article 4 + 4.  In this Order:

term motorcycle + “motorcycle” means a mechanically propelled vehicle having less than four wheels and, in a case where a cabin is provided, the cabin of which is not so constructed as to enclose the driver and any passenger;

term the tunnel crossing + “the tunnel crossing” has the same meaning as in article 2(1) of the River Tyne (Tunnels) Order 2005.