The diverging diamond interchange is quickly gaining popularity in the U.S. Busy localities are beginning to see the need for diverging diamond interchange (DDI) to improve traffic flow. DDIs improve safety by eliminating the left turns, and limiting the number of phases in traffic signals in comparison to normal diamond interchange (Anderson et al., 2012). Florida’s first DDI is under construction at one of the busiest stretches in Florida. The innovative design of a DDI makes it economically effective; it will ease congestion, improve operational efficiency and reduce deadly crashes at I-75 and University Parkway.
Anderson et al. (2012) notes that a DDI is quite different from the conventional diamond interchange. Conventional diamond interchanges are quite confusing for drivers, and they have become accident hot spots across the country. However, the design of the DDI reduces accidents at the interchange by at least 50%. According to Morris (2016), the idea of a DDI was introduced in the U.S. in 2000 by a graduate student: Gilbert Chlewicki. Chlewicki came up with the idea to ease accidents at diamond interchanges by introducing the concept of diverging diamond interchange for his master’s program in transportation engineering, and the idea was experimented in Springfield, Missouri in 2009 (Morris, 2016). DDI was a success in Missouri, and it was associated with over 60% reduction in crash rate. After the success of Missouri’s DDI, a number of cities are in the process of building DDIs, but Sarasota’s DDI is the largest so far. The busy interchange in Sarasota has been facing major congestion and crash challenges due to the continuous growth in Lakewood Ranch to the east, and the newly growing Regatta Park.
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Edara et al. (2015) conducted a research on Missouri’s DDI using different types of before-after evaluation to judge whether it reduced crashes. The study showed that DDI significantly reduced the rate of severe crashes, and eliminated ramp terminal-related crashes to the left angle. The significant reduction in road crashes forms the major benefit of Sarasota’s DDI. Road crashes in the U.S. cost the government a lot of money, and they are quite costly for overpopulated states such as Florida. According to Blincoe et al. (2010) 32,999 people were killed in traffic accidents, 3.9 million people were injured and 24 million vehicles were damaged, eventually, the total costs of traffic accidents in 2010 was $242 billion. The economic costs of traffic accidents extend beyond the damaged vehicle and related injuries. Accidents lead to lower productivity, legal cases, and property damage among other costs. A simple road accident has a domino effect, which could be avoided with better designs of roads as seen in Sarasota’s DDI’s.
According to Edara et al. (2015) there are three benefits of DDIs that impact on the economy of the city. First, DDIs contribute to operational efficiency. DDIs are associated with lower overall delays. The design of the DDI ensures that the traffic flows seamlessly at the interchange. Just like a diamond interchange, a DDI has two ramp terminals, but DDIs have a different crossing intersection such that at the interchange motorists drive at the “wrong directions.” Eventually, drivers do not have to turn left, reducing any form of contact with drivers from the opposite direction that could result in a collision. In Sarasota interchange, drivers will travel on University Parkway through a crossover onto the left side of the road. The operational efficiency fostered by DDIs reduces traffic congestion in the city such that city residents will get to work and their businesses easily.
DDIs are associated with fewer conflict points in comparison to conventional diamond interchanges. Edara et al. (2015) notes that DDI in Springfield has 18 conflict points in comparison to a normal diamond interchange that has 30 conflict points. A DDI conflict points involve 2 crossing points, 8 merging, and 8 diverging. The 30 conflict points in a diamond interchange are 10 crossing points, 10 merging, and 10 diverging points. DDI reduces 8 crossing points, hence reduces exposure to traffic accidents.
Another positive economic effect of DDIs is that they have lower costs of retrofitting into an existing diamond interchange. DDIs and normal diamond interchanges have a lot of structural similarities, hence it is easy to upgrade already existing diamond interchange to a DDI.
However, Sarasota’s DDI will be the largest in the country. While its construction is motivated by the need to reduce accidents and improve its operation, it is a very costly project. Sarasota’s DDI costs $74.5 million (Le Coz, 2016). This is an extensive project that will be completed in September 2017. It involves improvement on –75 bridges at Errie Creek and Foley Creek. The on-ramps and off-ramps at the interchange have to be realigned, drainage and lighting also have to be improved. Roads have to be widened, while other new bridges have to be constructed. Constructing the DDI is quite costly to the city, especially since it involves a lot of money and takes a longer period of time to be completed.
Sarasota’s DDI construction is taking a lot of time, and disruptions of normal activities has occurred in the process. Motorists using that particular road have endured detours and delays as the construction tasks are underway (Le Coz, 2016). Once the DDI is complete, the possibility of wrong crashes is still possible. A study on the Springfield DDI’s showed that 4.8% of fatal and injury crashes were caused by wrong way incidents (Edara et al., 2015). This is a small price to pay in exchange for high severity accidents in conventional diamonds, and most wrong-turn incidents in the DDI lead to length detours rather than accidents. It is worth noting that DDIs are not applicable in all situations, hence they must be constructed in strategic locations that will foster easy traffic flow (Anderson et al., 2012).
Regardless of the high costs of construction and the disruptions caused, Sarasota’s DDI will eliminate ramp terminal accidents because of its crossover design. The diverging interchange shifts directions in the opposite sides of the road creating smoother left turns and smooth traffic flow that eventually directs the traffic into their respective sides of the road.
In conclusion, Springfield’s DDI was used as an experiment for the effectiveness of DDI’s. While DDIs are not advisable for all locations, I-75 and University Parkway make the perfect location for a DDI. Nonetheless, Sarasota’s DDI is much larger than Springfield’s DDI, therefore, it is important to experiment different simulation models that will be used to control the DDI effectively to ensure operational effectiveness and reduced crashes.
References
Anderson, M., Schroer, B., & Moeller, D. (2012). Analyzing the diverging diamond interchange using discrete event simulation. Modelling and Simulation in Engineering , 2012 , 47.
Blincoe, L. J., Miller, T. R., Zaloshnja, E., & Lawrence, B. A. (2015, May). The economic and societal impact of motor vehicle crashes, 2010. (Revised) (Report No. DOT HS 812 013). Washington, DC: National Highway Traffic Safety Administration.
Edara, P., Sun, C., Claros, B. R., & Brown, H. (2015). Safety Evaluation of Diverging Diamond Interchanges in Missouri (No. cmr 15-006). Report cmr.
Florida Department of Transportation. (2016). I-75 (SR 93) at University Parkway Diverging Diamond Interchange (DDI). Retrieved from: https://www.scgov.net/PublicWorks/Documents/Diverging%20Diamond%20Interchange %20Fact%20Sheet.pdf
Le Coz, E. (2016). I-75 diverging diamond construction on schedule. Herald Tribune . Retrieved from: http://www.heraldtribune.com/article/20160102/ARTICLE/160109963?tc=ar
Morris, D. (2016). New "Diverging Diamond" Intersection Design Cuts Crashes by Sixty Percent. Fortune. Retrieved from: http://fortune.com/2016/06/05/diverging-diamond- intersection/
