A back-up featherer is provided for an engine arrangement. This invention also provides a method of inhibiting polymerization of hemoglobin which comprises contacting the hemoglobin with an amount of an antiviral agent effective to inhibit polymerization of the hemoglobin, so as to thereby inhibit polymerization of the hemoglobin. It is desirable that the motor torque not exceed the rider torque; otherwise the motor overpowers the rider. Since the road line is not displayed on the photographic map, the information items other than the road line are easily recognized.