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.
Intersections along Neighborhood Shop Thoroughfares
The following is a list of characteristics influencing intersection design for neighborhood shop streets:
The primary challenge in designing intersections in neighborhood areas is meeting the needs of pedestrians while maintaining an adequate level of efficiency for motor vehicle traffic. Pedestrian traffic is a primary mode in neighborhood shop areas. Thoroughfare 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:
Sufficient Crossing Time - Signals should be programmed to ensure that all users, including the elderly and individuals with disabilities, have adequate time to safely cross the intersection. Newer pedestrian signals, such as the one shown in the image at right, provide countdown clocks which clearly communicate to pedestrians the time remaining to complete the crossing.
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 thoroughfares with curbside parking, curb extensions can reduce the required crossing distance. 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 major roadway in neighborhood shop environments. Although stop signs can also be used on major roadways, 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.
The MUTCD signal warrants can be used to assess the appropriateness of a traffic signal along a neighborhood shop street.
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 neighborhood shop environments.
Roundabouts are not appropriate in neighborhood shop areas, where there are high volumes of pedestrian crossings. Roundabouts create a constant flow of vehicular traffic and impede pedestrian movement across the thoroughfare.
Restrict turning movements during peak traffic. If traffic signals will be used at a particular intersection along the thoroughfare, several signal timing regulations can be implemented to improve vehicular and pedestrian operations. For example, limiting or prohibiting left turns, either throughout the day or at peak periods, can free up more "green time" for through traffic and improve vehicle operations. Prohibiting right turn on red helps maintain the primacy of service for pedestrians during walk intervals that correspond with red-light phases.
Provide improved pedestrian facilities. Intersections are points of conflict and pedestrians are the most vulnerable users. Directional signage and pedestrian indicators should be used to safely and efficiently guide pedestrians through signalized intersections in neighborhood shop corridors. Countdown clocks are a specific type of indicator using an active countdown display to communicate to pedestrians the time remaining to complete the crossing maneuver.
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:
Keep curb radii small. Transit vehicles and users are typically more prevalent along neighborhood shop corridors, and their presence should significantly influence the design of intersections, particularly curb return radii. Consistent with ITE's Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities, this guide recommends that curb return radii be as small as practicable in urban settings.
Consider channelized right turns when necessary and appropriate. In neighborhood shop environments, the turning radii of buses should be used to select curb return radii only for intersections along designated bus routes. In these locations, additional design elements, such as channelized right turns, should be considered to enhance and protect pedestrian activity.
Chapter 10 of the ITE publication Context Sensitive Solutions in Designing Major Urban Thoroughfares for Walkable Communities provides additional information and guidance about channelized right turn lanes. While this treatment is not typically favored in areas with a significant pedestrian presence, well-designed channelized right turns can improve crossing conditions if and when large vehicles need to be accommodated. A well-designed channelized right turn should:
When these channelized turning radii requirements are not feasible, an alternative is to keep curb return radii small but offset sidewalks, light poles, street furniture, and other streetside amenities, allowing the occasional large vehicle to ride over the curb to negotiate the turn without conflicts.
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