Three legally configured goods-vehicle combinations are being checked: a B-train, an A-train, and a heavy rigid truck towing two other trailers. For the third combination, the rear trailer has a GVM of no more than 3.5 tonnes and the whole combination has an actual gross mass below 20 tonnes. All other applicable requirements are met. All operate within the standard dimension limits in Schedule 2, with no approved dimension variation or exemption (including under a 50MAX proforma), and no load projects beyond the vehicles. What is the maximum overall length for each combination, including its load but excluding collapsible mirrors?
现检查三种依法组成的货运车辆组合：B-train、A-train，以及一辆重型刚性货车牵引另外两辆挂车的组合。第三种组合的最后一辆挂车额定车辆总质量（GVM）不超过3.5吨，整个组合的实际总质量小于20吨。三种组合均满足其他适用要求，并按《车辆尺寸与质量规则》附表2的标准尺寸上限运行，不适用任何获准的尺寸变更或豁免（包括50MAX规定车型方案下的尺寸变更），货物也均未伸出车体。包括货物、但不计可折叠后视镜时，这三种组合各自的最大总长是多少？
20 metres for each of the three combinations under the stated conditions, not only for the B-train.
在题述条件下，三种组合的最大总长均为20米，并非仅B-train适用。
阅读相关知识
A B-train has two semi-trailers, with the second coupled to a fifth wheel at the rear of the first. An A-train has a semi-trailer towing a full trailer. The other two-trailer arrangement in this question requires a heavy rigid goods vehicle, a rear trailer with GVM no greater than 3.5 tonnes, and actual gross mass of the whole combination below 20 tonnes. These conditions do not replace other coupling, axle, mass, stability or licensing requirements. The 20-metre answer is for the stated operation: certain reduced-width loads projecting behind a rear full trailer can have a different overall-length limit, and overdimension or special-permit operation must be checked separately.
B-train由两辆半挂车组成挂车部分，第二辆半挂车通过第一辆后部的第五轮连接装置连接。A-train的挂车部分为一辆半挂车牵引一辆全挂车。本题中的另外两挂车结构要求牵引车为重型刚性货运车辆，最后一辆挂车的额定车辆总质量（GVM）不超过3.5吨，整个组合的实际总质量小于20吨；这些条件不替代其他连接装置、车轴、质量、稳定性或驾照要求。20米答案仅针对题述运行条件：某些从最后一辆全挂车后部伸出的限宽货物可适用不同的总长上限；超尺寸或特殊许可运行需另行核查。