Partial cloverleaf interchange

A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The parclo interchange was invented by the Ministry of Transportation of Ontario 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 ahead of the arterial road, while B designates that two ramps meet the freeway beyond 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).

The parclo A2 and B2 are commonly used on rural freeways such as Highway 402 and Highway 416, where the ramps can be added without widening the street overpass/underpass to include deceleration lanes (normally needed on the A4 in order to safely enter the loop ramps that lead to the freeway). The parclo A2 and B2 ramps are also usually longer and allow for higher speeds than their A4 counterparts because of rural land availability. It is possible to upgrade an A2 to an A4 by adding directional ramps, serving arterial-to-freeway traffic that would otherwise be forced to make a left turn to enter the loop ramps.

This page was last edited on 22 April 2018, at 02:08 (UTC).
Reference: under CC BY-SA license.

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