"automatic half-barrier level crossing" means a level crossing where a road is crossed by a railway and where barriers are installed to descend automatically across part of the road when a train approaches;
"vehicle combination" means a combination of vehicles made up of one or more motor vehicles and one or more trailers all of which are linked together when travelling;
"abnormal transport unit" means—
(i)a motor vehicle or a vehicle combination—
(A)the overall length of which, inclusive of the load (if any) on the vehicle or the combination, exceeds 55 feet;
(B)the overall width of which, inclusive or the load (if any) on the vehicle or the combination, exceeds 9 feet 6 inches; or
(C)the weight of which, inclusive of the load (if any) on the vehicle or the combination, exceeds 32.5 tonnes, or
(ii)a motor vehicle, or a vehicle combination, which in either case is incapable of proceeding, or is unlikely to proceed, over an automatic half-barrier level crossing or an automatic open crossing (R) at a speed exceeding 5 miles per hour; and
"driver", in relation in an abnormal transport unit means where that unit is a single motor vehicle the driver of that vehicle and, where that unit is a vehicle combination the driver of the only or the foremost motor vehicle forming part of that combination.
(b) The requirements conveyed by the sign shown in diagram 649.1 shall be that no abnormal transport unit shall proceed onto or over an automatic half-barrier level crossing or an automatic open crossing (R) unless:—
(i)the driver thereof has himself before the unit so proceeds used a telephone placed at or near the crossing for the purpose or obtaining from a person duly authorised by the railway authority permission for that unit so to proceed;
(ii)such permission has been obtained before the unit so proceeds; and
(iii)the unit so proceeds only in accordance with the terms of that permission
Provided that conditions (ii) and (iii) above shall not apply if—
(A)on the use by the driver of the telephone placed at or near the crossing he receives an indication for not less than two minutes that the telephone at the other end of the telephone line is being called, but no duly authorised person answers it or he receives no indication at all due to a fault or malfunction of the telephone; and
(B)the driver then drives the unit on to the crossing with the reasonable expectation of crossing it within time specified in a railway notice at that telephone as being time between which trains do not normally travel over that crossing.
12.—(1) Where the circumstances so required the indications given by the signs shown in the diagrams in schedule 1 shall or may be varied as hereinafter provided in this paragraph—
(a) any indication given by such a sign may be varied in the respect (if any) in which it is shown below the diagram relating to that sign that the indication may be varied;
