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HomeMy WebLinkAbout32_ParkingGarageAccessDepartureRequestLetter_10182021 MARVIN & ASSOCIATES 1300 N. Transtech Way Billings, MT 59102 Mailing Address: P.O. Box 80785 Billings, MT 59108-0785 Phone: 406-655-4550 FAX: 406-655-4991 Page 1 HomeBase Partners 20 North Tracy Avenue Bozeman, MT 59715 September 20, 2021 Re: North Central Block 4 Lot 1A Parking Garage Access Departure Request This letter and attachments concern the Departure Request for location of a parking garage access on Villard Street for the propose parking garage to be built on Block 4 Lot 1A as part of the North Central Development in Bozeman. Specifically, this letter provides the traffic analysis items requested in a Memorandum from Karl Johnson dated September 8, 2021. Items a. through e. under “BMC 38.400.090 Access” within that memorandum are addressed within the following narratives: a. Traffic Volumes. The original Master Plan Traffic Impact Study (TIS) illustrated the traffic volumes for parking garages in Figure 11 (attached). Even though some of the parking garage locations were changed in subsequent TIS updates, the traffic volumes for the subject garage accesses were not affected and have not changed. The alley access to the garage would be closer to Beall Street and the alley access would attract some of the trips entering the site to and from the north on Willson Avenue and trips accessing the site on Beall Street. It would be counter intuitive for traffic to enter and exit the alley on Villard Street to use the alley access near Beall Street. b. Turning Movements. Left-turn conflicts involving concurrent movements from both the north alley and the proposed access would be extremely rare. However, when they do occur the vehicle paths would not overlap (see attached figure). Additionally, and most importantly, it would take both vehicles approximately 5.0 seconds from a stop condition to arrive at the point of conflict. Since both vehicles would be stopped or at least beginning their intended maneuvers and there is an unimpeded line of sight between both vehicles, there would ample time to avoid a collision. The attached figure also illustrates the more critical left-turn conflict involving two vehicles executing left-turn maneuvers from Villard Street into the alley and the garage accesses. In this case, both vehicles would be moving in opposite directions with little time to avoid a collision if their paths were to cross. It is seen in the attached figure that there would be no path overlap conflicts and the MARVIN & ASSOCIATES 1300 N. Transtech Way Billings, MT 59102 Mailing Address: P.O. Box 80785 Billings, MT 59108-0785 Phone: 406-655-4550 FAX: 406-655-4991 Page 2 concurrent movements would actually be safer than if the alley and the access were in direct alignment. c. Traffic Controls. The third attachment to this letter depicts projected future traffic volumes at the garage access and at the adjacent intersection of Willson Avenue and Villard Street. Capacity calculations for these two intersections were completed for the highest delay period in the peak PM hour (attached). It was determined that the worst level of service (LOS) would be “B” on both Villard Street approaches to Willson Avenue. The calculated maximum vehicle queues were one vehicle on both Villard Street approaches and for the northbound left-turn movement on Willson Avenue. d. Sight Distance Safety Analysis. The fourth attachment illustrates both eastbound and westbound sight distance calculations for the proposed access movements. The new street section would not have designated parking on the south side of Villard Street. The remaining section of Villard Street west of the alley does not have curb and gutter and is too narrow for parking. A vehicle sometimes parks on the south side of the street near a tree in the southeast corner of Grand Avenue and Villard Street. Villard Street is not stop controlled at its intersection with Grand Avenue and therefore eastbound through traffic on Villard could conflict with access egress movements. The available sight distance from the proposed access to oncoming eastbound traffic on Villard street was scaled at a distance greater than 250 feet, which is well beyond 155’ required for stopping sight distance. Left-turn movements from the proposed access could have potential conflicts with westbound traffic on Villard Street. Since Villard Street is stop-controlled, the westbound thru-movement vehicles from the westbound Villard Street approach would need to accelerate from a stop condition. Northbound left and southbound right movements from Willson Avenue onto Villard Street could also conflict with left-turn egress access movements. Because of the stop controlled intersection all conflict vehicles would have varying speeds and acceleration conditions. The attached figure summarizes the analysis of velocities and travel times based on the AASHTO Green Book. Figure 2-24 of the Green Book provides velocity and distance curves for initial velocities ranging from 0 mph to 75 mph. These curves were used to calculate time durations to the conflict point for three conflicting movements and the left-turn egress movement. The attached figure shows the lines of sight from the left-turning egress vehicle to the east. A single vehicle stopped at the stop-bar on Villard Street would create a MARVIN & ASSOCIATES 1300 N. Transtech Way Billings, MT 59102 Mailing Address: P.O. Box 80785 Billings, MT 59108-0785 Phone: 406-655-4550 FAX: 406-655-4991 Page 3 sight restrictive shadow that would partially hide an eastbound thru-vehicle on the eastbound approach. Sight restrictions in the northwest corner would hide a southbound right turning vehicle. It would not be possible to see a northbound left- turning vehicle when it is approaching south of the crosswalk on Willson Avenue. Of the three conflicting vehicles approaching the conflict point from the east, the northbound left-turning vehicle on Willson Avenue would take the shortest amount of time to arrive at the conflict point (6.5 seconds). The amount of time it would take the egress vehicle to arrive at the conflict point would be 4.1 seconds. Thus, at 6.5 seconds the access car would be approximately 55 feet west of the conflict point, with a calculated velocity of 19 mph. At the same time, the conflicting vehicle would just arrive at that same conflict point. This indicates that intersection control would affect operations in a manner that would allow for relatively safe egress movements. e. Location and Alignment. Conflicts with traffic at the alley on the north side of Villard was discussed in item b. The driveway on the north side of Villard Street is on the same relative north-south alignment as the proposed garage access. The driveway accesses a single-car garage located approximately 10’ behind the sidewalk. Since there is no line of sight obstruction involved and conflicting vehicle speeds are at or near zero, any potential conflicts would be apparent to the drivers and could be resolved by careful and prudent driver behavior. If additional information concerning the proposed parking garage access is required, feel free to contact me. Robert R. Marvin, P.E., P.T.O.E. BLOCK 4 GARAGE ACCESS ATTACHMENTS HCS7 Two-Way Stop-Control Report General Information Site Information Analyst R Marvin Intersection Villard & Garage Acc Agency/Co.Marvin & Associates Jurisdiction City of Bozeman Date Performed 9/17/2021 East/West Street Villard Street Analysis Year 2021 North/South Street Garage Access Time Analyzed PM Hour Traffic Peak Hour Factor 0.90 Intersection Orientation East-West Analysis Time Period (hrs)0.25 Project Description NOrth Central Block 4 Lot 1A Lanes Major Street: East-West Vehicle Volumes and Adjustments Approach Eastbound Westbound Northbound Southbound Movement U L T R U L T R U L T R U L T R Priority 1U 1 2 3 4U 4 5 6 7 8 9 10 11 12 Number of Lanes 0 0 1 0 0 0 1 0 0 1 0 0 0 0 Configuration TR LT LR Volume (veh/h)25 6 36 16 7 10 Percent Heavy Vehicles (%)0 0 0 Proportion Time Blocked Percent Grade (%)0 Right Turn Channelized Median Type | Storage Undivided Critical and Follow-up Headways Base Critical Headway (sec)4.1 7.1 6.2 Critical Headway (sec)4.10 6.40 6.20 Base Follow-Up Headway (sec)2.2 3.5 3.3 Follow-Up Headway (sec)2.20 3.50 3.30 Delay, Queue Length, and Level of Service Flow Rate, v (veh/h)40 19 Capacity, c (veh/h)1590 941 v/c Ratio 0.03 0.02 95% Queue Length, Q₉₅ (veh)0.1 0.1 Control Delay (s/veh)7.3 8.9 Level of Service (LOS)A A Approach Delay (s/veh)5.1 8.9 Approach LOS A Copyright © 2021 University of Florida. All Rights Reserved. HCS™TWSC Version 7.9 Generated: 9/17/2021 3:36:44 PMVillard & Garage Access Future.xtw HCS7 Two-Way Stop-Control Report General Information Site Information Analyst R Marvin Intersection Villard & Willson Agency/Co.Marvin & Associates Jurisdiction City of Bozeman Date Performed 9/17/2021 East/West Street Villard Street Analysis Year 2021 North/South Street Willson Avenue Time Analyzed Peak Hour Factor 0.90 Intersection Orientation North-South Analysis Time Period (hrs)0.25 Project Description North Central Block 4 Lot 1A Lanes Major Street: North-South Vehicle Volumes and Adjustments Approach Eastbound Westbound Northbound Southbound Movement U L T R U L T R U L T R U L T R Priority 10 11 12 7 8 9 1U 1 2 3 4U 4 5 6 Number of Lanes 0 1 0 0 1 0 0 0 1 0 0 0 1 0 Configuration LTR LTR LTR LTR Volume (veh/h)10 15 10 5 12 10 25 155 25 15 130 15 Percent Heavy Vehicles (%)0 0 0 0 0 0 0 0 Proportion Time Blocked Percent Grade (%)0 0 Right Turn Channelized Median Type | Storage Undivided Critical and Follow-up Headways Base Critical Headway (sec)7.1 6.5 6.2 7.1 6.5 6.2 4.1 4.1 Critical Headway (sec)7.10 6.50 6.20 7.10 6.50 6.20 4.10 4.10 Base Follow-Up Headway (sec)3.5 4.0 3.3 3.5 4.0 3.3 2.2 2.2 Follow-Up Headway (sec)3.50 4.00 3.30 3.50 4.00 3.30 2.20 2.20 Delay, Queue Length, and Level of Service Flow Rate, v (veh/h)39 30 28 17 Capacity, c (veh/h)540 566 1392 1369 v/c Ratio 0.07 0.05 0.02 0.01 95% Queue Length, Q₉₅ (veh)0.2 0.2 0.1 0.0 Control Delay (s/veh)12.2 11.7 7.6 7.7 Level of Service (LOS)B B A A Approach Delay (s/veh)12.2 11.7 1.1 0.8 Approach LOS B B Copyright © 2021 University of Florida. All Rights Reserved. HCS™TWSC Version 7.9 Generated: 9/17/2021 3:42:09 PMVillard & Willson PM Future.xtw