using transformers for the cancellation of the earth leakage current. As is the case for all symmetrical powerlines there are also at traction power lines twisting points. A traction powerline for one circuit has usually two conductors. Since most traction current lines possess two electric circuits, four conductors are on the pylons as a rule (in contrast with three-phase alternating current lines, whose number of conductors are an integral multiple of three). Routing of traction current lines Traction current lines are not usually laid parallel to the railway line, so as to minimise the line length and to avoid unnecessary influences of electrical system near the railway line. However, there are cases where this practice is not followed (for example, the current supply of some rapid-transit railways operating with alternating current in Germany). In this case, the traction current line is laid on special cross beams of the overhead wire pylons above the overhead line. Because overhead line pylons possess a smaller cross section than traction current masts, these cross beams have to be quite narrow, so the arrangement of four conductor cables in one level, which is standard at traction current lines, cannot be used. Where four conductors are needed, one approach is to employ a two-level arrangement of conductor cables. Alternatively, in cases of double-tracked railway lines, the overhead line pylons for both driving directions are equipped with cross beams for the traction current system (two conductor cables). In densely populated areas, where rights of way are rare, it is common to find pylons which carry electric circuits for traction current as well as those for three-phase alternating current. The latter can be 110 kV, 220 kV, or, in some cases, 380 kV three phase AC lines. In such cases, the traction current lines must use insulators which can cope with the maximum peak-to-peak voltage which can occur between the lines. Traction current lines are implemented as a rule as single leaders. For the supply of railways with much rail traffic and in particular for the power supply of high speed railway lines such as the German ICE (Inter City Express) trains, conductors of two bundles are used. The traction current lines from the nuclear power station at Neckarwestheim to the traction current switching station at Neckarwestheim, and from the traction current switching station at Neckarwestheim to the central substation in Stuttgart Zazenhausen are implemented as four-bundle conductors.