the past few years, allowance has been made by several states to allow certain designs of heavy vehicles up to high but they are also restricted to designated routes. In effect, a 4.6 meter high B-double will have to follow two sets of rules: they may access only those roads that are permitted for B-doubles and for 4.6 meter high vehicles. In Australia, both conventional prime movers and cabovers are common, however, cabovers are most often seen on B-doubles on the eastern seaboard where the reduction in total length allows the vehicle to pull longer trailers and thus more cargo than it would otherwise. New Zealand New Zealand legislation governing truck dimensions falls under the Vehicle Dimensions and Mass Rules, published by NZ Transport Agency. New rules were introduced effective 1 February 2017, which increased the maximum height, width and weight of loads and vehicles, to simplify regulations, increase the amount of freight carried by road, and to improve the range of vehicles and trailers available to transport operators. Common combinations in New Zealand are a standard semi-trailer, a B-double, or a rigid towing vehicle pulling a trailer with a drawbar, with a maximum of nine axles. Standard maximum vehicle lengths for trailers with one axle set are: Semi-trailer: Simple: Pole: Trailers with two axle sets can be long, including heavy rigid vehicles towing two trailers. Oversized loads require, at minimum, a permit, and may require one or more pilot vehicles. High-productivity motor vehicle (HPMV) permits are issued for vehicles exceeding 44 tonnes, or the above dimensions. Trucks up to 62 tonnes were allowed, with an initial bridge strengthening program costing $12.5m. Construction Types of trailers There are many types of semi-trailers in use, designed to haul a wide range of products. Box, or dry van Bus Car hauler Intermodal chassis Dry bulk Dump Flatbed Hopper-Bottom Lowboy Refrigerator Reefer Tanker Coupling and uncoupling The cargo trailer is, by means of a king pin, hooked to a horseshoe-shaped quick-release coupling device called a fifth wheel or a turntable hitch at the rear of the towing engine that allows easy hook up and release. The truck trailer cannot move by itself because it only has wheels at the rear end: it requires a forward axle, provided by the towing engine, to carry half the load weight. When braking hard at high speeds, the vehicle has a tendency to fold at the pivot