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.
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.
Characteristics that influence intersection design for residential thoroughfares:
Residential thoroughfares have high volumes of pedestrian activity. Providing the appropriate pedestrian facilities is vitally important for these thoroughfares. Roadway and intersection design should reflect this need for a safe, attractive, and comfortable pedestrian environment.
AASHTO's Guide for the Planning, Design, and Operation of Pedestrian Facilities offers the following as characteristics of good intersection design:
Limited Exposure - Reducing crossing distance, providing refuge islands, and reducing conflict points can minimize a pedestrian's exposure to traffic while crossing an intersection.
Intersections should be as compact as possible in order to minimize crossing distances for pedestrians. For larger intersections, mid-street refuge islands allow pedestrians to cross one lane or direction of traffic at a time. Right-turn-on-red restrictions can also be used to reduce pedestrian exposure in the crosswalk.
On streets with curbside parking, curb extensions can reduce the required crossing distance and time. Curb extensions, as shown in the image at right, can also make pedestrians more visible to drivers.
Consider pedestrian presence when selecting the type of control at intersections. Traffic signals, signs, and markings are used to guide and regulate the multi-modal interaction and movements at intersections. Chapter 2 of the MUTCD discusses the merits of several control measures and describes the warrants for each. For example, stop signs are typically used on minor roads intersecting the arterial street in residential areas, as shown at right. Although stop signs can also be used on major arterials, intersections must be carefully designed to ensure that pedestrians waiting to cross are clearly visible and motorists yield the right-of-way when pedestrians are present.
Generally speaking, traffic signals are less common along residential thoroughfares than the others considered as part of this guide. Even so, the MUTCD signal warrants can be used to assess the appropriateness of a traffic signal along residential thoroughfares where they intersect with other higher-volume streets. Effective warrant evaluation necessitates the use of current, comprehensive data for vehicular and pedestrian traffic and direct field observation by the individuals ultimately making the traffic control recommendations.
Meeting some or all of the eight warrants outlined in the manual does not mandate the use of a traffic signal, but this information should be used by local leaders, planners, and designers in decision-making. Warrant 4, in particular, focuses on pedestrian demand and should be given special attention in mixed use environments.
If traffic signals or mid-block pedestrian crossings are present, they should include Accessible Pedestrian Signals (APSs). APSs provide various types of information to pedestrians with vision impairments. APSs can help create great streets that are accessible for all users. Chapter 4E of the MUTCD provides additional information on APSs and their application.
AASHTO's Guide for the Planning, Design, and Operation of Pedestrian Facilities, describes several types of APSs, including:
Due to the primacy of pedestrians in residential areas, lower vehicular speeds are desirable along the thoroughfare. Lower speeds create less noise and improve the quality of life for residents living along the street. They also make it more convenient and safe for pedestrians along the street.
There are a variety of other intersection design treatments that can help contribute to lower speed environments:
Neighborhood traffic circles (not to be confused with modern roundabouts) are physical circles built in the middle of intersections to slow vehicular speeds down through the intersection.
They prevent through-traffic on the arterial street from driving straight through the intersection by forcing drivers to alter their path of travel around the circle.
If considering neighborhood traffic circles as an intersection design treatment, the following points should be kept in mind:
Modern roundabouts can also be an effective traffic calming method for residential streets. Figure 1 below is a generic depiction of typical modern roundabout features:
Modern roundabouts are very different from neighborhood traffic circles. While they both have "circles in the middle of the intersection, they differ substantially on the size of that central island and in the curvature of the intersection approaches and intersection corners. These features are designed to promote the desired speed through the roundabout, in this case lower speeds. Table 1 provides typical values for a variety of roundabout types. Type selection should be made based on the characteristics of the respective residential street. For the residential place types considered in this guide, the rural categories are not applicable.
More detail on roundabouts is provided in FHWA's Roundabouts: An Informational Guide.
Curb extensions are another intersection treatment that can have a traffic calming effect in residential neighborhoods. Curb extensions narrow the width of the road at the intersection, causing drivers to slow down as they approach. They also decrease the length of crossing distance required for pedestrians.
The design of corner curvature, or curb return radii, at intersections has a direct effect on travel speed. Smaller radii create a sharper turn and force drivers to slow down as they navigate the turn. Larger radii have the opposite effect, allowing drivers to navigate the turn at higher speeds. Smaller radii, therefore, are more desirable for residential streets in an effort to keep travel speeds low.
Bicycle travel should be encouraged and prioritized in residential place types. This mode is an efficient, environmentally responsible choice that provides residents a very economical way to make short trips, presuming that good bicycle accommodations are available.
Treatment of bicycle lanes at intersections can be a delicate balancing act due to the variety of conflicts that bicyclists will encounter, as shown at right. In residential areas, bicycle travel should be prioritized at these locations to ensure user safety and to maximize the attractiveness of the bicycle mode choice.
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