Bogie exchange is a system for operating railway wagons on two or more gauges to overcome difference in the track gauge. To perform a bogie exchange, a car is converted from one gauge to another by removing the bogies or trucks (the chassis containing the wheels and axles of the car), and installing a new bogie with differently spaced wheels. It is generally limited to wagons and carriages, though diesel locomotives can be exchanged if enough time is available.
Bogie wagons can have their gauge changed by lifting them off one set of bogies and putting them back down again on another set of bogies. The pin that centres the bogies and the hoses and fittings for the brakes must be compatible. A generous supply of bogies of each gauge is needed to accommodate the ebb and flow of traffic. The bogies and wagons also need to have standardized hooks, etc., where they may be efficiently lifted. The two wheel sets on four-wheel wagons can be changed as well if the wagon has been designed accordingly.
Steam engines can be designed for more than one gauge, by having, for example, reversible wheel hubs that suit two alternative gauges. This was done in the 1930s and beyond in Victoria for possible gauge conversion, though no engines were ever converted in this manner other than one heritage engine (R766). Some 1,000 mm (3 ft 3 3⁄8 in) metre gauge Garratt locomotives of East Africa were designed for easy conversion to 3 ft 6 in (1,067 mm) gauge, though again none ever was.
In 1944, the LMS re-gauged a pair of "Jinty" 0-6-0 tank locomotives - originally built to UK 4 ft 8 1⁄2 in (1,435 mm) standard gauge - for use on its 5 ft 3 in (1,600 mm) gauge Northern Counties Committee (NCC) lines in Northern Ireland; re-designated as Class Y, they largely undertook shunting work on dockyard lines in Belfast. The re-gauging was performed by simply reversing the wheel centres so that the spokes dished outwards.
Diesel locomotives have bogies like wagons and carriages, only with more cables for the traction motors and take a little longer to convert. In Australia, some classes of diesel locomotives are regularly gauge-converted to suit traffic requirements on the 1,435 mm (4 ft 8 1⁄2 in), 1,600 mm (5 ft 3 in), and 1,067 mm (3 ft 6 in) networks.
Since the 1,067 mm (3 ft 6 in) networks are not all connected to each other, being separated by deserts or lines of other gauges, they are bogie-exchanged or piggybacked on road or rail vehicles when transferred between these networks.
The simplest way to carry out bogie exchange is to lift the wagons off the bogies and replace them back on new bogies. This may require the wagons in a train to be uncoupled, and continuous brakes disconnected. As the bogies are swung out of the way, they sway, which wastes time settling them down.
Another way of carrying out bogie exchange is to lower the bogies onto a trolley in a pit, after which the trolleys are rolled out of the way and others return. This keeps the train couplings and continuous brakes connected. In addition, the bogies never need leave a solid surface, so they can be wheeled in and out more quickly. This method was used at Dry Creek railway station, Adelaide.
Between 1961 and 1995, Australia had five bogie exchange centres, which opened and closed as gauge conversion work proceeded. The gauges served were 1,435 mm (4 ft 8 1⁄2 in) and 1,600 mm (5 ft 3 in), though the 1,067 mm (3 ft 6 in) Queensland did acquire 100 bogie-exchange compatible QLX wagons just in case. All the wagons involved had wagon codes ending in "X", such as VLX.
The centres were:
The busiest facility was that at Dynon, in a typical year (1981–82), 24,110 wagons were bogie exchanged, an average of 66 per day. This was done by one shift of 18 men, compared with the 100 men required if the same amount of freight were transferred wagon to wagon.
Bogie exchange was used between 2 ft 6 in (762 mm) and 1,000 mm (3 ft 3 3⁄8 in) gauge on the Ferrocarril de Antofagasta a Bolivia Railway.
A bogie exchange station exists at the Chinese border to Mongolia. Both the Moscow-Beijing passenger train (Trans-Siberian) and freight trains get their bogies exchanged. Mongolia has Russian gauge 1,520 mm (4 ft 11 27⁄32 in), China has 1,435 mm (4 ft 8 1⁄2 in). Also, a bogie exchange station was placed farther east at the Russian–Chinese border crossing at Zabaykalsk/Manzhouli.
A bogie exchange station exists in the Port of Turku with a short stretch of 1,435 mm (4 ft 8 1⁄2 in) gauge railway. Freight cars get their bogies exchanged. SeaRail train ferries go from Germany and Sweden. They carry no passenger trains, and passengers must walk by foot to Turku Harbour railway station opposite the ferry terminals. Finland has 1,524 mm (5 ft) broad gauge.
The bogies of the direct sleeping car Moscow – Pyongyang, which runs twice monthly, are exchanged there. 
Bogie exchange conversion times were:
Variable-gauge axles in an automatic track gauge changeover system (ATGCS) is a newer and faster development than bogie exchange. The SUW 2000 ATGCS requires a changeover track about 20 m long, with a shed if snow is around compared to a small marshalling yard required by bogie exchange.
An alternative to variable gauge axles and bogie exchange is axle exchange.