
An example of a C/D road, on the top side of the freeway.

An example of a more sophisticated C/D road setup; exiting traffic passes over entering traffic.
A 'collector/distributor road', often abbreviated as 'C/D road', is a one-way road next to a
freeway that is used for some or all of the ramps that would otherwise merge into or split from the main lanes of the freeway. It is similar to a
frontage road, and related to the more complex
Express-collector systems used in many large cities, but is built to freeway standards. It is used to eliminate or move weaving from the main lanes of the freeway, particularly at
Cloverleaf Interchanges.
In the simplest form, all ramps that would normally touch the freeway are instead shifted outwards to the C/D road. There is still weaving, but it is no longer on the main lanes. More sophisticated designs take some ramps over or under the C/D road, often eliminating
weaving entirely.
See also
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Cloverleaf interchange
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Frontage road
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Local-express lanes
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Hierarchy of roads
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The Basketweave