I used to remember Transport Tycoon by Chris Sawyer, this was a brilliant game, a bit outdated now and probably won't work on most newer systems, but I do know there was a follow up called Transport Giant...
For the Open Transport Tycoon website, visit here...
http://www.openttd.org/en/
For the Transport Giant website, visit here...
http://www.transportgiant.com/
As mentioned above there is also Railworks, which was made in the UK, the website link is here...
http://www.railsimulator.com/ but be warned that for any add-on content, you will have to pay for, also I found the surveyor or
editor as they call it, part of the program is very fiddly and can be very frustrating (I recommend a swear box to be set up, before going into Editor, to raise money for your local charity, you should easily make $10 in five minutes).:hehe:.
For me, I save the best till last, and I will gladly recomend Trainz 2010 to anyone, you get tons of well made content for free on the download station made by our superb creators, you get the most friendliest forum family around, and an easy to use surveyor in Trainz 2010, were you can build a route in 5 minutes and not a swear word being heard, (unfortunatly your charity misses out).:'(. For Trainz 2010, The best in the business, visit this link...
http://www.ts2010.com/
Hope this helps
Joe Airtime