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CHAPTER 15
CASE STUDY 6: INTERSECTION CHANNELIZATION
Case Study 6 consists of the addition of left-turn and right- 15.2 CASE STUDY RESULTS
turn lanes to all four approaches of an urban intersection at
Martin Luther King Jr. Way and Rainer Avenue in Seattle (see The NCHRP 25-21 methodology was used to compute the
USER'S GUIDE
Figure 12). impacts of the traffic-flow improvement on the 2020 base
case trip tables by time period (AM peak, PM peak, and off
peak) and by mode (SOV, HOV, and transit). The revised trip
15.1 APPLICATION
tables were then reassigned to the improved network to deter-
The addition of left-turn and right-turn lanes in the case mine the impact on VMT, VHT, and emissions. The results
study were coded as a 20-percent increase in the capacity on are summarized in Tables 39 through 43.
each approach. Before the improvement, all the approaches This case study shows the impacts of intersection chan-
to the intersection had two lanes and a capacity of 1,300 vph nelization improvements at an uncongested intersection. The
other than the northbound approach, which had a capacity of channelization improvements result in travel time improve-
1,400 vph. After a 20-percent increase in capacity, the north- ments of below the threshold of detectability for the method-
bound approach has a capacity of 1,650 vph, and all the other ology. The result is no change in predicted traffic volumes
approaches have a capacity of 1,550 vph, while the speed and for the intersection, no predicted changes in regional VMT,
number of lanes is unchanged. and no predicted changes in regional emissions.
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Project
USER'S GUIDE
Figure 12. Case Study 6: Intersection of MLK Jr. Way and Rainer Avenue in Seattle.
TABLE 39 Case Study 6: North/south 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 0.04 31.4 2.55 0.04 31.4 2.55
After 0.03 31.4 2.55 0.03 31.4 2.55
Difference 0.00 0.0 0.00 0.00 0.0 0.00
% Difference -9.68% 0.00% 0.00% -8.92% 0.00% 0.00%
PM Peak Before 0.05 31.4 2.55 0.05 31.4 2.55
After 0.05 31.4 2.55 0.04 31.4 2.55
Difference 0.00 0.0 0.00 0.00 0.0 0.00
% Difference -8.59% 0.00% 0.00% -7.07% 0.00% 0.00%
Off Peak Before 0.02 31.4 2.55 0.02 31.4 2.55
After 0.02 31.4 2.55 0.02 31.4 2.55
Difference 0.00 0.0 0.00 0.00 0.0 0.00
% Difference -9.01% 0.00% 0.00% -7.59% 0.00% 0.00%
TABLE 40 Case Study 6: East/west 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 31.9 2.40 0.28 32.0 2.40
After 0.09 31.9 2.40 0.26 32.0 2.40
Difference -0.01 0.0 0.00 -0.02 0.0 0.00
% Difference -8.04% 0.00% 0.00% -8.21% 0.00% 0.00%
PM Peak Before 0.32 31.9 2.40 0.17 32.0 2.40
After 0.30 31.9 2.40 0.15 32.0 2.40
Difference -0.02 0.0 0.00 -0.01 0.0 0.00
% Difference -7.66% 0.00% 0.00% -8.31% 0.00% 0.00%
Off Peak Before 0.10 31.9 2.40 0.09 32.0 2.40
After 0.10 31.9 2.40 0.09 32.0 2.40
Difference -0.01 0.0 0.00 -0.01 0.0 0.00
% Difference -7.87% 0.00% 0.00% -8.24% 0.00% 0.00%
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TABLE 41 Case Study 6: North/south volume changes on the
facility
Period Direction Before After Difference %Difference
AM Peak NB 302 302 0 0.00%
SB 286 286 0 0.00%
TOT 588 588 0 0.00%
PM Peak NB 446 446 0 0.00%
SB 373 373 0 0.00%
TOT 819 819 0 0.00%
Off Peak NB 1,153 1,153 0 0.00%
SB 943 943 0 0.00%
TOT 2,096 2,096 0 0.00%
Total NB 1,901 1,901 0 0.00%
SB 1,601 1,601 0 0.00%
TOT 3,502 3,502 0 0.00%
USER'S GUIDE
TABLE 42 Case Study 6: East/west volume changes on the
facility
Period Direction Before After Difference %Difference
AM Peak EB 799 799 0 0.00%
WB 2,192 2,192 0 0.00%
TOT 2,991 2,991 0 0.00%
PM Peak EB 2,522 2,522 0 0.00%
WB 1,298 1,298 0 0.00%
TOT 3,820 3,820 0 0.00%
Off Peak EB 4,880 4,880 0 0.00%
WB 4,446 4,446 0 0.00%
TOT 9,326 9,326 0 0.00%
Total EB 8,201 8,201 0 0.00%
WB 7,935 7,935 0 0.00%
TOT 16,136 16,136 0 0.00%
TABLE 43 Case Study 6: 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%
