Acceptable grades

[MountainMan]

Most people seem to run 1.5% to 2.0% for convenience sake, given the length of track necessary to get decent separation; however, model locos will handle grades up to around 4% with a little fine tuning, proper balancing and weighting, and a liberal dose of Bullfrog Snot. Prototype railroads did a lot more than that. The Florence and Cripple Creek Railroad climbed 5,000 feet in around fourteen miles, at an average grade of 4% and a final grade of 6% at the Wilbur Loop. Logging railroads have been known to operate at up to 9% grades. Another trick is to place a small motor from a switching diesel or the like into a tender and use it to supplement the power of your engine.

If you haven't got room for a helix, or don't want to go to the trouble, remember that there were no helices in real life...but there were switchbacks.