The required vision clearance triangle shall be a sight distance as specified in Table 12.11.020, Vision Clearance Triangle – Minimum Dimensions. The standard dimensions from the table shall be used unless a striped bike lane or legal on-street parking is present, in which case the alternate dimensions may be used. At signalized intersections, Dimensions B and C shall be as provided in Table 12.11.020, using the rows for right-turns only. The minimum standard in Table 12.11.020 may be increased or decreased by the public works director upon recommendation by the traffic engineer for locations where horizontal curvature along the main roadway is present such that a site-specific calculation is necessary to establish a safe sight distance. In these cases, the vision clearance triangle will be established based upon the guidelines in the 2011 American Association of State Highway and Transportation Officials (AASHTO) Edition of "A Policy on Geometric Design of Highways and Streets," Chapter 9, with driver setbacks of 14.5 feet as well as driver and object heights of three and one-half feet each.
For marked crosswalks, available sight distance between an approaching vehicle and pedestrians at a crosswalk shall be required to be at least the stopping sight distance (SSD) for approaching vehicles as identified in Table 12.11.020 and measured from the back of sidewalk at the pedestrian ramp(s) to the drivers' eye position on the roadway approach.
Standard vision clearance triangles for roundabouts shall be defined by a line drawn from the back of sidewalk at the pedestrian ramp on the roundabout approach leg to the back of sidewalk at the pedestrian ramp on the immediate downstream departure leg which also encompasses the entire flat landing areas for the pedestrian ramps. Variances to increase or decrease the standard roundabout vision clearance triangle may be required or allowed by the public works director upon recommendation of the traffic engineer. Typically, these recommendations would be based on required stopping sight distance using guidelines established in the 2011 American Association of State Highway and Transportation Officials (AASHTO) Edition of "A Policy on Geometric Design of Highways and Streets," Chapter 3, using a brake reaction time of 1.0 seconds since the driver should be in an alerted state due to entering a controlled intersection.
Table 12.11.020 Vision Clearance Triangle - Minimum Dimensions |
|---|
MPH | Number of Thru Approach Lanes from the Left | Standard Vision Clearance Dimensions Measured from Curb Line or Edge of Pavement | Alternate Vision Clearance Dimensions When Parking or Bike Lane Is Present Measured from Curb Line or Edge of Pavement | Stopping Sight Distance (SSD) |
|---|
A | B | C | A | B | C |
|---|
25 | Right-Turns Only | 13 | 155 | 50 | 8 | 95 | 50 | 155 |
1 | 180 | 110 | 110 | 70 |
2 | 190 | 85 | 120 | 55 |
3 | 205 | 70 | 125 | 45 |
30 | Right-Turns Only | 13 | 185 | 50 | 8 | 115 | 50 | 200 |
1 | 215 | 135 | 135 | 85 |
2 | 230 | 105 | 145 | 65 |
3 | 245 | 85 | 155 | 55 |
35 | Right-Turns Only | 13 | 220 | 50 | 8 | 135 | 50 | 250 |
1 | 255 | 155 | 160 | 100 |
2 | 270 | 120 | 170 | 75 |
3 | 290 | 100 | 180 | 65 |
40 | Right-Turns Only | 13 | 250 | 50 | 8 | 155 | 50 | 305 |
1 | 295 | 180 | 180 | 110 |
2 | 315 | 140 | 195 | 85 |
3 | 335 | 115 | 205 | 75 |
45 | Right-Turns Only | 13 | 285 | 50 | 8 | 175 | 50 | 360 |
1 | 330 | 205 | 205 | 125 |
2 | 355 | 155 | 220 | 100 |
3 | 375 | 130 | 230 | 80 |
(Ord. 10-86 § 1.11; Ord. 41-15 § 1; Ord. 59-17 § 1)