One-person operation (OPO), also known as driver-only operation (DOO), one-man operation (OMO), single person train operation (SPTO), or one-person train operation (OPTO), similarly to driver-controlled operation, is operation of a train, bus, or tram by the driver alone, without a conductor.

On one-person operated passenger trains, the driver must be able to see the whole train to make sure that all the doors are safe for departure. On curved platforms a CCTV system, mirror or station dispatch staff are required.

Although extra infrastructure such as cameras and mirrors might require additional investment, one-person operation is usually faster and cheaper to implement than automatic train operation, requiring a smaller investment in, for example, platform intruder detection systems and track protection (fencing, bridge-caging, CCTV etc.). In some cases, one-person operation can be seen as an intermediate step towards automatic train operation.

While European freight trains are normally one-person operated, the larger North American freight trains are almost exclusively crewed by a conductor as well as the driver (commonly known in North America as the engineer).

While one-person operation is popular and on the rise among the train operating companies as it reduces the number of crew required and correspondingly reduces costs, it is for that reason controversial and is often strongly opposed by trade unions, arguing that it is an unsafe practice.

One of the first examples of a public transport vehicle that was developed specifically for one-person operation is the Birney streetcar introduced in the United States in 1916. The Birney was pre-equipped with one of the most important safety devices for enabling one-person operation – the dead man's switch. At the time (and to a certain extent also today) one of the most cited arguments against one-person operation was the safety risks to passengers and bystanders if the operator fell ill. The dead man switch ensured that the tram would stop in the event of an incapacitated driver. For this reason, the Birneys were also called "safety cars". Another critical feature of the Birney in dealing with safety issues from the critics of one-person operation was its compact size which eased the driver's view of the road and reducing the number of doors to a single one.

In the US, regardless of various technological solutions to resolve the safety issues of one-person operation, there was consistent resistance towards one-person operation among the drivers and conductors of the streetcars. Whenever the workforce was well-organized in unions – which was the case in around half of all cities with streetcar companies – any proposal of one-person operation would generally be challenged, regardless of whether the streetcar company was in serious financial difficulties. In many cities, it took a municipal ordinance to authorize one-person operation, thus also politicizing the subject. The result of all this was typically strikes and other industrial action whenever one-person operation was implemented.

While the Birney was one of the first public transport vehicles designed for one-person operation, it was not the first public transport vehicle to be equipped with a dead man's switch. In 1903, the Metropolitan District Railway equipped two of its A Stock trains with a dead man's switch. The switch was introduced so that one person could operate in the driving cab on their own, which became standard for all train companies operating the London Underground in 1908. Even though this did not make the trains one-person operated – seeing as the trains were still operated with a guard – it was one of the first steps towards it.