inclines
Mr Planeshavings,
Ah ha! Now I understand!
What you are referring to is an "incline" and whether your locos will haul you load up the hill!
It depends on a lot of things, but the general rule of thumb is to not make your incline (rise to the bridge) more than 2% -3%. ie, for every 100 inches of track, you should rise more than 3 inches. The larger/longer the load, the less the incline should be.
This subject has been tossed around in many threads in here. If you click on the "search" button, and use "incline" as a word to search for, you will see quite a few posts/threads on the topic.
I run nearly a 5% incline and it is toooooooo steep. At first, the locos would slip when hauling to load up the hill, so I was using two locos. Using some wet/dry emery paper (to clean the tracks) after a while, I found that one loco was enough and it didn't slip anymore. However, the speed is considerably slowed, and it then races down the other side. I run a 5 passenger car consist over the steepest incline, and 8 passenger cars over the less steeper one.
For some very good helpful info, do the search on "incline" (full text search). You will find the info useful.
Another thing you MUST consider too, with inclines is to "transition" them.... in other words, make the change from level to slope a gradual one over a distance of 12"- 18" or so. Long rollingstock WILL derail if you go from level track straight to the angle of the desired incline, and it will look unrealistic too.
Your locos will be fine on any incline, but, will sit there and wheelspin if the incline is too steep, when hauling a decent load.
Some locos are better at inclines than others, especially the "all wheel drive" locos. There should be no need to use anything other than your Athearns, if your inclines are kept to a reasonable steepness.