Visibility and Sight Distance

Intersection design should facilitate eye contact between street users, ensuring that motorists, cyclists, pedestrians, and transit vehicles intuitively read intersections as shared spaces. Visibility can be achieved through a variety of design strategies, including intersection “daylighting,” design for low-speed intersection approaches, and the coordinated placement of traffic control devices, trees, planting, and curbside amenities so as not to impede standard approach, departure, and sight distances.

Overview

Visibility is impacted by the design and operating speed of a roadway. Determining sightlines based on existing or 85th-percentile speeds is not always sufficient. Designers need to proactively lower speeds near conflict points to ensure that sightlines are adequate and movements predictable, rather than widening the intersection or removing sightline obstacles. See: Design Speed.

Sight triangles required for stopping and approach distances are typically based upon ensuring safety at intersections with no controls at any approach. This situation occurs rarely in urban environments, and only at very low-speed, low-volume junctions. At uncontrolled locations where volume or speed present safety concerns, add traffic controls or traffic calming devices on the intersection approach.

In urban areas, corners frequently serve as a gathering place for people and businesses, as well as being the locations of bus stops, cycle parking, and other elements. Design should facilitate eye contact between these users, rather than focus on the creation of clear sightlines for moving traffic.

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.

Fixed objects, such as trees, buildings, signs, and street furniture, in the roadway or on the sidewalk may be deemed to obstruct sightlines for vehicles. These objects should not be removed without prior consideration of alternate safety mitigation measures, such as reduction in traffic speeds, curb extension or geometric design, or the use of additional warning signage.

Design Guidance

Daylight intersections by removing parking within 6–8 m of the intersection.

Site street trees at a minimum of 3 m from the intersection, aligning the street tree on the near side of the intersection with the adjacent building corner. Street trees should be sited 0.8 m from the curb return and 2.5 m from the nearest stop sign.

Lighting is crucial to the visibility of pedestrians, cyclists, and approaching vehicles. Major intersections and pedestrian safety islands should be adequately lit with pedestrian-scaled lights to ensure visibility. In-pavement flashing lights can enhance crossing visibility at night, but should be reinforced by well maintained retroreflective markings. See: Lighting Design Guidance.

In determining the sight distance triangle for a given intersection, use the target speed, rather than the design speed, for that intersection.
Traffic control devices must be unobstructed in the intersection and shall be free of tree cover or visual clutter.

Additional signage may be provided to enhance visibility at intersections, but should not replace geometric design strategies.