Interchanges

Interchanges are a type of road junction designed to allow traffic to transfer between two or more roads without stopping at cross traffic. They are typically grade-separated, using bridges or tunnels to keep traffic streams apart and provide access via ramps. Interchanges are used where high traffic volumes, high speeds, or safety concerns make at-grade intersections impractical.

Key components of interchanges include mainlines for through traffic, on-ramps and off-ramps for entering and exiting, flyovers or underpasses to separate flows, and often collector-distributor roads and acceleration or deceleration lanes. Ramps may include weaving sections where drivers must merge with or diverge from other traffic. The design aims to minimize conflict points and maintain smooth, continuous movement.

Common types of interchanges vary in layout and scale. Cloverleaf interchanges use looping ramps to accommodate all turning movements but require substantial land area and can create weaving problems. Diamond interchanges are compact and common where a freeway intersects a lower-speed road, sometimes with signals on ramp approaches. Partial cloverleafs, stack interchanges, turbine interchanges, and trumpet interchanges represent higher-capacity or more space-efficient options for growing traffic. Roundabout interchanges combine circular junctions with ramp connections and are used in some regional networks.

Design considerations encompass traffic volumes, speeds, demand patterns, sight distances, and vehicle weaving, as well as construction costs, land availability, and environmental impact. Interchanges improve safety by avoiding at-grade collisions and increase efficiency by separating conflicting movements, but they can be expensive and, in some configurations, create ramp-related safety or congestion challenges.

Overall, interchanges play a central role in modern road networks, balancing capacity, safety, and cost to facilitate efficient long-distance and urban traffic movement.