A free-flow interchange is an interchange in which all roads are

grade-separated In civil engineering (more specifically highway engineering), grade separation is a method of aligning a junction of two or more surface transport axes at different heights ( grades) so that they will not disrupt the traffic flow on other tr ...

, and where movement from one road to another does not require the driver to stop for traffic (for example, the interchange may not include traffic lights or unsignalized

at-grade intersection An intersection or an at-grade junction is a junction where two or more roads converge, diverge, meet or cross at the same height, as opposed to an interchange, which uses bridges or tunnels to separate different roads. Major intersections ar ...

s). Free-flow interchanges are less likely to induce

traffic congestion Traffic congestion is a condition in transport that is characterized by slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion on urban road networks has increased substantially since the 1950s, resulting in m ...

than non-free-flow, but are typically more expensive both in money and in land. Some free-flow interchanges bring additional problems such as weaving or passing lane/fast lane exits (i.e. left exits in areas with right-hand traffic, and vice versa) that may be necessary to avoid additional costs, but lead to congestion and accidents and ultimately to an upgrade to another type of interchange. A free flow interchange design called double crossover merging interchange (DCMI) has received a patent."United States Patent 8,950,970: Double Crossover Merging Interchange". United States Patent and Trademark Office. February 10, 2015. Retrieved August 4, 2015. The DCMI includes elements from the diverging diamond interchange (DDI) and the standard

diamond interchange A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road. Design The freeway itself is grade separation, grade-separated from the minor road, one crossing the other over a bridge. ...

. It eliminates the disadvantages of weaving and of merging into the outside lane from which the standard DDI variation suffers.

Examples of free-flow interchanges

* Stack interchange *

Cloverleaf interchange A cloverleaf interchange is a two-level interchange (road), interchange in which all turns are handled by slip roads. To go left (in right-hand traffic; reverse directions in left-driving regions), vehicles first continue as one road passe ...

Trumpet interchange In the field of road transport, an interchange (American English) or a grade-separated junction (British English) is a road junction that uses grade separations to allow for the movement of traffic between two or more roadways or highways, usi ...

* Cloverstack interchange * Directional T * Semi-directional T * Turbine (whirlpool) interchange

Examples of interchanges that are not free-flow

Diamond interchange A diamond interchange is a common type of road junction, used where a controlled-access highway crosses a minor road. Design The freeway itself is grade separation, grade-separated from the minor road, one crossing the other over a bridge. ...

Partial cloverleaf interchange A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The design has been well received, and has since become one of the most popular freeway-to-arterial interchange designs in North America. It has also bee ...

* Three-level diamond interchange * Diverging diamond interchange

References

{{Road junction types Road interchanges da:Motorvejskryds de:Autobahnkreuz sv:Motorvägskorsning