First I would like to congratulate you on a very fun game.
On with the suggestions. Some of these are repeats....sorry.
Wind. Wind would be a nice addition to the level editing and also adds a new degree of difficulty to game play. For wind you would have two controllable elements, direction and speed. This would be a simple wind, no complex wind simulations like swirling or traps. During normal play the player would not have control over these values. You could expand on it by adding a chance for wind direction or a random value on wind speed. The effect of the wind would be to add a sway to bridge that would cause it to twist breaking more links and eventually collapsing if not built properly.
Cross piece collision detection would be another nice addition, just from a realism stand point. If a cross beam comes down on the road it should bring the road with it if it breaks enough links if it doesn’t then it is a impassable blockage for the train which would be unsuitable if you were a Pontifex.
Train type selection. (Level Editor side) The different trains would have different speeds and different weights, if it’s a freight train vs a amtrack type train.
Ornament. When level editing it would be nice to be able to select from an included set of objects, trees, rocks and whatnot or even user created objects.
Higher resolution ground plane for more depth to the level. A cosmetic bonus. More refined ground plane editing tools would be nice to go along with that as well. Say something like the current tool only with the option to constrain editing to the plane or not.
Someone else mentioned a different gravity or a no gravity situation. A value box with a default of –9.98 for standard earth gravity. But it would be nice for more creative puzzles. 
A nice skydome would be nice cosmetically.
I would happily provide the models and surface maps for all of the above mentioned items. If your are interested feel free to contact me. http://www.nafii.com/neil for representations of my models and other work.
That’s pretty much it for my suggestions
-Neil Nafus
Freelance VFX Artist/TD
http://www.nafii.com
Neil@Nafii.com
ICQ: 2043656
(Edited by GrafxMan at 8:26 pm on July 15, 2002)
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