$IV, $INITIAL_SPEED, $STARTSPEED

When a vehicle starts, it begins to move with this speed - and it accelerates according to its acceleration value, either specified in the movement's parameter, or from the default value inherited from the segment hierarchy.

The vehicle can move only a whole pixel. If the initial speed is too low, you will see single 1-pixel wide "jumps" at the beginning of the movement. Conversely, when it is set too high, the vehicle starts to move abruptly as if it were a Formula 1 racing car.   Ultimately, this setting should be set to the user's preferences.

Normally, you will want to use the command form to set this parameter; to set the value you find pleasing to the eye one time for the whole timetable file. The default value of one pixel is usually considered acceptable to most people.