Track Section Description (Input Form 8C)

When train performance Option 1 or 2 is being used, each route must have associated with it a description of the track curvature, grade, maximum allowable train velocity that occurs along the route, energy sector number and coasting parameter. The train route is divided into lengths, called track

sections, over which these parameters remain constant. These track sections are not to be confused with the line sections required for the aerodynamic simulation. A change in any of the five parameters - track curvature, grade, maximum allowable train speed, energy sector number, or coasting parameter -necessitates the formation of another track section.

A forward end and a backward end must be defined for each track section. These ends are defined with respect to the route coordinate system which starts at the route origin and increases in the

direction of train movement on that route. The backward end of the track section is the end which is located closest to the route origin, and the forward end of the track section is the end which is located furthest from the route origin and has the higher coordinate upon the route coordinate system.

Figure 7.5 shows a route which consists of four track sections. The track sections are numbered in increasing order in the positive direction with respect to the route coordinate system. The first track section is situated with its backward end at the route origin (location 0.0) and its forward end further along the route. The backward end of the second track section is coincident with the forward end of the first track section. The route is defined from the route origin to the forward end of the last track section. Track sections are defined by giving the location of the forward end of the track section. This location is the coordinate, in feet, along the route coordinate system. The length of the Nth track section is equal to the location of the forward end of track section N minus the location of the forward end of track section N-1. However, the first track section begins at the route origin and extends to the location of its forward end. The location of the track section boundaries must be given in feet measured along the track. This is the actual distance that a train operating on that route would travel, and this distance would differ from the horizontal distance if the route contains grades or curves.

The user must determine the number of track sections that are required to describe a route and then proceed to describe each of the track sections. The track sections are described in increasing order, beginning at the route origin and continuing in the positive direction along the route. Trains operating on a route are removed from operation on the first complete train evaluation (defined in Section 10.11; in most cases, 1 second) after the front of the train has gone beyond the location of the forward end of the last track section. With this in mind, a route which exits a tunnel system through a portal should be extended at least one train length beyond the portal. This will allow the train to completely exit the portal before it is removed from operation. If the route is not continued far enough past the portal, the train will be removed from operation while it is exiting the tunnel, and the airflow will be affected by a sudden drop in the train forcing function.

Routes which terminate within the tunnel system should have the forward end of the last track section located at the place where the train is to be removed from operation. This might be a short distance, for example 20 feet, from the physical end of the tunnel. (The user is reminded that dead end tunnels cannot be simulated by the SES program.) The allowable speed in the last track section should be low, so that the train approaches the terminal point slowly. To prevent a violation of airflow continuity within the system, a new train should be placed in operation for each train that is removed from operation within the system. This train should be placed in operation at exactly the same physical location in the system that the corresponding train is removed from operation. (This alignment problem is reduced if the process of removing trains from operation and placing new trains in operation is done entirely within the same line

7-11 operation and a train is placed into operation at the same location but traveling in the opposite direction on a different route.

TRACK SECTION 1

TRACK SECTION 4 TRACK

SECTION 3 TRACK

SECTION 2

DIRECTION OF TRAIN MOVEMENT ROUTE ORIGIN

KEY:

F = THE FORWARD END OF THE TRACK SECTION B = THE BACKWARD END OF THE TRACK SECTION B F B F B F B F

+ 0 500 1000 1500 2000 2500

ROUTE COORDINATE SYSTEM, FT

Figure 7.5 Track Section Relationship to Route Coordinate System

Radius of Curvature. Horizontal curves are usually constructed as portions of a circle. The amount of curvature is measured by the radius of this circle. That is, a sharp curve would have a small radius and gentle curve would have a long radius. Track curvature is a parameter which is used by the train performance subprogram since an additional amount of train resistance is experienced by trains as they round curves. This additional train resistance is caused by increased friction of the wheels on the rails. For properly banked curves, it is inversely proportional to the radius of curvature. The additional train resistance which is caused by the train rounding a curve is small compared to the rolling resistance and other resistances that act upon a train. Often a spiral will be used as a transition between the straight section of track and the curved portion. For defining the track sections the spiral may be ignored with the boundary between the straight and curved portions of track at the midpoint of the spiral. A straight section of track, sometimes referred to as tangent track, is a curve of infinite radius. To represent this, a

convention has been established by which a curve radius of zero feet (0.0) is interpreted to mean that the track is straight. All other curve radii are entered by giving the radius length in feet.

Grade or Elevation of Forward End. For each track section, the track grade may be entered. This grade may be positive (uphill) or negative (downhill). The grade for each section may be entered as a percentage or as an elevation of the forward end of the track section. If the percentage grade is available from the plans, the grade would be preferred rather than elevations.

The elevation of the forward end of the track section is given in feet and may be measured with respect to an arbitrary datum. The grade of a track section is the difference in elevation between the forward end and backward end of the track section divided by the horizontal distance (the length of the track section is actually the sloping distance or the hypotenuse of the triangle).

Elevations may be either positive or negative indicating that they are, respectively, either above or below the datum. It is usually best to set the datum below the lowest point and use only positive

elevations. This eliminates sources of user error which can occur from manipulating numbers of different sign. All elevations must be either greater than +0.1 feet or less than -0.1 feet. When an elevation is entered as zero or close to zero, the program uses the number which is entered as the grade.

Consequently, an elevation of zero cannot be entered. When the elevation of the forward end of the first track section is entered, this same elevation is taken as that of the backward end of the first track section and the grade is equal to zero. The second and subsequent track sections use their elevation with the elevation given for the previous track section to compute the grade.

Maximum Allowable Train Velocity. For each track section, the user must enter the maximum train speed at which the train may operate in the track section. This speed will not be exceeded by the train, but the train will attempt to speed up to this limit with one exception. The exceptional case occurs when coasting has been specified for a track section and, if the train reaches the minimum speed restriction within that track section, the option to remain at the minimum speed has been designated.

Energy Sector Number. A tabulation of the energy consumed by train propulsion and auxiliary systems is made for each energy sector. One or more track sections can be located in an energy sector, and the track sections within the same energy sector need not be contiguous. The energy sector numbers may range from one (1) to LMSTR, which is given in Appendix A. An entry of zero for an energy sector number indicates that an energy tabulation is not required for that track section. See Section 10.9 for further details on the Train Energy Summary Output.

Coasting Parameter. If train performance option 1 is being used, coasting can be designated within a track section. For each track section permitting coasting, the user must enter a 1.0 for the coasting parameter; otherwise, a 0.0 must be entered.

Example 7.2. The route must be divided into track sections, each of which is a length of track over which the grade, curvature, maximum allowable train speed, coasting parameter and energy sector number are constant. Figure 7.6 shows an example of how track section data would be prepared for a route on which coasting is not permitted. The portion of the route which is shown is divided into ten track sections. If coasting were permitted, for example, on track sections 2 and 3, the total number of track sections would remain at ten. However, if coasting were permitted only for a portion of track section two, the user would have to enter each portion as a separate track

TRACK SECTION NUMBER 1 2 3 4 5 6 7 8 9 10 LOCATION OF FORWARD END

OF TRACK SECTION 2550 3000 3200 3500 3600 4150 4400 4620 5000 5500

GRADE, PERCENT 0.0 -2.0 -3.0 1.0 1.0 0.0 -2.8 -2.8 -2.8 -0.5

CURVE RADIUS, FT 0.0 9800 9800 9800 3700 3700 3700 900 900 0.0

MAXIMUM ALLOWABLE

TRAIN SPEED, MPH 65 65 65 65 65 65 50 50 50 50

ENERGY SECTOR NUMBER 1 1 1 2 2 2 2 2 3 3

LOCATION OF FORWARD END OF TRACK SECTION

SAMPLE PROGRAM INPUT CORRESPONDING TO THE ABOVE TRACK SECTIONS

Figure 7.6 Sample Data Describing Track Sections

1 2 3 4 5 6 7 8 9 10

2000 2550 3000 3200 3500 3600 4150 4400 4620 5000 5500 GRADE 0% -2.0% -3.0% 1.0% 0% -2.8% -0.5%

CURVATURE STRAIGHT 9800’ 3700’ 900’ STRAIGHT

MAXIMUM SPEED 65 MPH 50 MPH

ENERGY SECTOR NO.1 NO.2 NO.3

The user defines a number of track sections for each route, and to the user-defined track sections is added an additional number of track sections which are internally created by the SES Program. The total of the user-defined and internally created track sections must not exceed the array size limit for the number of track sections for a route.* If this limit is exceeded, the user may either reduce the number of track sections that has been defined by combining adjacent track sections, or expand the program array size by the procedure outlined in the SES Programmer's Manual.