Track Spacing Calculator
Description
On straight, parallel track, a fixed center-to-center spacing keeps cars clear of each other. But on a curve, that same spacing isn't enough: the outer track's cars swing their centers inward, toward the inner track, while the inner track's cars swing their ends outward, toward the outer track — both eating into the same gap at once. Keep the straight-track spacing on a curve and trains can sideswipe each other.
Enter the spacing you'd normally use on straight track, your tightest curve's radius (measured to the inner track's centerline), and the truck center spacing and end overhang of your longest car or locomotive. This calculator adds the extra room both effects need, so you know the minimum spacing to use through the curve — the same two overhang amounts this site's Overhang Clearance Calculator reports, combined into one number for parallel track.
Sources
- NMRA Recommended Practice RP-7.2, "Curved Track Centers" — publishes minimum curved track-center tables for four preset equipment classes, and states that NMRA Technical Note TN-7 "describes the underlying engineering analysis behind the tabulated values." This calculator applies that same underlying overhang methodology directly to the equipment dimensions you enter, rather than looking up one of RP-7.2's four preset classes.
- NEM 104 (MOROP) and NMRA Technical Note TN-7 — the center-overhang and end-overhang formulas themselves; see the Overhang Clearance Calculator's sources for the full citation and derivation of each.
Disclaimer: this is a geometric minimum, not a full safety margin — it uses the inner track's radius for both overhang terms, which slightly over-estimates the outer track's center overhang (a small, deliberately conservative simplification). Add your own clearance margin, and always check against your actual equipment.