Single-point urban interchange

The design was created in order to help move large volumes of traffic through limited amounts of space efficiently.

[3][neutrality is disputed] Sometimes a SPUI will allow traffic to proceed straight through from the offramp to the onramp; this usually happens when the ramps connect with frontage roads.

The most commonly cited advantages of SPUIs are improved operation efficiency and safety as well as reduced right-of-way requirements compared to other interchange forms.

SPUIs also allow for wider turns, easing movement for large vehicles, such as trucks and RVs.

[6] The major disadvantage of SPUIs over other types of road junctions is the increased cost due to the need for a longer or wider bridge.

A freeway-under SPUI (as in the upper diagram) requires a wider bridge over the free-flowing road to make room for the compressed on- and offramps.

[citation needed] Due to the large intersection area, the traffic lights need a longer yellow and red phase to clear the intersection, and, even then, it may not be long enough for a bicyclist entering on green or yellow to make it across before opposing traffic gets a green.

The large area in which lanes cross may have to be shut down to allow efficient and thorough cleaning lest a snowplow leave piles of snow, interfering with traffic and visibility in the middle of the uncontrolled pavement.

Other interchange types designed for efficiency, such as the six-ramp partial cloverleaf and the diverging diamond, require just two signal phases.

It was designed by Wallace Hawkes, Director of Transportation Engineering at J. E. Greiner Company (later URS Corporation), who has been called the "granddaddy of the urban interchange".

Smaller versions of the SPUI can also be found on non-autobahn roads in German cities, with right-turning traffic under signal control, located in Heilbronn, Karlsruhe, Sindelfingen, Stuttgart, and Wiesbaden.

There is one such interchange in Pultney Township, Belmont County, Ohio, between State Route 7 (SR 7) and Interstate 470 (I-470) at 40°02′52″N 80°44′01″W / 40.047657°N 80.733542°W / 40.047657; -80.733542.

SR 7's left on- and offramps run between its carriageways, meeting the I-470 ramps at an at-grade intersection.

Schematic of a freeway-under SPUI where traffic drives on the right . Traffic entering the freeway is in red. Traffic exiting the freeway is in green. Through traffic is in gray. All traffic motion of the same color can proceed simultaneously.
A typical freeway-over SPUI. This example, near Orlando , has since been demolished.
California State Route 87 at Taylor Street, a freeway-under SPUI
Inverted SPUI where traffic drives on the right . Ramps are located between carriageways .
Offset SPUI