- When a vehicle crosses a major road from a left-skewed minor road, the motorist’s line of sight is obstructed by portions of their vehicle (e.g., roof posts, door frames). AASHTO recommends that intersection skew not exceed 60 degrees. Table 10.4 lists available sight distances (ASDs) and design speeds for 14.4 ft and 17.7 ft setbacks. Use the desirable vision angle if possible — it benefits larger vehicles and older drivers.
| Table 10.4 Available Sight Distances and Design Speeds for 14.4 ft and 17.7 ft Setbacks | ||||||||
| Intersection Angle (Degrees) | Resulting ASD for a 17.7 ft Setback | Resulting ASD for a 14.4 ft Setback | ||||||
| Minimum Vision Angle: 13.5° | Desirable Vision Angle: 4.5° | Minimum Vision Angle: 13.5° | Desirable Vision Angle: 4.5° | |||||
| ASD (ft) | Design Speed (mph) | ASD (ft) | Design Speed (mph) | ASD (ft) | Design Speed (mph) | ASD (ft) | Design Speed (mph) | |
| 55 | 104.3 | 19 | 77.4 | < 19 | __ | __ | __ | __ |
| 60 | 130.6 | 23 | 88.3 | < 19 | 119.4 | 22 | 80.7 | < 19 |
| 65 | 181.8 | 29 | 106.0 | 20 | 165.7 | 28 | 96.8 | 19 |
| 70 | 314.0 | 40 | 136.5 | 24 | 285.8 | 38 | 124.0 | 22 |
| 75 | 1,339.2 | > 75 | 197.2 | 30 | 1,217.5 | > 75 | 179.1 | 29 |
CONTACT:
Chris VanDyke
Research Scientist | Program Manager
chrisvandyke@uky.edu
