ITE Journal - March 2021 - 40

Courtesy MTJ Roundabout Engineering.

example showing application of landscaping the splitter island as
well as the central island to address the driver expectancy of this
high speed context divided highway application.
Accommodating Large Vehicles. The ability to design a
roundabout for typical design vehicles (WB-62 or WB-67) as well
as oversized over weight (OSOW) trucks or farming equipment is
essential to the success of a project. Not only are there tools available
to assist with simulating the larger vehicles, there are also flexibilities
in design features such as truck apron width and shape, outside
curbing design and location, as well as modifications to the splitter
island noses and curbing. This is often where experience in applying
engineering principles for both roadway and roundabout specific
applications come into play to achieve desired accommodations
without reducing overall safety. There are physical limitations of
large vehicles to make particular turns maneuvers-even with
skilled and professional drivers-in addition to the roundabout
design features that are needed for speed control and consistency.
How those elements come together is part of the problem solving
and creativity of roundabout design. The project examples shown in
Figure 3 show an elliptical center islands and raised features modified
to accommodate the large, yet likely infrequent, trucks traversing the
intersection. Lastly, it is important to engage the trucking and freight
community in conversations early on regarding the use (i.e., what are
the predominant movements through the intersection?).
Divided Highways. Rural divided highways are found across the
tranpsortation landscape. Like rural two-lane roadways, there are
decisions and conflicts at these higher volume rural intersections.
High speeds are expected, and gaps in high-speed traffic can be
a challenge to find during portions of the day. A roundabout is a
viable design alternative to other intersection options. Even with
unbalanced flows between the major route and minor route, a
roundabout can provide safety benefits to both mainline and side
street traffic as they navigate turning movements. The safety project

Figure 3. OSOW Wind Tower AutoTurn Turning Template
and Envelopes.

Jaye Street/Montgomery Avenue, Porterville, CA, USA.
40

Ma rch 2021

ite j o u rn al

Courtesy MTJ Roundabout Engineering.

Courtesy GHD.

shown in Figure 4 evaluated a roundabout, grade separation, and
a signal to replace a two-way stop control intersection with a very
poor safety record. During the evaluation stage of the project,
the roundabout was shown to substantially outperform the other
two alternatives with respect to benefits and cost, and it fit the
community's goals of providing a gateway. It was constructed in
2006 and has had an exemplary safety record, which is attributed to
its high level of design features that addressed the driver expectancy
requirements of this high-speed roadway.
Lighting. Intersection lighting is very common at roundabouts
and is a requirement for many states, several of which have
roundabout lighting guidance. Intersection lighting is one feature
that contributes to the visibility of the intersection as drivers
approach the rural intersection. The number and location of
light poles-and therefore, luminance-typically varies based
on roadway traffic volumes, adjacent land use, pedestrian and
bicyclist use, length of splitter islands, and other intersection
signage. According to a 2016 publication, highway lighting can

Figure 4. Divided highway in Dodgeville, WI US Hwy 18 at
Bennett Rd Intersection.



ITE Journal - March 2021

Table of Contents for the Digital Edition of ITE Journal - March 2021

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