Submitted by Ken Watts
Last week Ken’s Korner introduced you to a “Preliminary Traffic Operations Report” for US 20 between Ashton and SH 87, produced by Horrocks Engineers, for the Idaho Department of Transportation. This traffic report was based on incomplete data from 2018 and “fudge factors” were applied to project the data to 2021 and 2050. 32 years into the future. Horrocks did traffic projections for the highest traffic summer months and the highest traffic hour. Read last week’s Ken’s Korner for details on the suspect assumptions. This week we will examine how Horrorks Engineers calculated the level of service (LOS) for 24 US 20 road segments between Ashton and SH 87. There are 6 levels of service, A thru F. A is the best service and F is the worst. For US 20, ITD wants a level of service of B for rolling rural areas and C for mountainous areas. To get the 2021 traffic density, they increased the 2018 traffic data by 3.4% linearly based on one traffic camera located near Sheep Falls. So, in 10 years, the traffic would increase by 34% and in 32 years it would increase by 108.8% using this approach. Horrocks Engineers used the McTrans Highway Capacity Software HCS7 to calculate the LOS for the 24 road segments for the years 2021 and 2050. The calculation is based on physical highway features, like lane width, and the “peak” traffic volume among other things. Horrocks Engineers concluded that in 2021 only 7 of the 24 northbound segments meet the minimum LOS and 10 of the 24 southbound segments meet the minimum LOS. In 2050 only one northbound segment and no southbound segments would meet the minimum LOS. Remember that in 2050, ITD predicted that traffic will be 108.8% higher than 2018. Now let’s look at whether the computer program provides good predictions of the level of service for the 24 road segments. The best way to do this is to look at Figures 7 and 8 in the report and look at the calculated speed in 2021. The computer program says the average travel speed in Last Chance is 29.1 mph northbound during the peak hours, 32.9 at Ponds Lodge, 30.4 at Elk Creek, 29.8 at Mack’s Inn, 30.2 at Sawtelle, and 31.2 at Valley View. Think back to 2021. Did you ever drive thru these areas at these low speeds in 2021? If you did, you would likely have a tourist or a semi driving up your tailpipe! The point is that the computer program is generating ridiculously low travel speeds. This results in poor predictions of the level of service for these and other segments of the road. Further, it leads to justifying a four lane, high speed highway thru Island Park and possibly bypassing local businesses. One can only conclude that this traffic report is flawed. ITD should conduct a new traffic study, with real data, not calculated data, before committing 10’s of millions of dollars to this project. Let’s get it right. No phony calculations and assumptions. This results in a poor level of service for road segments between Ashton and SH 87. The rest of the year, the level of service is just fine, with great levels of service.
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This blog will help you make sense out of all the information on the website, how it affects IP, our history, and how efforts continue to put IP into various forms of conservation status. Archives
May 2023
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