Free-flow interchange
Encyclopedia
A free-flow interchange is an interchange
in which all roads are grade-separated
, 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 roundabout
s). Free-flow interchanges are less likely to induce traffic congestion
than non-free-flow, but are typically more expensive both in money and in land.
Some free-flow interchange bring additional problems such as weaving or outside lane (passing lane) exits that may be necessary to avoid additional costs, but lead to congestion and accidents and ultimately to an upgrade to another type of interchange. Interchanges involving roundabouts are listed as non-free-flow because drivers entering a roundabout have to slow down considerably possibly creating backups.
Interchange (road)
In the field of road transport, an interchange is a road junction that typically uses grade separation, and one or more ramps, to permit traffic on at least one highway to pass through the junction without directly crossing any other traffic stream. It differs from a standard intersection, at which...
in which all roads are grade-separated
Grade separation
Grade separation is the method of aligning a junction of two or more transport axes at different heights so that they will not disrupt the traffic flow on other transit routes when they cross each other. The composition of such transport axes does not have to be uniform; it can consist of a...
, 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 roundabout
Roundabout
A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...
s). Free-flow interchanges are less likely to induce traffic congestion
Traffic congestion
Traffic congestion is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, and increased vehicular queueing. The most common example is the physical use of roads by vehicles. When traffic demand is great enough that the interaction...
than non-free-flow, but are typically more expensive both in money and in land.
Some free-flow interchange bring additional problems such as weaving or outside lane (passing lane) exits that may be necessary to avoid additional costs, but lead to congestion and accidents and ultimately to an upgrade to another type of interchange. Interchanges involving roundabouts are listed as non-free-flow because drivers entering a roundabout have to slow down considerably possibly creating backups.
Examples of free-flow interchanges
- Stack interchangeStack interchangeA stack interchange is a free-flowing grade separated junction between two roads.In countries where one drives on the right, left turns are handled by semi-directional flyover/under ramps...
- Cloverleaf interchangeCloverleaf interchangeA cloverleaf interchange is a two-level interchange in which left turns, reverse direction in left-driving regions, are handled by ramp roads...
- Trumpet interchange
- Cloverstack interchange
- Directional T
- Semi-directional T
- Turbine (whirlpool) interchange
Examples of interchanges that are not free-flow
- Diamond interchangeDiamond interchangeA diamond interchange is a common type of road junction, used where a freeway crosses a minor road. The freeway itself is grade-separated from the minor road, one crossing the other over a bridge...
- Parclo interchangeParclo interchangeA partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The parclo interchange was developed by the Ontario Ministry of Transportation as a replacement for the cloverleaf on 400-Series Highways, removing the dangerous weaving patterns and allowing for more...
- Roundabout interchangeRoundabout interchangeA roundabout interchange is a type of interchange between a controlled access highway such as a motorway or freeway, and a minor road, in which the slip roads to and from the motorway carriageways converge at a single roundabout, which is grade-separated from the motorway lanes with bridges...
- Three-level diamond interchange
- Three-level stacked roundabout