Jason
Modeling the Fort Worth & Denver of the early 1970's in N scale
jbloch wrote:I'm no expert here, but the idea is that as a track heads into a curve or incline, that one should put in a partial curve before getting into the curve (for curves, obviously), or put in a gradual slope before the actual incline begins (for grades). The idea is to make the directional change (whether horizontal or vertical) less abrupt, as bad things can happen if the change is too abrupt, more likely to happen on tight curves or steep inclines. For example, train rolling on level track, comes to abrupt 3% grade--depending on length of loco/car, the "tilt" that occurs could "uncouple" the leading car/loco from the trailing car, probability of this happening dependant on car length--an easement will dampen this degree of tilt/coupler (vertical) separation effect.Jim
Jim explained it pretty good, but let me add another example. The best way to describe track that lacks easment (horizontal curve) would be the old trainset snap track going from straight to 18 inch radius track. Most of us remember the old train set days, so this analogy should be common enough. When you ran into the beginning of this curve too fast, this was a VERY likely derailment point. That sharp change was probably the biggest culprit in this problem.
An excellent reference with drawings to show the benefits is John Armstrong's Track Planning for Realistic Operation. He does not talk about the grade case, but the same idea applies. Many methods of forming a grade pretty much create an easement without trying, as the roadbed and/or track are not going to want to change grade instantaneaously.
Jeff But it's a dry heat!