An Analysis of New Service Interchange Designs

An efficient freeway system will be essential to the
development of Africa, and interchanges are a key to that efficiency.
Around the world, many interchanges between freeways and surface
streets, called service interchanges, are of the diamond configuration,
and interchanges using roundabouts or loop ramps are also popular.
However, many diamond interchanges have serious operational
problems, interchanges with roundabouts fail at high demand levels,
and loops use lots of expensive land. Newer service interchange
designs provide other options. The most popular new interchange
design in the US at the moment is the double crossover diamond
(DCD), also known as the diverging diamond. The DCD has
enormous potential, but also has several significant limitations.
The objectives of this paper are to review new service interchange
options and to highlight some of the main features of those
alternatives. The paper tests four conventional and seven
unconventional designs using seven measures related to efficiency,
cost, and safety.
The results show that there is no superior design in all measures
investigated. The DCD is better than most designs tested on most
measures examined. However, the DCD was only superior to all
other designs for bridge width. The DCD performed relatively poorly
for capacity and for serving pedestrians. Based on the results, African
freeway designers are encouraged to investigate the full range of
alternatives that could work at the spot of interest. Diamonds and
DCDs have their niches, but some of the other designs investigated
could be optimum at some spots.

• Joseph E. Hummer

• Alternative
• design
• diverging diamond
• freeway
• interchange.

[1] Hughes, W., R. Jagannathan, D. Sengupta, and J. Hummer, Alternative
Intersections/ Interchanges: Informational Report, FHWA-HRT-09-060,
Washington, DC, April 2010.
[2] Chlewicki, G. L., "New Interchange and Intersection Designs: The
Synchronized Split-Phasing Intersection and the Diverging Diamond
Interchange," 2nd Urban Street Symposium, TRB, Anaheim, CA, 2003.
[3] Bared, J.G., P.K. Edara, and R. Jagannathan, "Design and Operational
Performance of Double Crossover Intersection and Diverging Diamond
Interchange," Transportation Research Record 1912, 2005.
[4] Edara, P. K., J. G. Bared, and R. Jagannathan, "Diverging Diamond
Interchange and Double Crossover Intersection - Vehicle and Pedestrian
Performance," 3rd International Symposium on Highway Geometric
Design, Chicago, IL, June 2005.
[5] FHWA, "Drivers' Evaluation of the Diverging Diamond Interchange,"
Tech Brief, FHWA-HRT-07-048, McLean, VA, 2007.
[6] "Diverging Diamond Interchange," brochure produced by the Missouri
Department of Transportation, Springfield District, 2008.
[7] Young, J. and N. English, "Diverging Diamond Interchange,"
presentation to the Ohio Transportation Engineering Conference
(OTEC), Columbus, 2007.
[8] Orchard, Hiltz, and McCliment, Inc., "Diverging Diamond Interchange,"
Livonia, MI, 2008.
[9] Aerial photos from www.bing.com.
[10] Asokan, et al., "Alternative Intersections Selection Tool-AIST," Paper
10-2146, presented at the 89th Annual Meeting of the TRB, Washington,
DC, 2009.
[11] Dorothy, P.W., T.L. Maleck, and K.K. Miller, "The Operational Aspects
of the Michigan Urban Diamond Interchange," Transportation Research
Record 1612, 1998.
[12] Reid, J.D., Unconventional Arterial Intersection Design, Management
and Operations Strategies, Parsons Brinckerhoff Quade and Douglas,
Inc., New York, NY, September 2003.
[13] Crawford, Murphy, and Tilly, Inc., "Interstate 55-MO Route 141
Corridor Study, Arnold, Missouri," Prepared for Missouri DOT, St.
Louis, March 22, 1999.