Submitted by Ken Watts.
Three traffic studies/reports have been completed for US 20 roughly between Ashton and SH 87. The first was completed in 2006, the second in 2019, and the last in February of 2022. Each study used a different method to determine the traffic volume to be used to determine the level of service for the road. The best way to understand the different methods is to read quotes from the studies. The first quote is from the 2006 study written by HDR Transportation Engineering: “Perhaps the most challenging issue confronted during the US 20 corridor planning process is the widely fluctuating traffic volumes. This fluctuation results from a higher than average seasonal variation in use, which reflects the primary summer recreation-related uses on and through the corridor. Traffic volumes reach an annual high in July and a low in January. Permanent traffic counters recorded traffic volumes in July as approximately 98 percent higher than the annual average daily traffic, and in January, traffic volumes drop 52 percent below the annual ADT. This puts summer volume highs at approximately five times greater than winter volume lows.….. A significant factor in determining appropriate improvements is the assessment of Design Hour Volume (DHV). Design Hour Volumes are commonly calculated using the 30th highest hour for the roadway, typically around 85 percent of the peak hour of traffic for the road on an annual basis. However, on US 20, the 30th highest hour is well over 90 percent of the peak hour for the road due to the makeup of the traffic using the highway (i.e. seasonal and weekend traffic). This creates concerns that improvements planned to accommodate DHV’s using this method will likely exceed the routine capacity needs for the corridor and would not support ITD’s goal of context sensitive design…. To address concerns that recommendations should be appropriate for the majority of the corridor’s traffic volumes and context sensitive, an alternative methodology was used. The Alternative Capacity Analysis method for calculating DHV is described in the AASHTO Greenbook and multiplies the average of the top three hours on the corridor by 50 percent. This analysis may or may not yield a lower traffic volume, but it should provide a LOS result that is more reflective of the actual traffic situation. This methodology is called out specifically for use in the situation where a highly seasonal use roadway is being analyzed. For the US 20 corridor, it was determined that this method would be used…...” The second quote is from the 2019 traffic study done by JUB Engineers, Inc.: “The 2016 plan states that it captures the summer recreation period by using the 30th highest hour methodology in determining the design hour volume. The 30th highest hour volume calculated in the 2016 plan was higher than the design hourly volume used in the 2006 study, which can be attributed to the methodology applied in each study, as well as a 30% increase in traffic volumes on the study section of US 20 since the 2006 study was completed.” The third quote is from the 2022 traffic study completed by Horrocks Engineers: “Traffic data used to calculate the Level of Service was collected in 2018 and a 3.4% linear growth rate was applied to each location to project to the year of 2021 and to the horizon year of 2050. Because this roadway has high seasonal fluctuations in traffic volume, the peak hour volumes were selected based on the average four highest months (June-September).” Do you see how the goalposts moved? The first study said it was inappropriate to use the 30th highest hour methodology. The second study used this methodology. The third escalated the design traffic volume by using the peak hour volumes for June to September. Why should you care? The third and last approach will result in gross over design of US 20 and will be used to justified a 4 lane, high speed highway through Island Park. It will result in significant environmental damage.
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