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Home My WebLink AboutRIDGEWOOD HILLS 4TH FILING, TRACTS N & T - PDP - 55-84N - SUBMITTAL DOCUMENTS - ROUND 1 - VARIANCE REQUEST-3NO PN/7/d J *n 'd HVOONVN31-IS \) 1 I ---------\ is 0 0 LCUASS for a design speed of 40 mph, tg would need to equal 11.2, or the equivalent of a combination truck. For V,j., equal to 25 mph, ISD equals 275 (rounded to 280 feet as reported in AASHTO Exhibit 9-55). As the majority of the traffic will be passenger vehicles, we propose to use AASHTO's guidelines for sight distance. Unlike AASHTO guidelines, the LCUASS decision point distance (measured from the flowline to the decision point) of 10 feet for local/local intersections and 13 feet for other intersections assumes that the vehicles coming to a stop will not utilize the additional distance provided by the parking and bike lanes on the major road. These values are 7.5 feet for local/local intersections and 2.5 feet for local/minor collector intersections utilizing AASHTO guidelines. Therefore, we also propose to use AASHTO guidelines to determine decision point location. The attached exhibit illustrates the proposed sight distance (based on AASHTO with b equal to 390 feet or 445 feet). The exhibit also illustrates the sight distance as required by LCUASS. With the proposed layout, the AASHTO sight distance triangles will not adversely impact the proposed layout except for requiring additional setback for Lote 11, 12, and At this intersection, the AASHTO sight distance is adequate, whereas the LCUASS would make these lots not buildable. Loonan and Associates, Inc. is looking forward to you granting this variance request to utilize AASHTO guidelines instead of LCUASS guidelines in determining sight distance and decision point location. If you have any questions or comments, please call me at 493-2808. Sincerely, \\\0%\W 111J1iJ/j Z Lga o„�aYid�ts�gci;es, Inc �GHARp Tames°"Lo 4, r ,., °°° a Description Local Road/Local Road Local Road/Minor Collector Intersection Intersection b = the traveled distance and is b = 280 feet b = 445 feet (based on design speed of 40 measured from the center of the mph), b = 390 feet (based on design speed of travel lane of the oncoming vehicle 35 mph) to the center of the travel lane of the stopped vehicle. d = the distance between the d = 7.5 feet (14.5 feet — 7 feet d = 2.5 feet (14.5 feet — 12 feet for the flowline of the major road to `X" for the parking lane). parking and bike lanes). c = the distance from the centerline c = 5 feet (1/2 of a 10 foot c = is 5 feet (1/2 of a 10 foot lane). of the minor road to "X" lane). e = the distance from the centerline e = 5 feet (1/2 of a 10 foot e = 6 feet (1/2 of a 12 foot lane). of the major road to the center of lane). its travel lane Comparison to Standards Referencing Figure 7-16 of the LCUASS, the required sight distance lengths are shown in the table below. It is noted on Figure 7-16 that the sight distance shall be measured to the centerline of the street at local -local street intersections. As no distance was given for other intersection types, distances were taken to the centerline of all streets as well. Description Local Road/Local Road Intersection Local Road/Minor Collector Intersection b = the traveled distance and is measured from b = 260 feet b = 660 feet (based on design the center of the travel lane of the oncoming speed of 40 mph), b = 520 feet vehicle to the center of the travel lane of the (based on design speed of 35 stopped vehicle. h d = the distance between the flowline of the d = 10 feet d = 13 feet major road to "X" In summary, LCUASS sight distance is 215 feet longer (660-445) than AASHTO's sight distance for passenger vehicles based on a design speed of 40 mph. LCUASS sight distance is 130 feet longer (520-390) than AASHTO's sight distance for passenger vehicles based on a design speed of 35 mph. LCUASS sight distance is 20 feet shorter (280-260) than AASHTO's sight distance for passenger vehicles based on a design speed of 25 mph. The location of the decision point is further back on the minor road using LCUASS, and the location of the oncoming vehicle relative to the centerline of the major road is different between LCUASS and AASHTO. Justification According to LCUASS, the following table is a summary of design/posted speed limits: Classification Design Speed (mph) Posted Speed(mph) Local Residential 25 25 Connector Local 30 25 Minor Collector 40 35 Based on AASHTO the ISD (intersection sight distance) equals 1.47V,,,ajortg, (page 663-664 of AASHTO) where tg is the time gap for the minor road vehicle to enter the major road and Vmajor is the design speed of the major road in mph. For passenger cars, tg equals 7.5 second for vehicles at a stop turning left. For Vt„ajor equal to 40 mph, ISD equals 441 (rounded to 445 feet as reported in AASHTO Exhibit 9-55). In order for ISD to equal 660 feet, as reported in P, 0, box 270952 V6,d eo &w, eO 80527 (970) 493-2808 54Z (970) 495- 9735 February 28, 2005 Ms. Katie Moore, Civil Engineer I City of Fort Collins Engineering Department 281 North College Avenue Fort Collins, CO 80521 RE: Variance Request for Ridgewood Hills P.U.D., Fourth Filing Project No. 159 Dear Katie: On behalf of our client, Progressive Living Structures, Loonan & Associates, Inc. is requesting a variance with regards to the required sight distance and decision point locations as summarized in the Larimer County Urban Area Street Standards (referred to as LCUASS within this letter). All streets within this site are residential local streets except for Triangle Drive and Avondale Avenue which are minor collectors. This letter is a request for variance to utilize AASHTO guidelines instead of LCUASS guidelines in determining sight distance and decision point location for the intersection of Triangle Drive and Woodrow Drive — ONLY. As you recall, Triangle Drive was originally designed as a Connector Local Road with a design speed of 30 mph. Issue Chapter 7 of the Larimer County Urban Area Street Standards adopted January 2, 2001 requires the sight distance to be 660 feet for traffic turning onto a minor collector and for the decision point to be 13 feet from the flowline. As described below, the sight distance is based on combination trucks whereas the majority of the traffic generated from this project will be passenger vehicles. The LCUASS decision point distance assumes that the vehicles coming to a stop will not utilize the additional distance provided by the parking and bike lanes. Therefore, we propose to use AASHTO guidelines to determine sight distance and decision point location. Proposed Alternate Design The table below describes the sight distance for vehicles turning left from a stop. The vehicle is assumed to be stopped on the minor road and is turning onto a major road. Referring to the attached diagram and page 660 of AASHTO, the distance between the edge of the travel lane to the decision point "X" is 14.5 feet. It should be noted that the sight distance for vehicles turning left is greater by 1 second (see explanation below under "Justification") than those turning right. Therefore, only sight distances for vehicles turning left are provided.