A shapefile is just like a CSV file, but each row also has a geometry shape. The columns are totally arbitrary and could be anything. That's the "shapefile spec". How are roads stored? What about highways/motorways with 2 carriageways? Is that 2 one way lines, or 1 line through the middle? Is the name of the road given in the shapefile? What column stores it? "NAME"? What about the speed limit? "MAXSPEED"? "SPEEDLIMIT"? What units is that speed limit in? mph? kmph? What about having a textual speed limit definition, then you'd have to parse "30 M.P.H." as a speed limit. etc. etc. etc.