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HomeMy WebLinkAbout9.0 108 West Babcock Departure Request - Vision Triangle BRIDGER ENGINEERS_INC. 2150 Analysis Dr.,Ste.B Bozeman,MT 59718 (406)585-0590 August 26, 2024 Bozeman City Planning& Engineering 20 E. Olive Street Bozeman, MT 59715 Re: 108 West Babcock Street—Site Plan Application (PLNAPP-8249) Departure Request from Street Vision Triangle Standard Dear Planning& Engineering Staff: This letter is being submitted as a supplement to the 108 W. Babcock Site Plan Application. Specifically, this letter serves as a departure request from the Bozeman UDC provision Section 38.400.100.B which states that"no fence, wall or planting in excess of 30 inches above the street centerline grade is permitted within a triangular area defined as follows...". The departure being requested is to allow a corner of the proposed building to be located in the vision triangle. The proposed project is located on the southwest corner of West Babcock Street and South Wilson Avenue. The intersection is a traffic signal-controlled intersection and West Babcock is a one-way to the east. Given these traffic controls, two vision triangles have been considered for the project. Alley Sight Vision Triangle: The alley off W. Babcock at the west boundary of the property provides access to and from the property. Since both lanes of W. Babcock are restricted to one-way east-bound traffic, the vision triangle extends to the west only. This half of the vision triangle is shown according to the Bozeman UDC provision Section 38.400.100.C. An existing yellow painted curb restricts parking within approximately 10 feet of the alley approach. This existing extent of no-parking shall be maintained with the proposed project and the new alley approach to be constructed. Intersection Sight Vision Triangle: Since the intersection of Babcock& Wilson is a signal-controlled intersection, the AASHTO Green Book method was used to determine the sight vision triangle based on a 25-mph posted speed limit. A Policy on Geometric Design of Highways and Streets, 2018 7th Edition (2nd Printing)published by AASHTO notes the following for intersections with traffic signal control (Section 9.5.3.4): `At signalized intersections, the first vehicle stopped on one approach should be visible to the driver of the first vehicle stopped on each of the other approaches. Left-turning vehicles should have sufficient sight distance to select gaps in oncoming traffic and complete left turns.Apart from these sight conditions, there are generally no other approach or departure sight triangles needed for signalized intersections. Signalization may be an appropriate crash countermeasure for higher volume intersections with restricted sight distance that have experienced a pattern of sight-distance related crashes. BRIDGER ENGINEERS, INC. Page 2 However, if right turns on a red signal are to be permitted from any approach, then the appropriate departure sight triangle to the left should be provided to accommodate right turns from that approach" Due to the one-way east-bound traffic on Babcock Street, the applicable triangle over this property is for the right turn on red at the northbound lane on Wilson. The triangle extends a distance of 240' west from the decision point in the right turn lane as illustrated on the site plan. Departure Request: A departure from Bozeman UDC Section 38.400.100.B for a portion of building within the vision triangle is requested as allowed per Section 38.400.100.E for intersections with traffic signals and one-way streets. As shown on the site plan, the northeast corner of the building(a 6.1 ft x 35.6 ft triangle) is within the vision triangle. Departure Criteria: According to Section 38.400.100.E, the departure criteria are that a revision can be accomplished without jeopardizing the follow three conditions: a) the public's health, safety and welfare: A Policy on Geometric Design of Highways and Streets, 2018 7`h Edition (2"d Printing) published by AASHTO was referenced in developing the intersection vision triangle. Section 9.5.1. notes that"Less sight distance may be needed at roundabouts, signalized intersections, or all-way stop controlled intersections. The sight distance needed under various assumptions of physical conditions and driver behavior is directly related to the type of traffic control, to the maneuvers allowed, to the vehicle speeds, and to the resultant distance traversed during perception-reaction time and braking." An additional reference, the Urban Street Design Guide published by the National Association of City Transportation Officials (NACTO) from 2013,notes "Wide corners with large sight triangles may create visibility,but in turn may cause cars to speed through the intersection, losing the peripheral vision they might have retained at a slower and more cautious speed." The subject intersection consists of minimal grades, a signalized intersection, one-way traffic controls on Babcock, a 25-mph low speed limit, unobstructed views of all first vehicles stopped of each other, and short distances traversed during perception-reaction time and braking. Given the references and intersection parameters noted above, the departure being requested does not compromise the public's health, safety and welfare. b) the intent of this chapter: The intent of the vision triangle is to provide adequate visibility for traffic safety based on the designed operating speeds of the intersecting roadways. The proposed building BRIDGER ENGINEERS, INC. Page 3 encroachment withing the vision triangle still allows for adequate visibility for traffic safety and does not impede the view of all first stopped vehicles. c) the intent of the city's growth policy: The intent of the City's growth policy for this area is to provide high-intensity development with flexibility within the traditional core of downtown Bozeman. Buildings are located within vision triangles all along Main Street, Babcock and Mendenhall in the downtown area. The placement and design of the proposed building not only fits within the existing character of downtown Bozeman but also fits the long-term high-intensity development goals of the community for this area. I hope that you will find the above discussion sufficient justification for approving this departure request. We believe that the proposed request is reasonable given the limited size of the existing lot and the City's future development goals. Thank you for your time and consideration of this request. Sincerely, Melanie Dyba, P.E. Bridger Engineers, Inc.