Dumbbell

For the at-grade intersection design analogous to dumbbell and dogbone interchanges, see Bowtie (road).

The ramp intersections may also be configured as a pair of roundabouts to create a type of diamond interchange often called a dumbbell interchange (due to its aerial resemblance to a dumbbell), and sometimes called a double roundabout interchange. Because roundabouts can generally handle traffic with fewer approach lanes than other intersection types, interchange construction costs can be reduced by eliminating the need for a wider bridge. This configuration allows other roads to form approach legs to the roundabouts and also allows easy U-turns.

• Staff (April 2010). “Chapter 9: Other Interchange Configurations”. Alternative Intersections/Interchanges: Informational Report (AIIR). Federal Highway Administration. FHWA-HRT-09-060. Retrieved October 8, 2012.
• Marshall, Chris (2012). “Interchanges: Dumbbell Interchange”. Chris’s British Road Directory. Self-published. Archived from the original on January 18, 2013. Retrieved February 25, 2013.
• Federal Highway Administration (FHWA): Manual on Uniform Traffic Control Devices (MUTCD), Edition 2009, Revision 2, May 2012], Figure 3C-14. Example of Markings for a Diamond Interchange with Two Circular-Shaped, Roundabout Ramp Terminals, p.412 (PDF p.452)
• “Double Roundabout Interchange: Design and Operations”. An Applied Technology and Traffic Analysis Program: Unconventional Arterial Intersection Design. University of Maryland, College Park / Maryland State Highway Administration. 2011. Archived from the original on December 24, 2013. Retrieved February 25, 2013.

This type of interchange is common in the United Kingdom and Ireland, and is becoming increasingly common in the United States. Examples of dumbbell interchanges in the United States are located on Interstate 35 in Medford, Minnesota, on Interstate 87 in Malta, New York, on Interstate 17 at Happy Valley Road north of Phoenix, Arizona, and on Interstate 80 at California State Route 89 (exit 185) in Truckee, California. An example in Canada is found on the Pat Bay Highway in North Saanich, British Columbia, near Victoria International Airport.

One or both roundabouts in the dumbbell interchange may also contain side lanes to increase the capacity. A good example of such a “turbo” dumbbell interchange, which was formerly a half cloverleaf, can be seen in Jülich, Germany at 50.914055°N 6.323368°E.

There are interchanges similar to dumbbells in which the ramps do not meet the roundabouts at intersections; these more closely resemble bowtie intersections. One such interchange exists at the junction between the Ruta Interbalnearia and Route 35 North near La Floresta, Uruguay (34.7495°S 55.6775°W).

Dogbone

A variation of the dumbbell interchange, often called a dogbone interchange (due to its aerial resemblance to a real or toy dog bone), and sometimes also called a double roundabout interchange, occurs when the roundabouts do not form a complete circle but instead have a “raindrop” or “teardrop” shape. These two raindrop roundabouts are fused together, forming a single “squashed” roundabout.

• Staff (April 2010). “Chapter 9: Other Interchange Configurations”. Alternative Intersections/Interchanges: Informational Report (AIIR). Federal Highway Administration. FHWA-HRT-09-060. Retrieved October 8, 2012.

This configuration reduces conflicts between vehicles entering the raindrop roundabouts from the ramps, reducing queueing and delays, compared with the dumbbell interchange. Direct U-turns are not possible, although the movement can be made by circulating around both raindrop roundabouts. An example of a dogbone interchange in the United States is located on Interstate 70 in Avon, Colorado, United States; more compact examples, which show less of the characteristic “dog bone” shape, are located along Keystone Parkway in Carmel, Indiana, United States. Several interchanges similar to those along Keystone Parkway are being built along the new US 31 freeway under construction in northern Indiana.

• “Double Roundabout Interchange: Design and Operations”. An Applied Technology and Traffic Analysis Program: Unconventional Arterial Intersection Design. University of Maryland, College Park / Maryland State Highway Administration. 2011. Archived from the original on December 24, 2013. Retrieved February 25, 2013.
• Google. “Teardrop roundabout in Avon, CO” (Map). Google Maps. Google.
• “The New US 31 Hamilton County: Frequently Asked Questions”. Hamilton County, Indiana. March 2015. Retrieved December 3, 2015.

There are some hybrid interchanges of dumbbell and dogbone having one raindrop and one full roundabout. This is made when the roundabout intersects more roads than the cross street and ramps. Some examples are at exit 38 of the N7 road in Groningen, Netherlands (at 53.21462°N 6.602509°E); and Ennis Avenue (National Route 1) at Safety Bay Road (State Route 18 / Tourist Drive 202) on the border of the suburbs of Waikiki and Warnbro in the City of Rockingham, Western Australia (at 32.32486°S 115.76704°E).

A tennis ball interchange resembles a dogbone interchange, with the difference being that right turning movements (in a country where traffic drives on the left) cut through the roundabouts like a regular diamond interchange instead of going around the roundabout. Such a design is found in Perth, Western Australia, between Roe Highway (State Route 3) and Berkshire Road (at 31.96945°S 116.00107°E).

• “Roe Highway / Berkshire Road Interchange” (PDF). Gateway WA. Gateway WA. April 2015. Archived (PDF) from the original on September 26, 2015. Retrieved September 26, 2015

See also

• Roads portal

References

1. Staff (April 2010). “Chapter 9: Other Interchange Configurations”. Alternative Intersections/Interchanges: Informational Report (AIIR). Federal Highway Administration. FHWA-HRT-09-060. Retrieved October 8, 2012.
2. Marshall, Chris (2012). “Interchanges: Dumbbell Interchange”. Chris’s British Road Directory. Self-published. Archived from the original on January 18, 2013. Retrieved February 25, 2013.
3. Federal Highway Administration (FHWA): Manual on Uniform Traffic Control Devices (MUTCD), Edition 2009, Revision 2, May 2012], Figure 3C-14. Example of Markings for a Diamond Interchange with Two Circular-Shaped, Roundabout Ramp Terminals, p.412 (PDF p.452)
4. “Double Roundabout Interchange: Design and Operations”. An Applied Technology and Traffic Analysis Program: Unconventional Arterial Intersection Design. University of Maryland, College Park / Maryland State Highway Administration. 2011. Archived from the original on December 24, 2013. Retrieved February 25, 2013.
5. Google. “Teardrop roundabout in Avon, CO” (Map). Google Maps. Google.
6. “The New US 31 Hamilton County: Frequently Asked Questions”. Hamilton County, Indiana. March 2015. Retrieved December 3, 2015.
7. “Roe Highway / Berkshire Road Interchange” (PDF). Gateway WA. Gateway WA. April 2015. Archived (PDF) from the original on September 26, 2015. Retrieved September 26, 2015.