Click for next page ( 49


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 48
48 CHAPTER 14 CASE STUDY 5: ACCESS MANAGEMENT Case Study 5 tests the impacts of converting a suburban effects of adding traffic signals to the rural unsignalized highway into a limited-access expressway. The specific loca- intersections. tion for this case study is a 10.1-mile-long section of State The free-flow speed for the entire length of the route USER'S GUIDE Route 169 between I-405 and SR 18 near Renton, Washing- was increased from 34 mph to 40 mph to account for ton (see Figure 11). the greater speeds possible with expressway operations. 14.1 APPLICATION 14.2 CASE STUDY RESULTS The stretch of SR 169 is a suburban highway with few sig- nalized intersections and frequent driveways to access fronting The NCHRP 25-21 methodology was used to compute the land uses. The access management project includes median impacts of the traffic-flow improvement on the 2020 base barriers the length of the expressway (thus enabling increased case trip tables by time period (AM peak, PM peak, and off speeds) with signalized intersections at median breaks to serve peak) and by mode (SOV, HOV, and transit). The revised trip fronting land uses and allow U-turns. The more frequent sig- tables were then reassigned to the improved network to deter- nalized intersections and the concentration of access at these mine the impact on VMT, VHT, and emissions. The results intersections result in less green time available for through traf- are summarized in Tables 36 through 38. fic on the expressway, thus reducing capacity. However, this reduced capacity is counterbalanced by increased speeds This case study illustrates the impacts of improving facility between intersections with the elimination of fronting access speed and capacity through access control of fronting devel- to the facility except at the signalized intersections. opment driveways and side streets. Unlike the earlier case SR 169 has two lanes in each direction. The section between studies, both peak-period and daily travel times are improved I-405 and 140th Avenue SE is an urban arterial with added by over 10 percent. Daily traffic on the facility is increased HOV lanes. The access management project was estimated 67 percent. to yield the following improvements: The net effect of the access control improvements is to increase regional VMT by less than 0.01 percent. However, The capacity of the rural portion of the route was reduced the traffic-flow smoothing effects of the project cause a reduc- from 1,500 vph/lane to 1,200 vph/lane to account for the tion in regional emissions of 0.02 to 0.04 percent.

OCR for page 48
49 Project USER'S GUIDE Figure 11. Case Study 5: SR-169 access management. TABLE 36 Case Study 5: 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 0.12 39.8 15.15 0.62 39.7 15.18 Difference 0.06 4.0 -2.04 0.33 4.0 -2.04 % Difference 82.61% 11.18% -11.87% 110.86% 11.20% -11.85% PM Peak Before 0.29 35.8 17.19 0.13 35.7 17.22 After 0.56 39.8 15.15 0.24 39.7 15.18 Difference 0.28 4.0 -2.04 0.12 4.0 -2.04 % Difference 95.12% 11.18% -11.87% 94.76% 11.20% -11.85% Off Peak Before 0.08 35.8 17.19 0.07 35.7 17.22 After 0.16 39.8 15.15 0.15 39.7 15.18 Difference 0.08 4.0 -2.04 0.07 4.0 -2.04 % Difference 92.60% 11.18% -11.87% 103.51% 11.20% -11.85% TABLE 37 Case Study 5: Volume changes on the facility Period Direction Before After Difference %Difference AM Peak EB 568 878 310 54.64% WB 2,517 4,492 1,975 78.48% TOT 3,085 5,370 2,286 74.09% PM Peak EB 2,464 4,063 1,599 64.91% WB 1,066 1,753 687 64.45% TOT 3,530 5,817 2,287 64.77% Off Peak EB 4,217 6,794 2,578 61.13% WB 3,728 6,354 2,626 70.45% TOT 7,944 13,148 5,204 65.50% Total EB 7,249 11,736 4,487 61.90% WB 7,311 12,599 5,288 72.34% TOT 14,559 24,335 9,776 67.14%

OCR for page 48
50 TABLE 38 Case Study 5: 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 12,152,800 381,263 31.9 PM Peak 15,260,400 517,202 29.5 Off Peak 37,211,700 1,179,000 31.6 Total 64,624,900 2,077,465 31.1 44,983,926 713,840,873 46,349,753 Difference 1,500 -1,497 0.0 -16,260 -224,008 -7,126 % Difference 0.00% -0.07% 0.07% -0.04% -0.03% -0.02% USER'S GUIDE