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. Data Collection 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 Study Sites 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 w w w .i t e.or g Apri l 2018 47