still build the tunnel. If it's wrongly aligned, then it won't.
Once you get going, you'll find building them in underground mode more reliable anyway. Note the tile co-ordinates in the bottom right corner, for calculating where your exit will appear.
How do you make an empty tile in front of the entrance free?
What this means is that you need at least one tile on the underground side. In other words, it might be easier to have said "behind" the entrance.
In pretty much any case you're *likely* to build a tunnel, it will nearly certainly be free. But, for example, if you're building where two slope tiles meet - there's no free underground tile. Like this:
___/\___
But this will work:
____
____/ \____
There's more ways it might work and more ways it might not, but rather than guess: What problems are you having?
Well, just about every time I make a tunnel (and, so far, every time I use ctrl+click, and every time I do a rail tunnel) it comes up with the "Tunnels must start on a single way" message.
Check this out: http://[ simutrans [dot] us (site down, do not visit) ]/isaac/tunnel.jpg
It shows a couple of ways that tunnels will work - the four hills are intended to show two examples, with the road-without-tunnel being a 'before' picture and road-with-tunnel being the 'after'. In both cases, I CTRL+clicked to place the tunnels.
If this doesn't help, could you provide a screenshot of something you're having trouble with?
I don't know if it would help but there's a tutorial about tunnels and undergrounds networks here ;)
=> http://www.simutrans-france.fr.nf/doku.php?id=en:tunnel
http://www.mediafire.com/imageview.php?quickkey=picy51a15taausg&thumb=6
It works on a different computer, but not this one. Will try and reinstall, will tell you whether its worked later.
Also, I feel I should maybe give some computer info -
CPU - AMD Athlon II X4 (64 bit)
GPU - Nvidia GT-210
OS - Ubuntu 10.04 64 bit.
Okay, knowing it works on a different computer means we know you know how to do it, so it's not that. That's good progress. :)
What I would recommend as a next step would be to download another copy of Simutrans and put it in a different directory to test and see if a different *installation* on the problem computer works or no.