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33 CHAPTER 9 CASE STUDY 1: ADD FREEWAY LANE--RURAL Case Study 1 adds a single through lane to each direction flow speed and the 1,800-vehicles/hour/lane capacity for this of a freeway in a rural mountainous area. The freeway is freeway. uncongested under the base 2020 condition; thus, adding the USER'S GUIDE lane has no effect on the operating speeds of vehicles on the 9.2 CASE STUDY RESULTS freeway. The specific location for this case study is a 7.6-mile-long The NCHRP 25-21 methodology was used to compute the section of the Interstate 90 freeway between the S.E. 68th impacts of the traffic-flow improvement on the 2020 base Street Interchange and the SR 202 Interchange near North case trip tables by time period (AM peak, PM peak, and off Bend, Washington (see Figure 6). peak) and by mode (SOV, HOV, and transit). The revised trip tables were then reassigned to the improved network to deter- mine the impact on VMT, VHT, and emissions. The results are summarized in Tables 21 through 23. 9.1 APPLICATION This case study is an example of an unnecessary capacity improvement being placed at a location where there is already The 2020 base case has four lanes in the uphill direction and plenty of excess capacity. The extra capacity on the freeway three in the reverse direction. The project adds one through has no effect on the speed of traffic on the freeway, which is lane in each direction over the entire length of the project. all traveling at the free-flow speed during both the peak and Thus, after the improvement, there are five lanes in the uphill off-peak periods. The result is that the capacity improvement direction, including truck-climbing lanes, and four lanes in the has no effect on travel times, trip making, VMT, or emissions, reverse direction. There was no change in the 70-mph free- as expected.

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34 USER'S GUIDE Project Figure 6. Case Study 1: I-90 North Bend. TABLE 21 Case Study 1: Travel time changes on the facility Period Scenario EB WB V/C Speed (mph) Time (min) V/C Speed (mph) Time (min) AM Peak Before 0.10 69.3 6.54 0.18 69.7 6.51 After 0.07 69.3 6.54 0.14 69.7 6.51 Difference -0.02 0.0 0.00 -0.04 0.0 0.00 % Difference -24.17% 0.00% 0.00% -21.94% 0.00% 0.00% PM Peak Before 0.21 69.3 6.54 0.11 69.7 6.51 After 0.16 69.3 6.54 0.09 69.7 6.51 Difference -0.05 0.0 0.00 -0.02 0.0 0.00 % Difference -23.77% 0.00% 0.00% -21.44% 0.00% 0.00% Off Peak Before 0.08 69.3 6.54 0.06 69.7 6.51 After 0.12 69.3 6.54 0.10 69.7 6.51 Difference 0.04 0.0 0.00 0.04 0.0 0.00 % Difference 51.33% 0.00% 0.00% 56.23% 0.00% 0.00% TABLE 22 Case Study 1: Volume changes on the facility Period Direction Before After Difference % Difference AM Peak EB 1,643 1,643 0 0.00% WB 3,545 3,545 0 0.00% TOT 5,188 5,188 0 0.00% PM Peak EB 3,623 3,623 0 0.00% WB 2,299 2,299 0 0.00% TOT 5,922 5,922 0 0.00% Off Peak EB 15,830 15,830 0 0.00% WB 14,904 14,904 0 0.00% TOT 30,735 30,735 0 0.00% Total EB 21,096 21,096 0 0.00% WB 20,749 20,749 0 0.00% TOT 41,844 41,844 0 0.00%

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35 TABLE 23 Case Study 1: Regional results Scenario Period VMT VHT Speed THC CO NOX (mi) (hrs) (mph) (gm) (gm) (gm) Before AM Peak 12,152,900 381,540 31.9 PM Peak 15,261,700 518,222 29.5 Off Peak 37,208,800 1,179,200 31.6 Total 64,623,400 2,078,962 31.1 45,000,186 714,064,881 46,356,879 After AM Peak 12,152,900 381,540 31.9 PM Peak 15,261,700 518,222 29.5 Off Peak 37,208,800 1,179,200 31.6 Total 64,623,400 2,078,962 31.1 45,000,186 714,064,881 46,356,879 Difference 0 0 0.0 0 0 0 % Difference 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% USER'S GUIDE