SpeedType

Flag:	SpeedType
File(s):	rules(md).ini
Values:	special strings
Default:	Foot for InfantryTypes, Wheel for VehicleTypes, Winged for AircraftTypes and Float for BuildingTypes
Applicable to:	InfantryTypes, VehicleTypes, AircraftTypes, BuildingTypes (to the same extent as Locomotors do)

SpeedType defines the way units move over certain terrain types. Looking at the rules, we see that each terrain type (Clear, Rough, Road, Tiberium, Water, etc.) has it's own section. Let's look at one:

[Clear]
Foot=100%
Track=100%
Wheel=100% ¹
Float=0%
Hover=50%
Amphibious=80%
FloatBeach=0%
Buildable=yes

The numbers indicate at what percent of it's Speed= can the unit with a certain SpeedType= move over this terrain. You see that units with SpeedType=Hover, for instance, can move only up to half their normal Speed= over this terrain. You can use percent over 100, it'll just revert to 100.

Note that the AircraftType's default SpeedType=Winged will always result in 100 percet movement ability.
Winged can not be modified in the terrain type's section (i.e. Winged=80% would not work).

The terrain type of a certain tile is set in the tile .tmp file.
Terrain types are as follows:

Terrain Types

• Clear - Clear ground, no obstacles.
• Road - Dirt or paved roads.
• Rough - Rougher terrain such as rocky areas or thick grass. In RA2, this defaults to the same settings as Clear.
• Rock - rocks, trees, cliffs, anything impassable.
• Tiberium - areas covered in Ore/Gems/Tiberium.
• Water - Water as in rivers or ocean areas.
• Railroad - Train tracks (Works in TS, in RA2 requires Terrain Expansion (aka TX)).
• Tunnel - Tunnel Entrance/Exit (Works in TS, in RA2 requires Terrain Expansion (aka TX)).
• Beach - The line where water and ground join.
• Weeds - Tiberium Veins (Works in TS, in RA2 it is not assigned to anything and can be used for new movement rules).
• Ice - Water gone cold (Works in TS, in RA2 it is not assigned to anything and can be used for new movement rules).
• Wall - duh, non-firestorm/non-laserfence walls.

Notes

¹ - SpeedType=Track is not used by any object ingame. So you can either restore it for it's original purpose (tracked vehicles) to provide certain variation against standard vehicles (the vehicle locomotor defaults to SpeedType=Wheel) (see also Tracked vs Wheeled), or use it for something entirely unrelated, like a class of vehicles that can't go over tiberium for whatever reason.
² - You can make overlays which, when placed, transform the ground (technically) to any type mentioned above. To do that, use the Land=<terrain type name> tag on the overlay rules coding.

According to Allied General, Track was originally used for trains.