An <b>exclusive zone</b> is a track section which can be occupied by only one train at a time. Exclusive zones are marked with a blue band in the middle of ties. By default, every bi-directional track starts as an exclusive zone.
There are cases where the default exclusion zone on bi-directional track is not desired. For example, when connecting a double-track main line to a multi-track terminus station. In this case, it is common to first converge the main line (1) to a bi-directional track (2) and then split it to terminus stations (3). The bi-directional segment between the main line and stations (2) should not be exclusive, otherwise it would form, together with all lanes of the station, one exclusive zone and no more than one train could use the station.
When removing an exclusive zone from bi-directional tracks, <b>always replace it with a no-stopping zone</b>. Having a naked bi-directional track without exclusive and no-stopping zones will almost certainly result in trains blocked head-to-head.
An example where an explicit exclusive zone can be advantageous is a train staging area (sometimes called a buffer) where only one train should use each lane. Without an exclusive zone, two shorter trains may fit to one buffer lane which may not be desired in some cases.