Some practical advice I would offer would be as follows:
(a.) drive right into the parking garage that is right next to the Steamtown acerage. You will be able to walk from the 2nd Floor of the attached mall to go right out onto a pedestrian bridge that reaches directly into the train yard. Plenty of food places are in the mall for snacking.
(b.) you can enter the whole Steamtown yard via the pedestrian bridge which ends in the RRyard with a gradual sloped walkway that will take you down to the ground right near the Big Boy that is featured outside there. The bridge affords you broad perspective on the whole exhibit and provides a view directly down onto passing trains under it, on occasion. (However, don't make the mistake of standing there, looking downward, when a steam engine passes beneath you - what a hot face-full I got 
!!!)
Using the pedestrian bridge is how I accessed and explored the place, which required less walking than entering from street-level, a few years ago. My suggested plan for approaching the exhibit tries to give your companions a bit of a break on the distances to be walked.
FrankM
