MEMORANDUM. Date: September 22, Don Skillingstad, Spokane Transit Authority. Yongliang Zhu, Lochner

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1 MEMORANDUM Date: September 22, 2014 To: Don Skillingstad, Spokane Transit Authority From: Yongliang Zhu, Lochner Re: Attachments: Median Flyer Stop Weave Analysis West Plains Transit Center IJR Project No.: 9715 Exhibit 1: HOV Access Ramp Exhibit Exhibit 2: Base Year Model Link Volume and Actual Traffic Count Comparison Exhibit 3: Weave Analysis HCS Reports Summary On August 8, 2014, at the West Plains Transit Center Kick-Off meeting, Mike Frucci (WSDOT) expressed his concern about buses being able to accelerate from a median flyer stop located immediately west of the I-90/SR 902 interchange and exit at the I-90/SR 904 interchange to the west. Mike recommended a weave analysis to confirm that the movement was possible before continuing to study that option. In response to WSDOT s request, Lochner conducted a weave analysis for the westbound I-90 segment between the proposed West Plains Transit Center median flyer stop and SR 904 off ramp, with the methodology defined by the 2010 Highway Capacity Manual, assuming 2040 as the design year. The analysis is summarized as follows: During the AM peak hour, the freeway operates at LOS B During the PM peak hour, the freeway operates at LOS C Median Flyer Stop Alternative The Medical Lake interchange is categorized as an urban interchange with a 70 mph design speed on I-90. The on-connection for the median flyer stop would have a total width of 24 and a maximum grade of 5% (See WSDOT Design Manual page ). For a left-side on-connection, WSDOT recommends a parallel on-connection, which adds a parallel lane long enough for the merging vehicle to accelerate in the lane and then merge with the through-traffic. This merge is similar to a lane change and the driver can use side- and rear-view mirrors to his or her advantage. A parallel on-connection consists of acceleration length, gap acceptance length, and taper, as shown below: 1

2 The length of the proposed on-connection is 4270, which includes: Acceleration length: La = 3045 (WSDOT DM page ), Gap Acceptance Length: Lg = 925 (WSDOT DM page ), and 300 taper. (WSDOT DM page ) See attached Exhibit 1 for details. During the design process, the ramp length will be adjusted to account for final profile and alignment to meet current design standards. Model Validation and Post Processing The traffic volumes for the weave analysis are taken from the Spokane Region Transportation Council (SRTC) 2040 model. Before the model being used to obtain the future traffic volumes, the preliminary checks are performed to ensure that the forecasting processes are suitable for this project. This check involved comparing the 2010 base year simulated link volumes with the actual traffic count data. A statistical measure of root-mean-square-error (RMSE) is calculated per NCHRP Report 765 Chapter 4.4. The calculation is summarized as follow: For the AM peak period, the average traffic volume for the selected links within the study area is 420 vph with a RMSE of 159. This results a traffic forecasting error of 38%, which is within the accuracy limit of 42% listed on NCHRP Report 765, page 81, Table September 09, 2014 hwlochner.com

3 For the PM peak period, the average traffic volume for the selected links within the study area is 468 vph with a RMSE of 153. This results a traffic forecasting error of 32%, which is close to the accuracy limit of 31% listed on NCHRP Report 765, page 81, Table 4-6. This preliminary check indicates that SRTC models are suitable for the future traffic forecasting for the study area and is also adequate for the weave analysis. The 2010 base year link volumes and actual traffic count data comparison is attached as Exhibit 2. To account for localized discrepancies between existing ground counts and model-generated volumes, a model postprocessing is utilized. This method is described as Factoring Procedure Difference Method in NCHRP 765 Chapter 6, which add the model growth increment (the difference between the 2010 and the 2040 model volumes) to the existing ground count traffic volumes. The weave analysis uses the adjusted 2040 peak hour traffic volumes coming out of the post-processing. Weave Analysis The weaving area on the westbound I-90 between the proposed West Plains Transit Center median bus lane and SR 904 off ramp is 4,360 feet long. It is considered a two-sided weave with a one-lane, left-sided on-ramp followed by a one-lane rightsided off-ramp. The traffic volumes are taken from the Spokane Region Transportation Council (SRTC) 2040 model and adjusted per NCHRP Special Report 765. The weave analyses were conducted for AM and PM peak hours for the design year They were summarized as follows: During the AM peak hour, the freeway weaving operates at LOS B with weaving segment density of 14.1 pc/mi/ln. During the PM peak hour, the freeway weaving operates at LOS C with weaving segment density of 21.5 pc/mi/ln. The detailed weaving reports are attached in Exhibit 3. Conclusion This analysis shows that a bus exiting the median flyer stop has approximately 4,360 feet after entering the freeway mainline, to change lanes and exit the freeway at SR 904. The section of I-90 between the proposed median flyer stop and the off-ramp to SR 904 is in a tangent and on level terrain. Based on these conditions and the volumes presented in the analysis, the weave distance provided, and shown in Exhibit 1, is adequate to safely make the maneuver in all weather conditions. 3

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5 2010 Base Model Link Volume vs Traffic Count Comparison Link No. Link AM PM V (forecast) C (count) V (forecast) C (count) 1 SR 902 EB On Ramp SR 902 EB Off Ramp SR 902 WB On Ramp SR 902 WB Off Ramp SR 902 Between EB and WB Ramps NB SR 902 Between EB and WB Ramps SB Westbow Blvd East of Aero Rd WB Westbow Blvd East of Aero Rd EB Aero Rd North of Westbow Blvd NB Aero Rd North of Westbow Blvd SB Aero Rd South of Westbow Blvd NB Aero Rd South of Westbow Blvd SB Hayford Rd East of Medical lake Rd EB Hayford Rd East of Medical lake Rd WB Medical Lake Rd North of Hayford Rd NB Medical Lake Rd North of Hayford Rd SB Medical Lake Rd South of Hayford Rd NB Medical Lake Rd South of Hayford Rd SB SR 904 Off Ramp Average Link Volume

6 Phone: HCS 2010: Freeway Weaving Release 6.50 Fax: Operational Analysis Analyst: Yong Zhu Agency/Co.: Lochner Date Performed: 8/15/2014 Analysis Time Period: AM peak Freeway/Dir of Travel: I-90 Westbound Weaving Location: Between SR904 and SR902 Analysis Year: 2040 Description: West Plains Transit Center Inputs Segment Type Freeway Weaving configuration Two-Sided Number of lanes, N 2 ln Weaving segment length, LS 4360 ft Freeway free-flow speed, FFS 70 mi/h Minimum segment speed, SMIN 15 mi/h Freeway maximum capacity, cifl 2400 pc/h/ln Terrain type Level Grade 0.00 % Length 0.00 mi Conversion to pc/h Under Base Conditions Volume Components VFF VRF VFR VRR Volume, V veh/h Peak hour factor, PHF Peak 15-min volume, v Trucks and buses % Recreational vehicles % Trucks and buses PCE, ET Recreational vehicle PCE, ER Heavy vehicle adjustment, fhv Driver population adjustment, fp Flow rate, v pc/h Volume ratio, VR Configuration Characteristics Number of maneuver lanes, NWL 0 ln Interchange density, ID 0.5 int/mi Minimum RF lane changes, LCRF 0 lc/pc Minimum FR lane changes, LCFR 0 lc/pc Minimum RR lane changes, LCRR 2 lc/pc Minimum weaving lane changes, LCMIN 26 lc/h Weaving lane changes, LCW 163 lc/h Non-weaving vehicle index, INW 400 Non-weaving lane change, LCNW 2356 lc/h Total lane changes, LCALL 2519 lc/h Weaving and Non-Weaving Speeds Weaving intensity factor, W 0.147

7 Average weaving speed, SW 63.0 mi/h Average non-weaving speed, SNW 65.4 mi/h Weaving Segment Speed, Density, Level of Service and Capacity Weaving segment speed, S 65.4 mi/h Weaving segment density, D 14.1 pc/mi/ln Level of service, LOS B Weaving segment v/c ratio Weaving segment flow rate, v 1680 veh/h Weaving segment capacity, cw 4164 veh/h Limitations on Weaving Segments If limit reached, see note. Minimum Maximum Actual Note Weaving length (ft) a,b Maximum Analyzed Density-based capacty, c ciwl (pc/h/ln) Maximum Analyzed v/c ratio d Notes: a. In weaving segments shorter than 300 ft, weaving vehicles are assumed to make only necessary lane changes. b. Weaving segments longer than the calculated maximum length should be treated as isolated merge and diverge areas using the procedures of Chapter 13, "Freeway Merge and Diverge Segments." c. The density-based capacity exceeds the capacity of a basic freeway segment, under equivalent ideal conditions. d. Volumes exceed the weaving segment capacity. The level of service is F.

8 Phone: HCS 2010: Freeway Weaving Release 6.50 Fax: Operational Analysis Analyst: Yong Zhu Agency/Co.: Lochner Date Performed: 8/15/2014 Analysis Time Period: PM peak Freeway/Dir of Travel: I-90 Westbound Weaving Location: Between SR904 and SR902 Analysis Year: 2040 Description: West Plains Transit Center Inputs Segment Type Freeway Weaving configuration Two-Sided Number of lanes, N 2 ln Weaving segment length, LS 4360 ft Freeway free-flow speed, FFS 70 mi/h Minimum segment speed, SMIN 15 mi/h Freeway maximum capacity, cifl 2400 pc/h/ln Terrain type Level Grade 0.00 % Length 0.00 mi Conversion to pc/h Under Base Conditions Volume Components VFF VRF VFR VRR Volume, V veh/h Peak hour factor, PHF Peak 15-min volume, v Trucks and buses % Recreational vehicles % Trucks and buses PCE, ET Recreational vehicle PCE, ER Heavy vehicle adjustment, fhv Driver population adjustment, fp Flow rate, v pc/h Volume ratio, VR Configuration Characteristics Number of maneuver lanes, NWL 0 ln Interchange density, ID 0.5 int/mi Minimum RF lane changes, LCRF 0 lc/pc Minimum FR lane changes, LCFR 0 lc/pc Minimum RR lane changes, LCRR 2 lc/pc Minimum weaving lane changes, LCMIN 26 lc/h Weaving lane changes, LCW 163 lc/h Non-weaving vehicle index, INW 591 Non-weaving lane change, LCNW 2537 lc/h Total lane changes, LCALL 2700 lc/h Weaving and Non-Weaving Speeds Weaving intensity factor, W 0.155

9 Average weaving speed, SW 62.6 mi/h Average non-weaving speed, SNW 63.3 mi/h Weaving Segment Speed, Density, Level of Service and Capacity Weaving segment speed, S 63.3 mi/h Weaving segment density, D 21.5 pc/mi/ln Level of service, LOS C Weaving segment v/c ratio Weaving segment flow rate, v 2479 veh/h Weaving segment capacity, cw 4167 veh/h Limitations on Weaving Segments If limit reached, see note. Minimum Maximum Actual Note Weaving length (ft) a,b Maximum Analyzed Density-based capacty, c ciwl (pc/h/ln) Maximum Analyzed v/c ratio d Notes: a. In weaving segments shorter than 300 ft, weaving vehicles are assumed to make only necessary lane changes. b. Weaving segments longer than the calculated maximum length should be treated as isolated merge and diverge areas using the procedures of Chapter 13, "Freeway Merge and Diverge Segments." c. The density-based capacity exceeds the capacity of a basic freeway segment, under equivalent ideal conditions. d. Volumes exceed the weaving segment capacity. The level of service is F.