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Home My WebLink AboutSD-24-04 - Supplemental - 0760 Shelburne Road (9)Page 1 TECHNICAL MEMORANDUM Project: Bourne – Shelburne Rd & Swift St, South Burlington Date: January 12, 2023, rev. March 23, 2023 By: Roger Dickinson, PE Subject: Traffic Impact Assessment Introduction The Bourne redevelopment project (hereafter referred to as the Project) is located in the southeast corner of the intersection of Shelburne Road (US Route 7) and Swift Street in South Burlington. The Project includes consolidating three presently separate parcels into one and redeveloping the resulting parcel. The existing parcels are: #760 Shelburne Rd located on the corner - formerly Bourne’s Convenience Store; #764 Shelburne Rd - formerly the Pizza Hut restaurant, and; #31 Swift St - Bourne’s Service Center. Access to the above parcels are provided by four existing driveways; two on the east side of Shelburne Rd plus two on the south side of Swift St. This Project will reduce the total number to two; one each on Shelburne Rd and Swift St. This traffic impact assessment (TIA) examines existing and future traffic congestion conditions on the adjacent highway network in the vicinity of this Project, and analyzes the probable impacts that this Project will have on those conditions. The results of the requested analyses are presented in the following sections. Adjacent Street Network Shelburne Rd is a major arterial highway on the state highway system. Shelburne Rd along the Project’s frontage includes three northbound lanes (two for through traffic and one for right-turns onto Swift St and I-189) and two southbound lanes (for through traffic); separated by a two-way left-turn lane. Sidewalks are provided on both sides of Shelburne Rd, with a signalized crosswalk located at the Queen City Park Rd intersection just south of the Project. Swift St is a major collector local street providing one travel lane in each direction. Swift St widens along the Project’s frontage to provide separate left- and right-turn lanes at its intersection with Shelburne Rd. A sidewalk is provided along the south side of Swift St; with a crosswalk located at its intersection with Shelburne Rd. This crosswalk was signalized as part of the Vermont Agency of Transportation’s (VTrans) recently completed Shelburne Rd traffic signal replacement project. Page 2 Background Traffic Volumes Background traffic volumes on Shelburne Rd and Swift St were obtained from a 12-hour turning movement count performed at their intersection by VTrans on June 27-28, 2016. The observed pm peak hour volumes from the above turning movement count were adjusted to estimated design hour volumes (DHV) for year 2029 (project completion + 5 years) by examining data from VTrans’ Continuous Traffic Counter Station D099, located nearby on I-189. A DHV adjustment factor of +8.2% was calculated from that data. Additionally, background traffic growth factors of 0.0% (2016 to 2024) and 2.5% (2024 to 2029)1 were estimated. The resulting projected 2029 background design hour volumes (representing the No-Build analysis scenarios) at the Shelburne Rd / Swift St intersection are shown in Figure 1. Figure 1 - 2029 No-Build DHV Project-Generated Traffic This Project is located in Zone 1 of South Burlington’s Traffic Overlay District, which permits a maximum pm peak hour trip generation of 15 vehicle trip ends per hour (vte/hr) per 40,000 sf of lot size. The three lots included in this Project have a total lot size of 60,700 sf; for which the maximum permitted pm peak hour trip generation equals 22.76 vte/hr. Morning (am) peak hour trips are not limited by the Traffic Overlay District. The Traffic Overlay District permits the maximum pm peak hour trip generation to be adjusted to match the existing peak hour trip generation of the uses presently authorized and operating on the site. Thus, with one exception, this Project has available to it, for the purpose of establishing its “traffic budget”, the pm peak hour trips which are generated by the existing uses on the three lots. The one exception is 1 Continuous Traffic Counter Report (The Redbook) Based on 2021 Traffic Data, Vermont Agency of Transportation, May 2022 1837 226  417 202  1810 214 Shelburne Rd Swift St Shelburne Rd Page 3 the former Pizza Hut restaurant, which has been closed for an extended period of time, and thus is no longer an authorized and operating use. Table 1 presents the estimated peak hour trips for both the existing uses on the three parcels and for this Project. The estimated peak hour trips were calculated by using trip generation rates compiled by the Institute of Transportation Engineers (ITE) in Trip Generation2, except as noted above for the former Pizza Hut restaurant. Table 1 - Weekday Trip Generation ITE Land-Use Category Size AM Peak Hour PM Peak Hour Enter Exit Total Enter Exit Total Existing #712 – Small Office Building 4,260 sf 6 1 7 3 6 9 #943 – Automobile Parts & Service Center 1,500 sf 2 1 3 1 2 3 #945 – Convenience Store/Gas Station (2-8 vfp) 2,100 sf 43 42 85 51 51 102 #932 – High-Turnover (Sit Down) Restaurant a --------6 4 10 Total Trips 51 44 95 61 63 124 Proposed #220 – Multifamily Housing (Low-Rise)30 units 3 9 12 9 6 15 #822 – Strip Retail Plaza (<40 ksf)3,200 sf 8 6 14 17 18 35 #912 – Drive-In Bank 3,350 sf 19 14 33 35 35 70 Total Trips 30 29 59 61 59 120 a Calculated by applying the Traffic Overlay District Zone 1 permitted trip generation of 15 vte/hr/40,000 sf to Pizza Hut’s 0.61 acre lot size. Figure 2 presents the directional distribution of the proposed Project-generated pm peak hour trips. The overall distribution was estimated using existing traffic patterns entering and exiting the Shelburne Rd / Swift St intersection. The directional splits of traffic entering and exiting the Project at its two proposed driveways onto Shelburne Rd and Swift St were then estimated using engineering judgement; with consideration being given to the high volumes of northbound traffic and queueing which occurs on Shelburne Rd in this immediate area during the pm peak period. Combining the project-generated trips with the No-Build volumes provides the 2029 Build design hour volumes shown in Figure 3. 2 Trip Generation, Institute of Transportation Engineers, 11th Edition Page 4 Figure 2 – Proposed PM Peak Hour Trips Figure 3 - 2029 Build PM DHV Traffic Congestion Levels of service (LOS) at intersections are determined by the average control delay; measured in seconds per vehicle. The methodology for analyzing LOS is established by the Highway Capacity Manual (HCM).3 Table 2 summarizes the LOS delay thresholds for intersections. 3 Highway Capacity Manual, Transportation Research Board, 6th Edition 6 21  22  24 21 8  6 45 6 24 6 Enter 61 6 Exit 59 2 Total 120  26 Shelburne Rd Shelburne Rd Swift St Bourne Access PM Peak Hour Trips Bourne Access 1837 226  417 419 574 202 21 8  1810 214 45 6 2033 6  6 2  2018 26 Shelburne Rd Shelburne Rd Swift St Bourne Access Bourne Access Page 5 Table 2 - Intersection Level of Service Criteria LOS Avg. Delaya LOS Avg. Delaya Unsignalized Signalized Unsignalized Signalized A B C ≤10 ≤15 ≤25 ≤10 ≤20 ≤35 D E F ≤35 ≤50 >50 ≤55 ≤80 >80 a seconds per vehicle Table 3 presents the results of intersection capacity analyses performed at the Shelburne Rd / Swift St intersection and at this Project’s two proposed accesses onto Shelburne Rd and Swift St. All analyses were performed using Synchro v.11 software. Detailed analysis reports are enclosed in Appendix A. Table 3 - Intersection Levels of Service Intersection / Approach 2029 PM Build LOS Delay V/C 95% Q Shelburne Rd / Swift St Swift St WB L Swift St WB R Shelburne Rd NB T Shelburne Rd NB R Shelburne Rd SB L Shelburne Rd ST T Overall D D D B D A C 47.8 40.6 38.6 11.7 47.3 7.3 26.2 0.75 0.83 0.96 0.25 0.77 0.70 259’ 398’ 840’ 49’ 274’ 398’ Shelburne Rd / Project Access Project Access WB L/R Shelburne Rd SB L F E 107.6 38.3 0.19 0.05 25’ 25’ Swift St / Project Access Project Access NB L/R Swift St WB L C A 21.3 8.3 0.20 0.01 25’ 0’ The results of the intersection capacity analyses results indicate that the Shelburne Rd / Swift St intersection will operate at LOS C. Traffic exiting the Project at its access onto Swift St will also experience LOS C. However, traffic exiting the Project at its Shelburne Rd access will experience long delays (LOS F) during future pm peak hour traffic conditions. Vehicles desiring to exit onto Shelburne Rd at that location will be effectively blocked by northbound Shelburne Rd queuing during peak traffic periods. Access Management As noted earlier, this Project will reduce the number of accesses from four to two. The four existing accesses, and a description of how they will be modified, include: Page 6 -A 40 ft wide access onto Shelburne Rd serving the former convenience store, located 89 ft4 south of the northbound stop bar on Shelburne Rd at Swift St. This access will be closed. -A 40 ft wide access onto Shelburne Rd serving the former Pizza Hut restaurant, located 192 ft south of the above northbound stop bar. The curb cut for this access straddles the property line with the adjacent Koto restaurant, with the resulting curb cut on Shelburne Rd being 80 ft long. This access will be replaced by a new 24 ft wide access located 178 ft south of the northbound stop bar on Shelburne Rd. This new access will be physically separate from the one serving the Koto restaurant. -A 30 ft wide access onto Swift St serving the former convenience store, located 58 ft east of the westbound stop bar on Swift St at Shelburne Rd. This access will be closed. -A 30 ft wide access onto Swift St serving Bourne’s Service Center, located 148 ft east of the above westbound stop bar. This access will be replaced by a new 24 ft wide access located 193 ft east of the westbound stop bar on Swift St. The above proposed accesses have been located to maximize the spacing between them and the Shelburne Rd / Swift St intersection as much as possible. Where the proposed accesses overlap with existing ones, the existing accesses will be completely removed. This Project also includes provisions for a future interior connection with the Koto restaurant parcel to the south so that traffic traveling between the two parcels will not be required to use Shelburne Rd. The proposed accesses to this Project will improve access management on both Shelburne Rd and Swift St; providing reduced vehicular and pedestrian conflicts, a corresponding improvement in future traffic safety conditions, and more efficient traffic flow. Conclusions The results of the above examination of future traffic conditions with the proposed Project indicate the following: -That its pm peak hour trip generation will be slightly less than that of the existing uses on the three parcels being consolidated and redeveloped. -Future traffic congestion conditions at the Shelburne Rd / Swift St intersection and this Project’s proposed access onto Swift St will be LOS C. -Traffic exiting this Project’s proposed access onto Shelburne Rd will experience long delays and poor levels of service (LOS F) during future peak hour traffic conditions. Knowing this, Project- generated exiting trips will instead gravitate to exit via Swift St, where they will be able to turn onto Shelburne Rd at a signalized intersection. 4 All distances are to the center of the access. NOTE: The traffic calculations and associated Traffic Impact Assessment (Last Revised 3/23/2023) are based on the previous iteration of the proposed project (for conservative purposes) including 30 units of Low-Rise Multifamily Housing (ITE Land Use #220), 3200 SF of Strip Retail Plaza (ITE Land Use #822) and 3350 SF of Drive-In Bank (ITE Land Use #912). The proposed project, included in this application, will actually generate fewer trips than the prior iteration as the previous drive-in bank has been replaced with a Walk-In Bank (ITE Land Use #911) which has a lower trip generation. Regardless, both the prior and current iterations of the project will slightly reduce the PM Peak Hour trips from the site’s existing/previous uses, the Shelburne Road/Swift Street and project’s Swift Street access will be LOS C, and exiting traffic from the project site will gravitate to the Swift Street access due to the delays associated with exiting onto Shelburne Road. APPENDIX A Intersection Capacity Analyses HCM 6th Signalized Intersection Summary 2029 PM DHV 3: Shelburne Rd & Swift St Build 2029 PM Build rev.syn 03/23/2023 Page 1 Movement WBL WBR NBT NBR SBL SBT Lane Configurations Traffic Volume (veh/h)202 417 1810 214 226 1837 Future Volume (veh/h)202 417 1810 214 226 1837 Initial Q (Qb), veh 0 0 0 0 0 0 Ped-Bike Adj(A_pbT)1.00 1.00 1.00 1.00 Parking Bus, Adj 1.00 1.00 1.00 1.00 1.00 1.00 Work Zone On Approach No No No Adj Sat Flow, veh/h/ln 1826 1826 1826 1826 1826 1826 Adj Flow Rate, veh/h 202 417 1810 214 226 1837 Peak Hour Factor 1.00 1.00 1.00 1.00 1.00 1.00 Percent Heavy Veh, %5 5 5 5 5 5 Cap, veh/h 271 502 1882 839 293 2621 Arrive On Green 0.16 0.16 0.54 0.54 0.17 0.76 Sat Flow, veh/h 1739 1547 3561 1547 1739 3561 Grp Volume(v), veh/h 202 417 1810 214 226 1837 Grp Sat Flow(s),veh/h/ln 1739 1547 1735 1547 1739 1735 Q Serve(g_s), s 10.0 14.0 44.9 6.6 11.2 24.8 Cycle Q Clear(g_c), s 10.0 14.0 44.9 6.6 11.2 24.8 Prop In Lane 1.00 1.00 1.00 1.00 Lane Grp Cap(c), veh/h 271 502 1882 839 293 2621 V/C Ratio(X)0.75 0.83 0.96 0.25 0.77 0.70 Avail Cap(c_a), veh/h 271 502 1882 839 309 2621 HCM Platoon Ratio 1.00 1.00 1.00 1.00 1.00 1.00 Upstream Filter(I)1.00 1.00 1.00 1.00 1.00 1.00 Uniform Delay (d), s/veh 36.3 28.1 19.7 10.9 35.7 5.7 Incr Delay (d2), s/veh 11.5 12.5 18.9 0.7 11.6 1.6 Initial Q Delay(d3),s/veh 0.0 0.0 0.0 0.0 0.0 0.0 %ile BackOfQ(50%),veh/ln 5.0 9.7 21.1 2.3 5.6 6.9 Unsig. Movement Delay, s/veh LnGrp Delay(d),s/veh 47.8 40.6 38.6 11.7 47.3 7.3 LnGrp LOS D D D B D A Approach Vol, veh/h 619 2024 2063 Approach Delay, s/veh 43.0 35.8 11.7 Approach LOS D D B Timer - Assigned Phs 1 2 6 8 Phs Duration (G+Y+Rc), s 19.2 52.8 72.0 18.0 Change Period (Y+Rc), s 6.0 6.0 6.0 6.0 Max Green Setting (Gmax), s 14.0 46.0 66.0 12.0 Max Q Clear Time (g_c+I1), s 13.2 46.9 26.8 16.0 Green Ext Time (p_c), s 0.1 0.0 22.7 0.0 Intersection Summary HCM 6th Ctrl Delay 26.2 HCM 6th LOS C Notes User approved pedestrian interval to be less than phase max green. Queues 2029 PM DHV 3: Shelburne Rd & Swift St Build 2029 PM Build rev.syn 03/23/2023 Page 1 Lane Group WBL WBR NBT NBR SBL SBT Lane Group Flow (vph)202 417 1810 214 226 1837 v/c Ratio 0.77 0.73 0.97 0.23 0.77 0.70 Control Delay 60.3 32.7 43.6 2.9 55.8 7.6 Queue Delay 0.0 0.0 0.0 0.0 0.0 0.0 Total Delay 60.3 32.7 43.6 2.9 55.8 7.6 Queue Length 50th (ft)111 194 503 6 123 230 Queue Length 95th (ft)#259 #398 #840 49 #274 398 Internal Link Dist (ft)500 730 375 Turn Bay Length (ft)125 225 175 Base Capacity (vph)267 582 1865 922 305 2608 Starvation Cap Reductn 0 0 0 0 0 0 Spillback Cap Reductn 0 0 0 0 0 0 Storage Cap Reductn 0 0 0 0 0 0 Reduced v/c Ratio 0.76 0.72 0.97 0.23 0.74 0.70 Intersection Summary # 95th percentile volume exceeds capacity, queue may be longer. Queue shown is maximum after two cycles. HCM 6th TWSC 2029 PM DHV 5: Shelburne Rd & Bourne Build 2029 PM Build rev.syn 03/23/2023 Page 1 Intersection Int Delay, s/veh 0.3 Movement WBL WBR NBT NBR SBL SBT Lane Configurations Traffic Vol, veh/h 2 6 2018 26 6 2033 Future Vol, veh/h 2 6 2018 26 6 2033 Conflicting Peds, #/hr 0 0 0 0 0 0 Sign Control Stop Stop Free Free Free Free RT Channelized -None -None -None Storage Length 0 ---0 - Veh in Median Storage, #0 -0 --0 Grade, %0 -0 --0 Peak Hour Factor 100 100 100 100 100 100 Heavy Vehicles, %5 5 5 5 5 5 Mvmt Flow 2 6 2018 26 6 2033 Major/Minor Minor1 Major1 Major2 Conflicting Flow All 3060 1022 0 0 2044 0 Stage 1 2031 ----- Stage 2 1029 ----- Critical Hdwy 6.35 7.2 --5.4 - Critical Hdwy Stg 1 6.7 ----- Critical Hdwy Stg 2 5.9 ----- Follow-up Hdwy 3.7 3.95 --3.15 - Pot Cap-1 Maneuver 14 196 --114 - Stage 1 53 ----- Stage 2 292 ----- Platoon blocked, %--- Mov Cap-1 Maneuver 13 196 --114 - Mov Cap-2 Maneuver 13 ----- Stage 1 53 ----- Stage 2 277 ----- Approach WB NB SB HCM Control Delay, s 107.6 0 0.1 HCM LOS F Minor Lane/Major Mvmt NBT NBRWBLn1 SBL SBT Capacity (veh/h)--43 114 - HCM Lane V/C Ratio --0.186 0.053 - HCM Control Delay (s)--107.6 38.3 - HCM Lane LOS --F E - HCM 95th %tile Q(veh)--0.7 0.2 - HCM 6th TWSC 2029 PM DHV 7: Bourne & Swift St Build 2029 PM Build rev.syn 03/23/2023 Page 2 Intersection Int Delay, s/veh 1.1 Movement EBT EBR WBL WBT NBL NBR Lane Configurations Traffic Vol, veh/h 417 21 8 570 49 6 Future Vol, veh/h 417 21 8 570 49 6 Conflicting Peds, #/hr 0 0 0 0 0 0 Sign Control Free Free Free Free Stop Stop RT Channelized -None -None -None Storage Length ----0 - Veh in Median Storage, #0 --0 0 - Grade, %0 --0 0 - Peak Hour Factor 100 100 100 100 100 100 Heavy Vehicles, %5 5 5 5 5 5 Mvmt Flow 417 21 8 570 49 6 Major/Minor Major1 Major2 Minor1 Conflicting Flow All 0 0 438 0 1014 428 Stage 1 ----428 - Stage 2 ----586 - Critical Hdwy --4.15 -6.45 6.25 Critical Hdwy Stg 1 ----5.45 - Critical Hdwy Stg 2 ----5.45 - Follow-up Hdwy --2.245 -3.545 3.345 Pot Cap-1 Maneuver --1106 -261 620 Stage 1 ----651 - Stage 2 ----550 - Platoon blocked, %--- Mov Cap-1 Maneuver --1106 -258 620 Mov Cap-2 Maneuver ----258 - Stage 1 ----651 - Stage 2 ----544 - Approach EB WB NB HCM Control Delay, s 0 0.1 21.3 HCM LOS C Minor Lane/Major Mvmt NBLn1 EBT EBR WBL WBT Capacity (veh/h)276 --1106 - HCM Lane V/C Ratio 0.199 --0.007 - HCM Control Delay (s)21.3 --8.3 0 HCM Lane LOS C --A A HCM 95th %tile Q(veh)0.7 --0 -