Intersections

Article

Source: FHWA An intersection is defined as the area where two or more roadways join or cross, but also includes elements of the functional area, such as intersection approaches, medians, sidewalks, bike lanes, and other roadside features.

The image at right highlights the physical and functional areas of an intersection. Intersections on great streets must serve all modes of travel.

Automobiles, transit vehicles, pedestrians, and bicyclists should all be given adequate time, space, and directional cues to safely proceed through intersections and continue traveling along the arterial. Balancing the needs of all users at multimodal intersections, while maximizing substantive safety is a complex and important challenge.

Source: FHWA

• Intersections are points of conflict where modes of travel converge, as illustrated in the image at right.
• Intersections should be carefully designed to include and prioritize the most appropriate place-specific design elements.
• Intersecting roadways should cross at an angle of at least 75 degrees, ideally 90 degrees. When the angle of intersection is less than 60 degrees special design treatments may be needed to ensure a reasonable level of safety.
• At intersections, medians can be used to provide separation between opposing traffic, channelization for turn lanes, and refuge for pedestrians.
• Medians with landscaping and tree plantings can also be used to improve intersection (or roadway) aesthetics, although care should be taken not to affect driver or pedestrian visibility and sight distance.

Credit: FHWA

Movement through intersections is controlled using yield signs, stop signs, roundabouts, and traffic signals. The appropriate type of control for a given intersection depends on the place type and the amount of pedestrian and vehicular traffic.

The MUTCD provides guidance for selecting the appropriate type of control for various intersection conditions (see the following links for general information and specifics about signal warrants). 

Different traffic control devices impose varying degrees of delay on pedestrians and vehicles passing through the intersection. The overall efficiency and capacity of a roadway is limited by the delay experienced at its intersections.

Some agencies and municipalities continue widening intersections by adding exclusive, dual, or even triple turn lanes in an effort to minimize delay along the arterial. While these improvements do increase an intersection's vehicular capacity, they also render the intersection more difficult for other modes of travel (especially pedestrians) to navigate. Because turn lane additions are typically retrofit projects they can significantly impact surrounding residences, businesses, and land parcels.

Designing intersections for great streets requires balancing competing needs, interests, and values, and responding to the unique circumstances of each street. Planners, designers, policy makers, and local stakeholders should collaborate to develop a community vision which can be used to guide the design and construction of intersections and roadway improvements.

Resources

PDFs:

• Access to Independence
• Pedestrian Push Button Evaluation Study (FHWA)
• Intersection Design (Mass Highway)
• ITE Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities (See Chapter 10)
• Street Design Manual (San Diego)
• Urban Street Design Guidelines - Intersections (Charlotte)

Links:

• FHWA Flexibility in Highway Design, Chapter 4 - Design Controls
• Massachusetts Design Guide, Chapter 6 - Intersections
• FHWA Roundabouts: An Informational Guide
• Roundabouts 101 - The Modern Roundabout
• East-West Gateway Accessibility Page
• Traffic Congestion Costs - VTPI