ITE Journal April 2018 - 47
study location in Dallas, TX, USA.8 The location was identified
to be the originating point of several WWD incidents due
to a side street closely placed to an exit ramp which resulted
in left-turn drivers wrongly entering the exit ramp instead
of the side street from the crossroad. To mitigate wrong-way
movements, the NTTA closed the median opening to prohibit
left turns into the side street. Afterwards, no WWD incidents
were recorded at this location.
According to Morena and Ault, longitudinal channelization
devices can also be used as low-cost geometric countermeasures
by transportation agencies to deter WWD crashes.9 The Michigan
Department of Transportation (MDOT) applied this countermeasure to one high WWD crash location in 2010. Since 2012, no
WWD crashes were reported at this location after the treatment.
No specific guideline exists for stop line positioning for left
turns onto entrance ramps at parclo interchange terminals in
the Manual on Uniform Traffic Control Devices (MUTCD) or
American Association of State Highway and Transportation
Officials (AASHTO) Green Book.3,10 In 2013, the Washington
State Department of Transportation proposed that the distance
between the stop line for left turns from a crossroad and the
middle of the median separating on and off ramps be no more
than 60 percent of the entire intersection width (Figure 2).11 The
green line illustrates the right-way movements, while the red line
represents the wrong-way movements.
entire intersection, which makes the entrance ramp difficult to be
seen by left-turn drivers and creates a large turning radius.
Figure 3. Example of unbalanced intersections.2
A recent study by Wang et al. with 10-year (2004-2013)
Illinois WWD crash data concluded there is no guideline in the
current MUTCD indicating the appropriate design of stop line
positioning.12 Notwithstanding, the stop line positionings among
50-60 percent is used most often at parclo interchange terminals.
Additionally, the possibility of WWD crashes increases significantly when the stop line on crossroads is positioned more than
60 percent into the intersection at signalized terminals for parclo
interchanges based on WWD crash analysis.
Past research proved the effectiveness of the application of
some geometric elements in mitigating wrong-way movements
at parclo interchange terminals, including using raised median
and channelizing islands, increasing the median width between
exit ramps and entrance ramps, and reducing the turning
radius, but their detailed impacts on WWD movements have not
been evaluated. Accordingly, statistical analyses were performed
to examine how different geometric elements may factor in
WWD, and then outline how the research may fill the gaps in
research and address the impact of specific geometric elements
to improve safety.
Variable identification and Varification
Figure 2. Current best practice of stop line positioning.
However, there is lack of scientific research to support the
proposals outlined by WSDOT. Figure 3 shows an example of
unbalanced intersections where WWD crashes and incidents were
recorded.2 The distance between the stop line for north bound left
turns and the median centerline is more than 60 percent of the
Forty-four signalized ramp parclo interchange terminals in Illinois
were identified as study locations based on high-resolution aerial
photography, street views, and the geographic information system
(GIS) capabilities of Google Earth Professional software. The
coordinates of each study location were recorded. All left-turning
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Apri l 2018