Jacobs bogie

A Jacobs bogie is a single four-wheel or six-wheel truck positioned beneath the junction between two adjacent passenger cars in an articulated train set. Instead of each car having its own pair of bogies, the trailing end of one car and the leading end of the next car both rest on the same bogie frame. This arrangement saves weight, reduces unsprung mass, and lowers the floor height of the train, making boarding easier.

The design appears most commonly in European articulated trams and electric multiple-unit (EMU) trains. The bogie itself is mechanically identical to a standard truck: it carries two axles, suspension components, and brake equipment. What differs is its position and the fact that it must support two car bodies instead of one. The connection points are typically pivot-mounted, allowing each car body slight independent movement while the bogie remains fixed in space.

Weight and floor height advantages

By eliminating one complete bogie per articulation point, a three-car set saves the equivalent of one full truck assembly: roughly 4,000 to 6,000 kg depending on the design. This reduction cuts traction power requirements and improves acceleration and braking. The floor level can be dropped lower at the articulation because there is no truck beneath the joint; modern low-floor trams exploit this benefit to bring the platform height down to 350 mm or lower at these points.

The trade-off lies in maintenance complexity and passenger comfort. A bogie failure at the joint affects both vehicles simultaneously, potentially taking two cars out of service. Ride quality around the articulation point can suffer if pivot bearings wear, creating a noticeable bump that passengers feel. The bogie itself must be engineered to handle lateral loads from both cars during tight cornering.

The term honours Valérien Jacobs, a French railway engineer whose patent on this arrangement was filed in the 1930s. The design became standard in post-war European tram engineering and was later adopted for articulated passenger trains. Modern variants use either two or three axles; the three-axle version distributes loads more evenly and is favored for heavier duty applications, though it increases unsprung mass.