Locher set out to design a rack system that could be used on gradients as steep as 1 in 2 (50%). The Abt system — the most common rack system in Switzerland at the time — was limited to a maximum gradient of 1 in 4 (25%). Locher showed that on steeper grade, the Abt system was prone to the driving pinion over-riding the rack, causing potentially catastrophic derailments, as predicted by Dr. Abt. To overcome this problem and allow a rack line up the steep sides of Mt. Pilatus, Locher developed a rack system where the rack is a flat bar with symmetrical, horizontal teeth. Horizontal pinions with flanges below the rack engage the centrally-mounted bar, both driving the locomotive and keeping it centered on the track.