Converting a coverage route system to PolyLineM shapefile can create duplicated vertices or extra parts.
The ArcCatalog/ArcToolbox coverage to shapefile conversion tools use the ArcInfo Workstation defined layers LAYEREXPORT command to create a shapefile. This code has not been optimized to reduce the number of vertices and parts.
Use ArcMap to export a coverage route system to shapefile. ArcMap uses the FeatureDataConvertor object behind the scenes. This object has code that has been optimized to reduce the number of vertices and parts.