The line is identified as M4. You can find this designation on metro maps, signs in passageways, platform information boards, and transport apps. Before boarding, always check not only the line number or colour, but also the final destination of the train — this will help you avoid boarding a service heading in the wrong direction.

This metro line runs through Sofia (Bulgaria). Metro lines typically connect several parts of the city — from residential neighbourhoods to business districts and the city centre. To find out whether this line suits your journey, open the metro map and check the station locations relative to your destination. Sometimes one transfer is more convenient than searching for a direct route.

The line is operated by Метрополитен. This organisation is responsible for train services, station condition, safety, and infrastructure. If you encounter any issues — delays, technical problems, or ticketing queries — please contact the operator directly. Providing your station, direction of travel, and the time of your journey will help them handle your enquiry more quickly.

This line is part of the «Градски транспорт София» network. Within a single transport network, the same fare rules, ticketing, and transfer policies typically apply. This means one ticket or travel card may be valid across multiple lines in the network without requiring an additional payment when changing trains.

On metro maps, this line is shown in yellow. Colour coding is the primary navigation aid in metro systems — it helps you quickly identify the right direction on signs, maps, and information boards. When making transfers, always pay attention to the line colour to avoid confusing platforms or directions.