The Superiority of Diamond Interchanges vs. Cloverleaf Interchanges
Lisa Jo MacEwen
Interchanges control access and handle the movement of traffic between roadways. In this paper only 2 types of interchanges are studied: the diamond interchange and the cloverleaf interchange. The diamond interchange is a system of interconnecting roadways that provides for the movement of traffic between two or more highways on different levels, usually signalized to control conflict points. A cloverleaf interchange is a two-level interchange in which left turns are handled by loop roads, which creates a free-flow traffic pattern where traffic signals would cause congestion. There are considerably less points of conflict in a diamond interchange than there are for cloverleaf interchanges mainly because of the weaving sections. Considering safety alone, the diamond interchange is preferable to a cloverleaf interchange.
Interchanges are essential to freeway operation. They control access and handle the movement of traffic between roadways. Unfortunately, interchanges are inferior in design to the freeways and contribute to collisions. Interchanges cause collisions because of the likelihood of increased speed differentials between the freeway mainlines, ramp junctions, and ramps. Interchanges can also be attributed to accidents because vehicles need to change lanes in a limited area in and around interchanges in order to merge and diverge. Often, more than one lane change can occur in a very short time.
The diamond interchange is an important facility for managing traffic demands in urban areas. Although there is a similarity with closely spaced intersections in schematic form, the diamond interchange often has a unique control strategy and operational characteristics. The diamond interchange is a system of interconnecting roadways that provides for the
References: Bared, J., Powell, A., Kaisar, E., Jagannathan, R. (2005). ‘Crash Comparison of Single Point and Tight Diamond Interchanges.’ Journal of Transportation Engineering, 131(5), 379-381. doi:10.1061/(ASCE)0733-947X(2005)131:5(379). Golob, Thomas F., Recker, Wilfred W., Alvarez, Veronica M. (2004) ‘Safety aspects of freeway weaving sections’. Transportation Research Part A. 38: 35-51. Lee, S., Messer, C., Keechoo, C. (2006). ‘Actuated Signal Operations of Congested Diamond Interchanges.’ Journal of Transportation Engineering, 132(10), 790-799. doi:10.1061/(ASCE)0733-947X(2006)132:10(790). Moon, Jae-Pil and Hummer, Joseph E.(2009) ‘Development of Safety Prediction Models for Influence Areas of Ramps in Freeways’, Journal of Transportation Safety & Security, 1: 1, 1 — 17 Sangsoo, L., Messer, C., Youngtae, O., Choulki, L. (2004). ‘Assessment of Three Simulation Models for Diamond Interchange Analysis.’ Journal of Transportation Engineering, 130(3), 304-312. doi:10.1061/(ASCE)0733-947X(2004)130:3(304). Xu, Y., Zhu, S., Wang, H., Guan, J., Sun, Q., Liu, B., Liu, D., Xia, J., Antoniou, C. (2008). ‘Relationship between Weaving Length and Traffic Safety in Road Interchanges.’ Transportation and Development Innovative Best Practices 2008. ASCE: Chicago, 2008. 240-245.