Source: AASHTO. 2018. A policy on geometric design of highways and streets, seventh edition. Washington, DC: AASHTO. Note: SPUI (Single-Point Urban Interchange).
The setting of highway networks necessitated interchanges where two highways intersect. The grade separation of interchanges allows continuous traffic without interruptions such as stops or traffic lights, increasing capacity. There is a wide variety of interchange designs, with the most common including:
- Trumpet interchange. Allows one highway to end/begin perpendicularly to another highway with the construction of one overpass.
- Three-way interchange. Also called T interchange and allows one highway to end/begin perpendicularly to another highway. It has a lower footprint than a trumpet interchange but requires the construction of three overpasses.
- Single quadrant interchange. Allows two highways to connect without interrupting traffic at the intersection (which can be an overpass), but requires two traffic lights, creating an interruption.
- Diamond interchange. Between a highway and interrupted traffic road, implying that it is a service interchange. It usually has four ramps accessing the highway and intersecting the interrupted traffic road, which is commonly an overpass.
- Single-point urban interchange (SPUI). A service interchange acting in a similar fashion to a diamond interchange, but where the ramps converge at a single intersection. It has a lower footprint than a diamond interchange but requires a wider overpass.
- Cloverleaf interchange. A four-way two-level interchange where each turn is handled by a single ramp. They have a significant footprint and are common points of congestion because of traffic weaving as traffic exiting a ramp interacts over a short distance with traffic entering a ramp.
- Partial cloverleaf interchange. A simplification of the cloverleaf interchange design, but with fewer turn options and a lower footprint. A traffic light is often necessary for one highway.
- Stack interchange. A four-way four-level interchange that allows intersecting and overpassing ramps in all directions. It has a lower footprint than the cloverleaf interchange but is more expensive to build and maintain.