Blocks are sections of track that are defined by their geographical features. A block may be between two stations, between a station and a turnout, between two turnouts, etc. Blocks are usually protected by signals to enter and to exit the block. This is called block signalling or in some cases, absolute blocks.

Whilst very common, block signalling has the diadvantage that all trains must adhere to one-size-fits-all rules and to worst-case-scenarios method of signalling. For example, block signals must be placed for the faster/heavier trains to allow for their large braking distances, even though some trains could slash this requirement.