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36 CHAPTER 10 CASE STUDY 2: CLOSE FREEWAY LANE--URBAN Case Study 2 removes a single through lane in each direc- 10.2 CASE STUDY RESULTS tion of a freeway in an urban area. The freeway is uncon- gested under the base 2020 condition, but deleting the lane The NCHRP 25-21 methodology was used to compute the USER'S GUIDE makes the freeway congested. impacts of the traffic-flow improvement on the 2020 base The specific location for this case study is a 6.6-mile-long case trip tables by time period (AM peak, PM peak, and off section of the State Route 520 freeway (the Evergreen Point peak) and by mode (SOV, HOV, and transit). The revised trip Bridge) between the I-5 and I-405 interchanges in Seattle, tables were then reassigned to the improved network to deter- Washington (see Figure 7). mine the impact on VMT, VHT, and emissions. The results are summarized in Tables 24 through 26. This case study illustrates how removing or closing a free- 10.1 APPLICATION way lane causes an initially uncongested freeway to become congested during the peak periods. This action reduces peak- Before the improvement, this section had three lanes in each period travel on the facility significantly, but has a very small direction. Note that this section also has a barrier-separated effect on regional travel (VMT). HOV lane in each direction. Because the links were not very The mean speed on the facility is reduced significantly, and congested with three lanes (peak-period volume/capacity the mean travel time is increased significantly (on the order ratio was less than 1.00), a lane was removed in each direc- of 30 to 50 percent). Reverse commute directions are less tion so as to provide a case study where the impacts of an affected. Peak-period volumes are reduced by about 15 per- improvement were to make conditions more congested. Thus, cent, while off-peak travel is relatively unaffected. Total daily after the "improvement," the section has two lanes in each VMT is changed by less than 0.01 percent. Total emissions of direction with a barrier-separated HOV lane. No change was THC, CO, and NOX are reduced by 0.2 to 0.4 percent. made in the 50- to 60-mph free-flow speed and the 1,800- to The net effect of closing the freeway lane is to reduce daily 1,850-vehicles/hour/lane capacity for this freeway. vehicle emissions by 0.2 to 0.4 percent.

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37 USER'S GUIDE Project Figure 7. Case Study 2: Delete lane from SR 520 Evergreen Point Bridge. TABLE 24 Case Study 2: 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 0.45 48.5 8.55 0.78 47.9 8.62 After 0.61 44.7 9.28 0.94 43.6 11.19 Difference 0.16 -3.7 0.73 0.17 -4.3 2.57 % Difference 36.05% -7.72% 8.54% 21.48% -8.98% 29.81% PM Peak Before 0.82 48.5 8.55 0.66 47.9 8.62 After 0.92 45.1 13.22 0.93 47.3 8.72 Difference 0.10 -3.4 4.67 0.27 -0.6 0.10 % Difference 12.22% -6.93% 54.62% 41.69% -1.25% 1.16% Off Peak Before 0.32 48.5 8.55 0.32 47.9 8.62 After 0.47 48.5 8.55 0.48 47.9 8.62 Difference 0.16 0.0 0.00 0.16 0.0 0.00 % Difference 49.73% 0.00% 0.00% 49.71% 0.00% 0.00% TABLE 25 Case Study 2: Volume changes on the facility Period Direction Before After Difference %Difference AM Peak EB 7,445 6,755 -691 -9.28% WB 12,808 10,372 -2,435 -19.02% TOT 20,253 17,127 -3,126 -15.43% PM Peak EB 13,495 10,097 -3,398 -25.18% WB 10,835 10,236 -600 -5.53% TOT 24,330 20,333 -3,998 -16.43% Off Peak EB 31,369 31,314 -56 -0.18% WB 31,526 31,465 -62 -0.20% TOT 62,896 62,778 -117 -0.19% Total EB 52,310 48,165 -4,144 -7.92% WB 55,170 52,073 -3,097 -5.61% TOT 107,479 100,238 -7,241 -6.74%

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38 TABLE 26 Case Study 2: 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 12,156,500 381,945 31.8 PM Peak 15,259,800 519,266 29.4 Off Peak 37,207,400 1,179,100 31.6 Total 64,623,700 2,080,311 31.1 44,914,702 712,081,618 46,184,899 Difference 300 1,349 0.0 -85,484 -1,983,263 -171,980 % Difference 0.00% 0.06% -0.06% -0.19% -0.28% -0.37% USER'S GUIDE