# 20559: How does FBS calculate the parking braking percentage (required parking brake effect, "Sawing lines" in the driver's timetable)?

In contrast to the calculation of the minimum braking percentage, the gradient is not used for the required parking brake effect ("sawing lines") over a longer distance, since kinetic energy does not have to be reduced, but the train is already standing. Actually, it would be the most appropriate to use the maximum *effective slope* over the precise train length and train composition. The only problem is that, in most cases, the train composition and thus also the length are not certain. Even in the case of travel trains, short-term shortening of the train, in extreme cases theoretically to one wagon, is possible or at least technically permissible. This means that practically every train can have a certain minimum length - engine and one wagon or two engines - cannot be excluded. (Single engines and multiple units do not need to be considered here, since the question of the number of hand brakes to be attracted is less relevant in these cases.)

If the minimum train length is close to 0, the actual gradient could also be used to calculate the required parking brake effect ("saw lines"). For a length of 0, the actual gradient and the effective gradient are identical. In the DB Directive 457.0401.2 (3) ("Determining the most suitable slope for the sawing lines"), the use of the average inclination with a minimum section length of 50 m is specified. FBS therefore uses the effective gradient of a 50 m long line (that means a 50 m long homogeneous train). This is somewhat more correct than using the actual slope at 50 m minimum length; but the difference is minimal. There is only a difference if tilt changes are closer to each other than 50 m

In most driver's timetables, the required parking brake effect is represented by a certain number of "saw lines". The conversion of the gradient into a number of sawing lines is format-dependent. In most formats, one saw line per complete 10 ‰ (that means number of saw lines = rounding down (slope / 10)) with a maximum of two or three saw lines. This rule must always be viewed in conjunction with what the driver has to do, depending on the number of sawing lines (see topic # 40238).

Last update on 19.03.2020 by iRFP Support.