well, easiest way would be to change them for better rails.
or you could try to use the kind of iron-wool pads from the kitchen (for scrubbing pots and pans)
but be carefull. Bachmann rails are hollow. very weak and thin material.
You may already know, but Bachmann track is not made for exterior applications, and will not realistically last that long indoors, either. If you are running battery power, you might make it a while longer by using Kormsen's advice.
If you are using battery you could spray the rails with one of the "rust reformers"--can get them at the auto parts store. Turns rust to a black paintable surface--then paint the rails with a primer. Might make them last outdoors longer as well.
If you have track power I would use 1200 grit sandpaper lightly to "polish the rust off the rail head.
To quote TOC (The Old Curmudgeon aka Dave Goodson, Guru), "Cut and throw".
Bachman track is disposable junk made for around the christmas tree maybe one or two years that seems to have been the life of the 1st gen sets.
Buy some decent solid brass, aluminium or stainless steel track and forget the rust.
Bachman have improved the drive many times so they now go for years but the track stays the same, not going to encourage newbies if you've got a train and now want to expand but no track any-more, a marketing screw-up if you ask me.
I remove rust off my bachmann track with a product called RUST AID from walmart 9.00 a gallon it works great. I removed rust from a lot of bachmann track. WIPE ON AND RUB OFF AFTER DRY. I then paint the track where the rust was but only polish the upper part of the rail where it makes contact with wheels turtle wax rubbing compond works great after rust is removed be sure to clean off track with water after you use it or it will put crud on your engine wheels
The use of steel wool pads should be avoided. The pads will leave behind small bits of iron shavings. Electricl motors contain magnets which will tend to attract the iron shavings. There is a risk of the iron shavings building up to the point of causing a short circuit in the electrical path from track to motor.
I agree with others, replace the Bachmann track with a more durable variety, be it brass, aluminum, or stainless steel.
I know several people with fairly large indoor layouts in their dry basements who use Bachmann steel track exclusively. One guy (bachelor of course)has it running through out the main floor of his home.They love it because it is cheap, and can be bought at giveaway prices on Ebay.
Bachmann switches seem to be very reliable as well. There is enough variety of product to make up some complex track arrangements.
Not everyuone can afford the more expensive track, like most of the members who responded above. I would rather see someone in the hobby with Bachmann track than sitting around in the old armchair. So if you have a dry area indoors, and want to use Bachmann track products just go for it.
I agree, Bachmann track can be used indoors. It can also be mated with LGB-type track as well. Simply take the Bachmann track and wiggle out the black metal tongue from the track. Try not to bend up the rail. Then it is a simple matter to squeeze the end of the Bachmann track a bit and slide it into an LGB-type connector.
I have used this method to mate the two type of track together. Save the black metal tongue from the Bachmann track in case you want to go back, simply slip it back into the open end of the Bachmann track. I have not tried this method with Hillman or Split Jaw-type clamps but if not tightened too much it should be possible to mate Bachmann to LGB with a rail clamp.