Gear

From Simutrans Wiki

The gear is a factor applied to the nominal power of a powered vehicle (same as its real-world power, if the vehicle has been taken from there), to get the effective power that is used in the game (to achieve a realistic behaviour).

In the game, it is shown as a fraction ("0.50:1" means: use half of the nominal power). If it's not shown (<=> not specified for the vehicle), the default gear (1:1) is used. In Dat/Pak files (optional parameter "gear"), it is encoded in percent.

Tractive effort or maximum acceleration (as typical for a given vehicle) aren't used as parameters in the game; instead, the program uses its own physical model of movement, using effective power and the drag value, to achieve a behaviour matching the other parts of the game.