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45 CHAPTER 13 CASE STUDY 4: NARROW STREET Case Study 4 removes a single through lane from each case trip tables by time period (AM peak, PM peak, and off direction of an uncongested suburban highway. The specific peak) and by mode (SOV, HOV, and transit). The revised trip location for this case study is a 10.1-mile-long section of State tables were then reassigned to the improved network to deter- USER'S GUIDE Route 169 between I-405 and SR 18 near Renton, Washington mine the impact on VMT, VHT, and emissions. The results (see Figure 10). are summarized in Tables 33 through 35. This case study illustrates the impacts of removing a mixed-flow lane in each direction from a rural highway that 13.1 APPLICATION is near capacity. The effect is to cause modest congestion in the peak direction of travel during each peak period. Peak- The project removes one mixed-flow lane in each direction period travel times increase 6 to 10 percent in the peak direc- to SR169, the Renton-Maple Valley Highway. Before the tions only. Total daily traffic volumes drop about 7 percent. case study changes, SR 169 has a single-lane HOV and two The net effect of the lane removal on regional VMT and lanes in each direction. Thus, the project results in the sec- emissions is less than 0.01 percent. tion having one mixed-flow lane and a single HOV lane in each direction. 13.2 CASE STUDY RESULTS The NCHRP 25-21 methodology was used to compute the impacts of the traffic-flow improvement on the 2020 base

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46 Project USER'S GUIDE Figure 10. Case Study 4: Remove through lane from SR 169. TABLE 33 Case Study 4: 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 0.07 35.8 17.19 0.30 35.7 17.22 After 0.13 35.8 17.19 0.47 32.8 18.25 Difference 0.07 0.0 0.00 0.18 -2.9 1.03 % Difference 100.22% 0.00% 0.00% 59.59% -8.22% 5.98% PM Peak Before 0.29 35.8 17.19 0.13 35.7 17.22 After 0.46 31.7 18.82 0.25 35.7 17.22 Difference 0.18 -4.1 1.63 0.12 0.0 0.00 % Difference 60.70% -11.55% 9.48% 98.87% 0.00% 0.00% Off Peak Before 0.08 35.8 17.19 0.07 35.7 17.22 After 0.16 35.8 17.19 0.14 35.7 17.22 Difference 0.08 0.0 0.00 0.07 0.0 0.00 % Difference 98.03% 0.00% 0.00% 98.00% 0.00% 0.00% TABLE 34 Case Study 4: Volume changes on the facility Period Direction Before After Difference %Difference AM Peak EB 568 568 0 -0.06% WB 2,517 2,002 -515 -20.47% TOT 3,085 2,569 -516 -16.71% PM Peak EB 2,464 1,976 -488 -19.81% WB 1,066 1,058 -8 -0.73% TOT 3,530 3,034 -496 -14.05% Off Peak EB 4,217 4,175 -42 -0.99% WB 3,728 3,690 -37 -1.00% TOT 7,944 7,865 -79 -0.99% Total EB 7,249 6,719 -530 -7.31% WB 7,311 6,750 -560 -7.66% TOT 14,559 13,469 -1,090 -7.49%

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47 TABLE 35 Case Study 4: 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 12,154,000 381,502 31.9 PM Peak 15,260,900 518,126 29.5 Off Peak 37,207,400 1,179,100 31.6 Total 64,622,300 2,078,728 31.1 44,998,481 714,063,588 46,356,164 Difference -1,100 -234 0.0 -1,705 -1,293 -715 % Difference 0.00% -0.01% 0.01% 0.00% 0.00% 0.00% USER'S GUIDE