used for windows 27 this increases passenger safety and reduces system maintenance costs within reasonable limits the vehicle shape is designed to reduce aerodynamic drag since this is really the only road load on the wheel less vehicle doors 26 are simple and non jamming even under conditions of a stackup of vehicles the doors 26 do not open outward as in the usual passenger automobile they are on the inside and slide to the side an interlock switch prohibits the vehicle from leaving station slots 66 until the two doors 26 are closed although lsm and lhia permanent magnet fields are shown in the drawings as flush or smooth with the bottom of the vehicle they would actually have the bottom surface covered with a thin sheet of non metallic material such as teflon or encapsulated with material to prevent the collection of metallic particles except on the pole faces in order to keep the undersurface clean the on ramps would contain brushes in the guideway surface to knock off and trap iron particles as the vehicle passes over the brush if the permanent magnet field assembly 13 were used as depicted in fig1 a b amp c without other protection the pole saliencies 15 would attract ferrous particles which would eventually build up in sufficient volume to bridge or partially bridge between the poles 15 and cause excessive flux leakage or weakening of the main air gap useful flux thereby degrading the performance of.