VICTORIA — Following the example of other Canadian jurisdictions, the Commercial Vehicle Safety Enforcement Branch of B.C. has increased the allowable axle weight threshold for ‘reversed B-trains’ up to 23,000 kg under certain conditions.

A reversed B-train is a heavy vehicle combo of a tractor and two semi-trailers, where both trailers are coupled by “highly mounted” fifth wheels (pivoting plate is horizontal above the trailer tires) and the latter trailer has a tridem axle group.

Under the Transportation Association of Canada’s memorandum of vehicle Weights and Dimensions, reversed B-trains are permitted provided that the fifth wheel is no more than 0.3 m behind the rearmost axle of the first trailer.

However, the MOU had been unclear as to what weights would be allowed on the second trailer. B.C.’s interpretation of the MOU had been to cap the tridem group on the rear trailer to 17,000 kg.

With the amendment to the province’s Commercial Transport Regulations, the tridem axle group will be allowed on the second trailer of a reversed B-train with a maximum of 21,000 kg with axles spread between 2.4 m and 3 m; and a max of 23,000 kg for a tridem spread between 3 and 3.1 m.

The allowance is in effect provided that fifth wheels are all highly mounted; and the center of the fifth wheel is located longitudinally between the suspension spread of the first trailer or not more than .03 m behind the rearmost axle on the lead trailer.

All other requirements such as the minimum trailer wheelbase and interaxle spacings applicable to conventional B trains also apply to reversed B-trains.

“Underslung” fifth wheels located on either the truck or first semi-trailer are now permitted on reversed B-trains, says CVSE of B.C.