Railroading 101
Bob Ciminel
Founder and Moderator – Montour RR and PRR Panhandle PA Discussion Groups
Part 1 – Track
Anyone who walks or rides on the Montour or Panhandle Trails is actually using the railroad’s original subgrade, or roadbed, which is the prepared earth surface on which the track is constructed.  The subgrade defines the physical layout of the railroad in terms of elevation, grades and curvature, and where the cuts, fills, bridges, and tunnels are located.
The subgrade is a very dense, compacted, stable surface, shaped to allow surface water to drain away so that it doesn’t soak in and create soft spots.  In places where the subgrade would act as a dam across an existing water channel, culverts, bridges, and trestles are built.
Once the subgrade is built, a layer of crushed rock, called subballast is laid down to improve drainage and distribute the weight of the track.  A second layer of crushed rock or ballast is then laid and tamped under and around the ties, extending beyond their edges to form a ballast shoulder.  The ballast provides both horizontal and vertical stability, drainage, and distributes the weight of the trains running on the track.  The condition of the ballast is one of the major factors that determine the speed at which trains are permitted to operate on the track.
The track rests on crossties, or ties, that keep the rails in alignment.  For the past 100 years, ties were made of 6x6-inch or 9x9-inch solid timbers preserved with creosote, made from coal tar.  Ties used for standard gauge track (4 feet, 8.5 inches wide) were 9 feet long.  Beginning about 50 years ago, some railroads began using concrete ties, which have become the predominate type of tie used on track with heavy traffic.
Tie plates are used to fasten the rail to the ties.  The tie plates have shoulders to hold the rail in place and holes for spikes that are driven into the ties.  The spikes are square and have a specially-designed offset head that holds the rail down against the tie plate.  In curves, rail anchors are attached on each side of the tie plates to keep the rails from moving.
Rails are made of steel rolled into a T-shape.  The top of the rail is called the head, which rests on the web and the base.  The inner part of the web is called the gauge side; the outer part is called the field side.  Rail is designated by its weight per yard, which can vary between 75 and 136 pounds per yard.  Lightweight rail is used on branches and sidings; heavyweight rail is used on main tracks.  Rails are stamped to identify the mill where they were manufactured, as well as the year and month (designated by a series of 1s) the rail was rolled at the mill.  For example, a rail stamped CAR 1905 1111 would have been rolled by Carnegie Steel in April 1905.  Prior to the development of continuous welded rail, the standard rail length was 39 feet long to allow transporting it on 40-foot flatcars.
Each end of a rail was drilled with two or three holes that allowed the rails to be bolted together with four- or six-hole joint bars.  The rail joints were the source of the familiar clickety-clack sound made by trains. 
Railroad curves are measured in degrees, with one degree of curvature being the change in direction over a distance of 100 feet.  A 10-degree curve is considered very sharp and would have a radius of 573 feet.  High-speed transit lines, such as those used in Europe and Japan, typically have curves of 30 minutes or a radius over two miles long.  Curves may also be super elevated, or banked, so that the outer rail is slightly higher than the inner rail, which allows trains to go around them at higher speed.  For example, a one-degree curve with no super elevation can be negotiated at 66 mph.  By adding three inches of super elevation, the same curve can be negotiated at 93 mph.
The sharpest curve on the Montour main track, according to an undated track diagram, was a 10-degree curve at Milepost 7.5 between the east end of Lotus siding and the west end of Cliffmine siding.  However, the Library Branch had consecutive 10-degree right, left, and right curves at Library Viaduct.  On the Panhandle main track, the sharpest curve between Milepost 0 and the state line at Collier was a 9-degree curve on the west leg of the wye coming off the Panhandle Bridge at Monon Tower.
Grade is also measured in degrees, with one degree of grade being the change in vertical elevation over a distance of 100 feet.  A grade of 3 percent is considered an extreme grade for a railroad.  For example, a train that has sufficient power to run 50 mph on level track will run at less than 20 mph on a 1-percent grade.  The Saluda Grade (no longer in service) on the Norfolk Southern near Spartanburg, SC, is the steepest mainline grade in America with an official grade of 4.7 percent.  Near the end of track at Bald Knob on West Virginia’s Cass Scenic Railroad, the grade reaches 11 percent, necessitating the use of gear-driven locomotives.
The steepest grade on the Montour main track was 1.76 percent at the western end of Greer Tunnel.  However, not to be undone, the Library Branch had a 2.44 percent grade between Milepost 0.7 and 1.8 where the branch joined the main track at Library Junction.  The Panhandle was able to limit its grades in Pennsylvania to a maximum of 1 percent, with the longest stretch being the 1.5-mile long ascent of Bulger Hill between Midway and Bulger Interlocking.
Railroad tracks provide two important characteristics that make railroads unique, the need for very low energy to provide propulsion and very long stopping distances.  The curvature of the rail head limits contact with the conical surface of the train’s wheels, thus posing little resistance (friction) to movement.  The contact area is about the size of a person’s finger, even though it can support weight as high as 18 tons.  Rolling resistance is so small that one horsepower can move one ton at over 40 mph on level track.  However, this same minute amount of friction also results in a 10,000 ton train taking a mile or more to stop from 40 mph.
(Reference: Elements of Train Dispatching, Volume 1 by Thomas White, VTD Rail Publishing, Mountlake Terrace, WA, 2003)