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Figure 10.3: Critical Sight Distance Clearance Areas
Sight Distance Recommendations
Drivers approaching or departing an intersection should have an unobstructed view of traffic control devices and sufficient length along the crossing road to safely navigate the intersection. According to the Texas Transportation institute “Appropriate intersection sight distance (ISD) reduces the potential for conflicts at intersections. Sight distance is also provided at intersections to allow the drivers of stopped vehicles a sufficient view of the intersecting road.” Sight distances can be limited by terrain, walls, railings, or landscaping. The MMP recommends appropriate considerations to allow for intersection sight distance exceeding the requirements set forth by AASHTO and TXDOT. TXDOT recommends the following factors should be taken into consideration when designing an intersection:
• Adequate sight distance should be provided along both highway approaches and across corners. • Gradients of intersecting highways should be as flat as practical on sections that are to be used for storage of stopped vehicles. • Combination of vertical and horizontal curvature should allow adequate sight distance of the intersection. • Traffic lanes and marked pedestrian walks should be clearly visible at all times. • Lane markings and signs should be clearly visible and understandable from a desired distance. • Intersections should eliminate, relocate, or modify conflict points to the extent allowable in order to improve safety. • Intersections should be evaluated for the effects of barriers, rails, and retaining walls on sight distance. For selecting intersection sight distance, refer to AASHTO’s A Policy on Geometric Design for Highways and Streets. Sight distance criteria are provided for the following types of intersection controls:
• Intersections with no control • Intersections with stop control on the minor road • Intersections with yield control on the minor road • Intersections with traffic signal control • Intersections with all-way stop control • Left turns from the major road
Figure 10.3: Critical Sight Distance Clearance Areas
Source: TTI Urban Intersection Design Guide: Volume 1 – Guidelines
