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 1420-12). 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
The length of the proposed on-connection is 4270, which includes: Acceleration length: La = 3045 (WSDOT DM page 1420-14), Gap Acceptance Length: Lg = 925 (WSDOT DM page 1420-15), and 300 taper. (WSDOT DM page 1420-13) 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 4-6. 2 September 09, 2014 hwlochner.com
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 2040. 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
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 503 493 552 426 2 SR 902 EB Off Ramp 311 144 198 196 3 SR 902 WB On Ramp 161 140 388 198 4 SR 902 WB Off Ramp 491 368 477 400 5 SR 902 Between EB and WB Ramps NB 464 283 436 282 6 SR 902 Between EB and WB Ramps SB 642 537 717 555 7 Westbow Blvd East of Aero Rd WB 291 132 316 107 8 Westbow Blvd East of Aero Rd EB 234 85 276 92 9 Aero Rd North of Westbow Blvd NB 487 440 584 417 10 Aero Rd North of Westbow Blvd SB 473 330 511 442 11 Aero Rd South of Westbow Blvd NB 196 121 268 186 12 Aero Rd South of Westbow Blvd SB 239 203 236 201 13 Hayford Rd East of Medical lake Rd EB 380 190 305 219 14 Hayford Rd East of Medical lake Rd WB 190 115 467 287 15 Medical Lake Rd North of Hayford Rd NB 410 291 426 334 16 Medical Lake Rd North of Hayford Rd SB 448 393 456 343 17 Medical Lake Rd South of Hayford Rd NB 675 396 601 445 18 Medical Lake Rd South of Hayford Rd SB 523 427 794 518 19 SR 904 Off Ramp 853 443 886 652 Average Link Volume 420 468
Phone: E-mail: 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 861 0 705 8 veh/h Peak hour factor, PHF 0.92 0.92 0.92 0.92 Peak 15-min volume, v15 234 0 192 2 Trucks and buses 20 0 10 100 % Recreational vehicles 0 0 0 0 % Trucks and buses PCE, ET 1.5 1.5 1.5 1.5 Recreational vehicle PCE, ER 1.2 1.2 1.2 1.2 Heavy vehicle adjustment, fhv 0.909 1.000 0.952 0.667 Driver population adjustment, fp 1.00 1.00 1.00 1.00 Flow rate, v 1029 0 805 13 pc/h Volume ratio, VR 0.007 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
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 0.403 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) 300 5793 4360 a,b Maximum Analyzed Density-based capacty, 2400 2290 c ciwl (pc/h/ln) Maximum Analyzed v/c ratio 1.00 0.403 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.
Phone: E-mail: 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 1318 0 996 8 veh/h Peak hour factor, PHF 0.92 0.92 0.92 0.92 Peak 15-min volume, v15 358 0 271 2 Trucks and buses 20 0 10 100 % Recreational vehicles 0 0 0 0 % Trucks and buses PCE, ET 1.5 1.5 1.5 1.5 Recreational vehicle PCE, ER 1.2 1.2 1.2 1.2 Heavy vehicle adjustment, fhv 0.909 1.000 0.952 0.667 Driver population adjustment, fp 1.00 1.00 1.00 1.00 Flow rate, v 1576 0 1137 13 pc/h Volume ratio, VR 0.005 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
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 0.595 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) 300 5772 4360 a,b Maximum Analyzed Density-based capacty, 2400 2292 c ciwl (pc/h/ln) Maximum Analyzed v/c ratio 1.00 0.595 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.