From Roader's Digest: The SABRE Wiki
|The M1 between junctions 7 and 8 has CD lanes|
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CD stands for Collector/Distributor Lane, which despite the name, is a separate carriageway alongside the main route intended to separate traffic wishing to continue along a route from traffic wishing to enter or exit, preventing a phenomenon known as weaving. Typically these are used on congested lengths of road with multiple interchanges in quick succession.
Where an additional lane is used as part of the main carriageway between two junctions, this is known as an auxiliary lane. These are typically divided from the through lanes by different road markings, for instance on the M4 between Junctions 43 and 44.