as folded diamonds, due to their similarity with diamond interchanges. Sometimes the ramps in a folded diamond are actually local streets; surface roads upgraded to higher standards often do this to save money on land acquisition. This type of interchange long predates the parclo; the Merritt Parkway and Queen Elizabeth Way, both built in the 1930s, used mainly folded diamonds and cloverleaves. Another example of this is Highway 401's interchange with Highway 2 east of Tilbury (Exit 63): the ramps also have intersections fairly close to the freeway to allow traffic to continue on a rural country road (Jeannette's Creek Road / McKinlay Road) which formerly met Highway 2. Depending on traffic and land needs, hybrid designs, such as the parclo AB and parclo A3, can be created. A notable example of a parclo AB interchange includes the Highway 417 and the Woodroffe Avenue interchange in Ottawa. Other variants, not describable using Ontario's system, eliminate one or more outside ramps, while leaving the loop ramps in those quadrants. In the United States, folded diamonds are frequently used in interchanges with roads that have a railroad line closely paralleling the surface street; entrance/exit ramps are not permitted to have level crossings in modern American practice. Implementation In California, Caltrans currently has a policy that whenever cloverleaf interchanges between freeways and surface streets are being rebuilt, they are turned into parclo interchanges by removing some of the loop ramps (or in rare cases bridges will be added between adjacent loop ramps—see cloverleaf interchange for details). Various forms of parclo interchanges are used on the North Luzon Expressway in the Philippines. The configuration of parclo interchanges (particularly those of the "folded diamond" type) allows for the consolidation of toll barriers at points where onramps and offramps run alongside each other. A single large barrier can serve each onramp/offramp pair simultaneously, reducing construction and operation expenses at through junctions. When possible, such as at terminal junctions, trumpet interchanges are preferred since they only require one large toll barrier for all four on/off-ramps. References Road interchanges Roads in Ontario Canadian inventions