Marlow By-pass Bridge , Marlow , ( A404 ) 49.10 Maidenhead R'way Bridge (GWR to Bristol) 46.67 M4 Bridge 38.91 Windsor Bridge , Eton & Windsor 28.46 River Colne (Upper mouth) 28.45 Runnymede Bridges , Staines ( A30 & M25 ) 27.70 River Colne (Lower mouth), Staines 21.34 M3 Bridge ,