Folded diamond interchange

A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The parclo interchange was invented by the Ontario Ministry of Transportation as a replacement for the cloverleaf on 400-Series Highways where full grade separation is not required, removing the dangerous weaving patterns and allowing for more acceleration and deceleration space on the freeway.

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 been used occasionally in some European countries, such as Germany, Croatia, Italy, the Netherlands, and the United Kingdom.

In Ontario, the specific variation is identified by a letter/number suffix after the name. Other jurisdictions do not have naming conventions, so Ontario's naming conventions are used in this article. The letter A designates that two ramps meet the freeway before the driver crosses the arterial road, while B designates that two ramps meet the freeway past the crossing.

The number designates how many quadrants of the interchange contain ramps. In left-hand drive countries, the ramps function the same as in right-hand drive countries, but ramps with the same designation appear visually reversed. Common parclo configurations include the Parclo A2, Parclo B2 and Parclo A4.

Parclo A2 and B2 configurations contain four ramps. On each side of the freeway there is a loop ramp and a directional ramp. In Parclo A2, the loop ramps serve as on-ramps and the directional ramps serve as off-ramps. In Parclo B2 the roles are reversed. Both on- and off-ramps require controlled intersections at the arterial road (sometimes loop and directional ramps from the same side of the freeway will utilize the same intersection).

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