49 C.F.R. § 213.327
Track alinement
(a) Uniformity at any point along the track is established by averaging the measured mid-chord offset values for nine consecutive points that are centered around that point and spaced according to the following table:
| Chord length | Spacing |
|---|---|
| 31′ | 7′9″ |
| 62′ | 15′6″ |
| 124′ | 31′0″ |
(b) Except as provided in paragraph (c) of this section, a single alinement deviation from uniformity may not be more than the amount prescribed in the following table:
| Class of track | Tangent/ Curved track | The deviation from uniformity of the mid-chord offset for a 31-foot chord may not be more than—(inches) | The deviation from uniformity of the mid-chord offset for a 62-foot chord may not be more than—(inches) | The deviation from uniformity of the mid-chord offset for a 124-foot chord may not be more than—(inches) |
|---|---|---|---|---|
| Class 6 track | Tangent | 1⁄2 | 3⁄4 | 11⁄2 |
| Curved | 1⁄2 | 5⁄8 | 11⁄2 | |
| Class 7 track | Tangent | 1⁄2 | 3⁄4 | 11⁄4 |
| Curved | 1⁄2 | 1⁄2 | 11⁄4 | |
| Class 8 track | Tangent | 1⁄2 | 3⁄4 | 1 |
| Curved | 1⁄2 | 1⁄2 | 3⁄4 | |
| Class 9 track | Tangent | 1⁄2 | 1⁄2 | 3⁄4 |
| Curved | 1⁄2 | 1⁄2 | 3⁄4 |
(c) For operations at a qualified cant deficiency, E
| Class of track | Track type | The deviation from uniformity of the mid-chord offset for a 31-foot chord may not be more than—(inches) | The deviation from uniformity of the mid-chord offset for a 62-foot chord may not be more than—(inches) | The deviation from uniformity of the mid-chord offset for a 124-foot chord may not be more than—(inches) |
|---|---|---|---|---|
| Class 6 track | Curved | 1⁄2 | 5⁄8 | 11⁄4 |
| Class 7 track | Curved | 1⁄2 | 1⁄2 | 1 |
| Class 8 track | Curved | 1⁄2 | 1⁄2 | 3⁄4 |
| Class 9 track | Curved | 1⁄2 | 1⁄2 | 3⁄4 |
(d) For three or more non-overlapping deviations from uniformity in track alinement occurring within a distance equal to five times the specified chord length, each of which exceeds the limits in the following table, each track owner shall maintain the alinement of the track within the limits prescribed for each deviation:
| Class of track | The deviation from uniformity of the mid-chord offset for a 31-foot chord may not be more than—(inches) | The deviation from uniformity of the mid-chord offset for a 62-foot chord may not be more than—(inches) | The deviation from uniformity of the mid-chord offset for a 124-foot chord may not be more than— (inches) |
|---|---|---|---|
| Class 6 track | 3⁄8 | 1⁄2 | 1 |
| Class 7 track | 3⁄8 | 3⁄8 | 7⁄8 |
| Class 8 track | 3⁄8 | 3⁄8 | 1⁄2 |
| Class 9 track | 3⁄8 | 3⁄8 | 1⁄2 |
(e) For purposes of complying with this section, the ends of the chord shall be at points on the gage side of the rail, five-eighths of an inch below the top of the railhead. On tangent track, either rail may be used as the line rail; however, the same rail shall be used for the full length of that tangential segment of the track. On curved track, the line rail is the outside rail of the curve.