Step by step
1. Load
Total weight, in tons, of all loaded railcars that will move at once. Use the largest number of cars you expect to move at one time.
2. Rolling resistance
Rolling resistance depends on the condition of the wheel journals, the type of journal lubrication and the ambient temperature. The values below assume journals in good condition and well lubricated.
| Temperature | Running line pull (lbs/ton) |
|---|---|
| Below −20°F (below −29°C) | 25 |
| −19°F to 0°F (−28°C to −17°C) | 20 |
| 1°F to 31°F (−16°C to −1°C) | 15 |
| Above 32°F (above 0°C) | 12 |
Table 1 — Rolling resistance.
3. Grade resistance
Add 20 lbs/ton for each 1% of grade (a 1 ft rise per 100 ft of track).
4. Track curvature resistance
Read the additional running line pull from Table 2 by radius or by degree of curvature. Interpolate for curves not shown.
| Radius (ft) | Degree of curvature | Additional running line pull (lbs/ton) |
|---|---|---|
| 1,146 | 5° | 3.75 |
| 573 | 10° | 7.50 |
| 383 | 15° | 11.25 |
| 288 | 20° | 15.00 |
| 231 | 25° | 18.75 |
| 193 | 30° | 22.50 |
| 166 | 35° | 26.25 |
| 146 | 40° | 30.00 |
Table 2 — Track curvature resistance.
5. Total running line pull
- Load
- tons
- Resistances
- lbs/ton
Worked example
Four railcars at 85 tons each, fully loaded. Lowest anticipated temperature 32°F. Grade 1.5%. Track curvature: chordal factor of 12 in. over 50 ft.
- Load: 4 × 85 tons = 340 tons
- Rolling resistance: 15 lbs/ton
- Grade resistance: 1.5 × 20 lbs/ton = 30 lbs/ton
- Track curvature resistance: 15 lbs/ton
- Total: 15 + 30 + 15 = 60 lbs/ton → 340 tons × 60 lbs/ton
Total running line pull = 20,400 lbs
Quick calculation
For a fast estimate, add:
Allow up to 50% additional line pull for dirty or uneven track.
Rigging
Typical layouts for railcar pullers and positioning systems are in the Railcar Rigging Layouts (Doc 162A, PDF). See also Railcar Positioning.