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39 CHAPTER 11 CASE STUDY 3A: REMOVE FREEWAY HOV LANE Case Study 3a removes the freeway HOV lanes (one HOV 11.2 CASE STUDY RESULTS lane in each direction) from a freeway in an urban area. The freeway is uncongested before and after the removal of The NCHRP 25-21 methodology was used to compute the USER'S GUIDE the lanes. impacts of the traffic-flow improvement on the 2020 base The specific location for this case study is a 2.1-mile- case trip tables by time period (AM peak, PM peak, and off long section of the I-405 freeway between the S.E. 181st peak) and by mode (SOV, HOV, and transit). The revised trip and SR 169 interchanges in Renton, Washington (see Fig- tables were then reassigned to the improved network to deter- ure 8). mine the impact on VMT, VHT, and emissions. The results are summarized in Tables 27 through 29. This case study illustrates the impacts of closing the HOV lanes on an existing, uncongested freeway. The action has no 11.1 APPLICATION significant effect on speeds and travel times for the mixed- flow lanes, but because it closes an HOV facility, there is a The I-405 freeway mainline has significant effect on facility volumes. Peak-period volumes on the freeway increase by 12 to 20 percent. Daily volumes Four lanes in each direction with a 45-mph free-flow are increased by slightly less than 10 percent. speed and a 1,800-vph/lane capacity and Total regional VMT is increased by 0.02 percent, but An HOV lane in each direction with a 60-mph free-flow mobile source emissions are decreased by 0.02 to 0.04 percent. The slight speed increase appears to have overcome the slight speed and a 1,500-vph/lane capacity. VMT increase. This may be the result of a model coding prac- tice that gives the HOV lane lower free-flow speeds and capac- In this project, the HOV lanes in both directions are ities than mixed-flow lanes on a freeway. Fewer HOVs in the removed. Thus, the section now has four lanes in each direc- HOV lanes may have slightly boosted the regional mean speed tion and no HOV lane. of all traffic.

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40 USER'S GUIDE Project Figure 8. Case Study 3a: I-405 Renton. TABLE 27 Case Study 3a: 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 0.46 43.0 4.18 0.64 43.2 4.14 After 0.58 43.0 4.18 0.74 43.2 4.14 Difference 0.12 0.0 0.00 0.10 0.0 0.00 % Difference 25.58% 0.00% 0.00% 16.43% 0.00% 0.00% PM Peak Before 0.81 43.0 4.18 0.75 43.2 4.14 After 0.89 43.0 4.18 0.86 43.2 4.14 Difference 0.08 0.0 0.00 0.10 0.0 0.00 % Difference 10.11% 0.00% 0.00% 13.76% 0.00% 0.00% Off Peak Before 0.32 43.0 4.18 0.31 43.2 4.14 After 0.34 43.0 4.18 0.32 43.2 4.14 Difference 0.02 0.0 0.00 0.02 0.0 0.00 % Difference 5.72% 0.00% 0.00% 5.98% 0.00% 0.00% TABLE 28 Case Study 3a: Volume changes on the facility Period Direction Before After Difference %Difference AM Peak EB 9,991 12,547 2,556 25.58% WB 13,718 15,972 2,254 16.43% TOT 23,709 28,519 4,810 20.29% PM Peak EB 17,410 19,171 1,761 10.11% WB 16,305 18,547 2,243 13.76% TOT 33,714 37,718 4,004 11.87% Off Peak EB 41,681 44,063 2,383 5.72% WB 39,612 41,980 2,369 5.98% TOT 81,292 86,043 4,751 5.84% Total EB 69,081 75,780 6,699 9.70% WB 69,635 76,500 6,865 9.86% TOT 138,716 152,280 13,564 9.78%

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41 TABLE 29 Case Study 3a: 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 12,157,300 381,813 31.8 PM Peak 15,264,100 517,755 29.5 Off Peak 37,212,500 1,179,300 31.6 Total 64,633,900 2,078,868 31.1 44,988,995 713,780,208 46,344,037 Difference 10,500 -94 0.0 -11,191 -284,673 -12,842 % Difference 0.02% 0.00% 0.02% -0.02% -0.04% -0.03% USER'S GUIDE