The document discusses diverging diamond interchanges (DDIs), a new intersection design that improves traffic flow and safety. It provides background on traditional interchanges and their issues with left turns and congestion. The DDI design is then explained, noting its crisscross lane pattern eliminates dangerous left turns by having them function as right turns. Studies showed DDIs reduced conflict points and errors while increasing speeds safely. The first DDI constructed in Missouri significantly reduced congestion and crashes compared to the previous interchange. Future development of additional DDIs is discussed to further address traffic problems.

1. Transportation
Term Paper
Diverging Diamond Interchanges
Table of Contents
Abstract
Page 3
Introduction
Page 3
Current Interchanges
Page 3
Diverging Diamond Interchange
Page 4
Traffic Studies
Page 5
Future Development
Page 6
Conclusion
Page 6
References
Page 7

2. Abstract
Introduction
Traffic, we all have experienced the headaches it brings. At an
intersection is where the potential conflict is most likely to
occur, especially between two major traffic arteries. The goal of
traffic engineering is to provide the most efficient means of
alleviating the traffic conflicts. However, in areas with
increasing traffic demands that the traditional methods have
been insufficient in dealing with the higher traffic. Therefore a
new intersection design was developed known as the diverging
diamond interchange. The diverging diamond interchange
utilizes channelization and a crisscross lane pattern to reduce
traffic conflict points. Studies have shown that commuters using
a diverging diamond interchange feel safer than they do using
traditional interchanges. Along with being safer, the diverging
diamond interchange is more cost effective than alternative
interchanges by utilizing existing infrastructure for its design.
Current Interchanges

3. Interchanges are a specific classification of intersections which
are constructed to provide un-interrupted flow for crossing
traffic by changing the elevation between the roadways. Due to
this, ramps are required to connect the crossing traffic and
allow turning from one to the other. In the usual interchange
traffic wanting to turn left has to cross oncoming traffic to enter
or exit a ramp perpendicular to vehicle’s current direction.
Therefore a left turning vehicle is at a greater risk getting
involved in a serious collision when crossing oncoming traffic
that may result in fatalities then the through or right turning
traffic. Majority of the fatal crashes at an interchange occur
from the unprotected left turn.
There are measures of left turn protection with minimal
altercations to the design of the intersection. Designing an
intersection with left turn protection adds additional cycles to
the traffic signal providing more green time for left turning
traffic and prevents oncoming traffic from moving. Also, when
necessary, extra left turn lanes may be required storage
isolating the through traffic. However, a longer cycle length due
to left turn protection causes its own problems, in high traffic
interchanges. This is because there is longer red time for traffic
in other directions when the left turn cycles are added to at an
intersection.
Furthermore, when there is too great of a demand for any
particular interchange another issue arises, traffic can become
backed up causing a delay even after adjusting the signal
timing. Traffic backed up at one intersection far enough will
affect the traffic flow at other intersections along the same
traffic artery even when there are multiple lanes. To
accommodate an increase in traffic volumes addition
infrastructure is added such as super elevated ramps and bridges
which can become costly depending on the layout and footprint
of the new infrastructure. Is there a better way? To increase
efficiency, the diverging diamond interchange may be the
solution in areas where the current interchange design is failing
to keep up with the higher traffic volumes.

4. Diverging Diamond Interchange
The Diverging Diamond Interchange or DDI features a
crisscross flow direction with shallower angles at the
intersections this configuration can be seen in the figure 1.
Another feature in the design is the unique left turn, since the
directions of travel switched the vehicles in the farthest left
lane can perform their left turn onto the ramp in a similar manor
as a right turn would be made at standard interchange.
Therefore, no left turning ever crosses oncoming traffic while
making the turn which is much safer and more efficient.
Figure 1
(Source from: Diverging Diamond Interchange Informational
Guide by Schroeder, 2014)
The DDI design is relatively new to the United States the prior
to 2000 this interchange design was unheard of until Gilbert
Chlewicki, currently the ATS/American’s division director
published his paper on this design titled “New Interchange and
Intersection Designs: The Synchronized Split-Phasing
Intersection and the Diverging Diamond Interchange” in July of
2003. The diverging diamond Interchange design caught Joe
Bared, PhD, PE from the Federal Highway Administration
(FHWA), attention. Bared, performed an evaluation of the
design and released his results in 2005 with promising remarks
for the design (Chlewicki, 2014). The design was untested in
reality until 2009 where in Springfield, Missouri the first
diverging diamond interchange was constructed. The 3 million
dollar project between I-44 and the Missouri SR 13 cost
significantly less than the traditional interchange of 10 million
dollars. This was achieved because there was no substantial
construction needed and the existing bridge over I-44 was
adequate enough for the DDI. After opening, the response from
the public was better than anticipated many and the theory
behind the diverging diamond interchange of being efficient and
safer was proven to be true (Chlewicki, 2014).
Traffic Studies

5. Safety is always a major concern for a new design, the
DDI was no exception. A DDI in theory is safer than the
standard diamond interchange because there is a reduction of
points of conflict shown in Table 1. Majority of fatal crashes at
traditional diamond interchanges occur when crossing traffic
depending on the layout of the interchange there are 10 crossing
points of conflict in the conventional diamond interchange.
These conflict points generate the T-bone and head on collisions
which often in fatal crashes. The DDI has only 2 points for
crossing conflicts also the crossing itself has been modified to
provide angles that reduce the severity of a crossing collision
and discourages driving into oncoming traffic as well since the
flow directions swap (Federal, 2016).
Table 1
○ Diverging
● Merging
● Crossing
The diverging diamond interchange points of conflict can be
found that there are 14 in total.
Diverging traffic conflicts usually are minor crashes
Merging traffic conflicts usually are minor crashes
Crossing traffic conflicts usually are major crashes
The conventional diamond interchange points of conflict can be
found that there are 26 in total
Diverging traffic conflicts usually are minor crashes
Merging traffic conflicts usually are minor crashes
Crossing traffic conflicts usually are major crashes
(Sourced from Crossover-Based Intersections by the Federal
Highway Administration, 2016)
Before the first DDI was constructed in Missouri, the Missouri
Department of Transportation (MoDOT) and the FHWA
developed a traffic simulator to fully test the effectiveness and
efficiency of the diverging diamond interchange design as well
as optimize the location for signals and signs. During their

6. study, the FHWA selected 74 participants to add a human factor
to the DDI simulation the results were as follows in Table 2.
Table 2
Interchange Type
Green Traffic Signal Style
Directional Pavement Marking and Signs
Wrong Way signs at Crossovers and Arterial
Navigation Errors (legal But Incorrect Turns)
Red light signal Violations (Illegal)
Mean Speed at Crossovers (mph)
DDI
Arrow
Yes
Yes
17/827
2/255
23.2
DDI-M
Ball
No
No
19/809
5/277
24.6
Diamond
Ball
N/A
N/A
21/814
7/354
34.4
(Sourced from Drivers' Evaluation of the Diverging Diamond
Interchange by Bared, 2007)
The results of the study shows that the DDI is viable alternative
interchange design combining operational benefits with
increased safety.

7. In Springfield, Missouri between I-44 and the Missouri SR
13 where the first diverging diamond interchange was
constructed. Saw significant reductions in traffic congesting and
in traffic collisions over the previous interchange after
completion of the DDI. Post construction a public survey
conducted by MoDOT found that 95 percent of drivers agreed
the roadway was less congested. Another study shows that the
total crashes declined 46 percent when comparing the average
across the 5-year baseline to the one-year post-construction
period of 24 percent reduction in total crashes (Shaw & Doctor,
2015). The DDI possible could become the preferred
interchange design.
Future Development
The second diverging diamond interchange in Ohio began
construction on September 28, 2016 at I-475 and Ohio SR 25 in
Perrysburg. At the current interchange there has been major
congestion the Toledo Metropolitan Area Council of
Governments and the Ohio Department of Transportation
anticipate that the DDI should help ease traffic movement
through the congested SR 25 and I-475 interchange. The project
costs 8.75 million dollars and should take a year to complete.
The DDI will utilize the existing bridge over I-475 therefore
reducing costs however the existing on and off ramps will be
replaced to accommodate the DDI’s distinctive arcing approach
and storage lanes. DGL Consulting Engineers designed the DDI
and the project was awarded to E.S. Wagner as the general
contractor (Maiolo, 2016).
Conclusion

8. References
Bared, J. G. (2007, September 25). Drivers' Evaluation of the
Diverging Diamond Interchange (United States, Federal
Highway Administration, Office of Safety Research
Development and Technology). Retrieved November 2, 2016,
from
https://www.fhwa.dot.gov/publications/research/safety/07048/
Chlewicki, G. (2014). The Diverging Diamond Interchange
Website. Retrieved October 31, 2016, from
http://divergingdiamond.com/index.html
Federal Highway Administration. (2016, May 26). Crossover-
Based Intersections. Retrieved November 05, 2016, from
http://safety.fhwa.dot.gov/intersection/innovative/crossover/
Garber, N. J., & Hoel, L. A. (2015). Traffic and Highway
Engineering (5th ed.). Stamford, CT: Cengage Learning.
Maiolo, J. (2016, October 5). ODOT Begins Work on Divergent
Diamond Interchange. Perrysburg Messenger Journal, p. 1.
Schroeder, B. J., Cunningham, C., Ray, B., Daleiden, A., Jenior,
P., Knudsen, J., & Kittelson & Associates, Inc.
(2014). Diverging Diamond Interchange Informational Guide
[PDF].
Shaw, J., & Doctor, M. (2015, December 1). Interstate 44 and
Missouri Route 13, Springfield, MO; Diverging Diamond
Interchange. Retrieved November 05, 2016, from
http://safety.fhwa.dot.gov/intersection/innovative/crossover/cas
e_studies/mo/