# Influence Surface (Railroad) \[SPIG]

## Live Load Setup

**Rail:** Rail object referencing the rail profile used for this influence surface.

**Live Load Category \[Gravity/Gravity and Centrifugal/Centrifugal/Hunting/Braking]:** Influence-surface category used for this railroad live-load definition.

**Unit Load Spacing Long.:** Longitudinal spacing of the unit loads used to generate the influence surface.

**Centrifugal factor comp. method \[AREMA 1.3.6.c/User defined]:** Method used to compute the centrifugal factor — AREMA 1.3.6.c formula or a user-defined value.

**Max. Design Speed:** Maximum design train speed used in centrifugal-force computation.

**Centrifugal factor:** User-defined centrifugal factor when method is 'User defined'.

**Height of application point (from rail):** Height above the rail at which the transverse force (hunting/centrifugal) is applied.

**Hunting Force Factor (0-1):** Fraction of the wheel load (0-1) applied as the hunting (lateral) force per AREMA 1.3.9.


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