The present invention relates to an asymmetric porous polytetrafluoroethylene membrane comprising a dense skin layer and a continuously foamed porous layer, the dense skin layer having a surface roughness Ra of 20 to 165 nm; the dense skin layer having a contact angle for water of 120 to 135\xb0; the porous layer having a maximum pore diameter of 0. An apparatus may include a media access control processor to monitor interference levels for a receiver, estimate throughput values for each interference level, and select a data rate based on the throughput values. Upon arrival of the moving object at the guide point, a first turn guide icon and a second turn guide icon are determined for the guide target, wherein the first turn guide icon and the second turn guide icon collectively represent suggested vehicle operations at the guide point and a drive direction at a position of the guide target from a plurality of previously stored turn guide icons.