A three-level diamond interchange is a type of highway interchange where through traffic on both main roads is grade-separated from intersections which handle transferring traffic.[1] It is similar in design to a three-level stacked roundabout except for its use of (usually signalled) conventional intersections, and can be thought of as two diamond interchanges fused together.
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In a three-level diamond interchange, the two main roads are on separate levels, and on a third level, usually in the middle, there is a square of one-way roads. The square circulates clockwise where traffic drives on the left, or anticlockwise where it drives on the right. At each corner of the square is the terminal of an exit ramp from one main road and an entrance ramp to the other main road. Traffic transferring from one road to the other to make an overall right turn only passes through one corner of the square, at which point a right turn is made. Transfer traffic making an overall left turn must proceed straight through the first intersection it encounters, turn left at the next, and then proceed straight through a third intersection to enter the other main roadway.
Three-level diamond interchanges are most common in urban settings where the right-of-way for a new interchange must be kept to a minimum.
| Location | First Route | Second Route | Notes |
|---|---|---|---|
| Cedar Rapids, Iowa | I-380 | IA 100 | Collector/distributor roads intersect. |
| Sioux City, Iowa | I-29 | US 77 | |
| Detroit, Michigan | I-75 (Walter P. Chrysler Freeway) | M-102 (8-Mile Road) | I-75 uses frontage roads. |
| Detroit, Michigan | M-102 (8-Mile Road) | M-1 (Woodward Avenue) | |
| Detroit, Michigan | M-102 (8-Mile Road) | M-10 (John C. Lodge Freeway) | Includes flyovers from northbound M-10 to westbound M-102, eastbound M-102 to southbound M-10, and westbound M-102 to northbound M-10. M-10 uses frontage roads. |
| Redford Township, Michigan | I-96 | US 24 (Telegraph Road) | |
| Jefferson City, Missouri | US 50/US 63 northbound | US 54/US 63 southbound | A flyover ramp allows southbound US 63 traffic to join US 50 east, bypassing one intersection. The ramp from east 50/north 63 to west 54 is closed and motorists must use a nearby city street to make a such maneuver. |
| Asheville, North Carolina | I-240 | US 70 | I-240 Exit 7 |
| Marple Township, Pennsylvania | I-476 | US 1 | I-476 Exit 5 |
| Robinson Township (Washington County), Pennsylvania | Toll PA 576 PA 576 | US 22 | PA 576 Exit 6; partially completed, temporary terminus of PA 576 |
| South Strabane Township, Pennsylvania | I-79 | Pike Street/Locust Avenue | I-79 Exit 40 "Meadow Lands"; under construction, to open fully in 2012 |
| Alexandria, Virginia | I-395 Shirley Highway | Seminary Road | I-395 Exit 4 |
| Fairfax County, Virginia | Fairfax County Parkway | US 29 | The south end of West Ox Road also meets this interchange. |
| Welch, West Virginia | US 52 (King Coal Highway) | US 121 (Coalfields Expressway) | As of 2011, grading has been completed for interchange but interchange itself has not been constructed. |
| Wheeling, West Virginia | I-470 | US 250 / WV 2 | Entire interchange is elevated above city streets. |
| Wauwatosa, Wisconsin | US 45 | WI 190 (Capitol Drive) | An access road for the adjacent Harley-Davidson plant is also part of the interchange. |
A few examples of this can also be found in Texas; however, the interchanges usually include the frontage roads as well. If the traffic amounts increase the interchange is usually converted into a stack interchange.
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