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CHAPTER 16
CASE STUDY 7: SIGNAL COORDINATION
Case Study 7 tests the impacts of a 0.5-mile-long arterial case trip tables by time period (AM peak, PM peak, and off
signal coordination project that increases mean speeds by 10 peak) and by mode (SOV, HOV, and transit). The revised trip
percent. The specific location for this case study is Montblake tables were then reassigned to the improved network to deter-
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Boulevard, at the University of Washington in Seattle (see Fig- mine the impact on VMT, VHT, and emissions. The results
ure 13). The project consists of six signals over 0.54 miles. are summarized in Tables 44 through 46.
This case study illustrates the impacts of the optimization
16.1 APPLICATION of signal coordination for a 0.5-mile section of urban arter-
ial. The improvements provide a 9-percent reduction in
The signal coordination project is coded as a 10-percent travel times for the peak direction of the peak periods and a
improvement in the free-flow speed. No capacity changes similar reduction for both directions during the off-peak
were made. period. Daily traffic on the facility is predicted to increase
by 27 percent.
The net effect on regional travel is to reduce regional VMT
16.2 CASE STUDY RESULTS
by 0.01 percent and to reduce regional emissions by 0.02 to
The NCHRP 25-21 methodology was used to compute the 0.04 percent.
impacts of the traffic-flow improvement on the 2020 base
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Project
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Figure 13. Case Study 7: Montblake Boulevard, Seattle.
TABLE 44 Case Study 7: Travel time changes on the facility
Period Scenario NB SB
V/C Speed (mph) Time (min) V/C Speed (mph) Time (min)
AM Peak Before 0.39 17.0 5.30 0.39 18.5 4.31
After 0.42 18.6 5.10 0.64 20.4 3.92
Difference 0.02 1.7 -0.20 0.25 1.9 -0.39
% Difference 6.00% 9.72% -3.77% 63.10% 10.00% -9.05%
PM Peak Before 0.50 18.5 4.33 0.43 16.2 6.60
After 0.54 20.3 3.94 0.45 17.6 6.68
Difference 0.04 1.8 -0.39 0.02 1.4 0.08
% Difference 8.91% 9.88% -9.01% 5.07% 8.47% 1.21%
Off Peak Before 0.21 18.5 4.33 0.20 18.5 4.31
After 0.22 20.3 3.94 0.32 20.4 3.92
Difference 0.01 1.8 -0.39 0.12 1.9 -0.39
% Difference 5.13% 9.88% -9.01% 58.64% 10.00% -9.05%
TABLE 45 Case Study 7: Volume changes on the facility
Period Direction Before After Difference %Difference
AM Peak NB 2,167 2,297 130 6.00%
SB 2,262 3,666 1,405 62.10%
TOT 4,428 5,963 1,535 34.65%
PM Peak NB 2,801 3,048 248 8.84%
SB 2,401 2,538 137 5.68%
TOT 5,202 5,586 384 7.38%
Off Peak NB 7,091 7,455 364 5.13%
SB 6,719 10,697 3,978 59.20%
TOT 13,811 18,152 4,341 31.43%
Total NB 12,059 12,800 741 6.15%
SB 11,382 16,901 5,519 48.48%
TOT 23,441 29,700 6,260 26.70%
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TABLE 46 Case Study 7: 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 12,150,900 381,266 31.9
PM Peak 15,259,400 517,865 29.5
Off Peak 37,204,700 1,176,500 31.6
Total 64,615,000 2,075,631 31.1 44,983,926 713,840,873 46,349,753
Difference -8,400 -3,331 0.0 -16,260 -224,008 -7,126
% Difference -0.01% -0.16% 0.15% -0.04% -0.03% -0.02%
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