Graphics header for Chapter 10 Intersection Design Guidelines

Introduction

Multimodal intersections operate with pedestrians, bicycles, cars, buses and trucks, and in some cases, trains. The diverse uses of intersections involve a high level of activity and shared space. Intersections have the unique characteristic of accommodating the almost-constant occurrence of conflicts between all modes, and most collisions on thoroughfares take place at intersections. This characteristic is the basis for most intersection design standards, particularly for safety.

Designing multimodal intersections with the appropriate accommodations for all users is performed on a case-by-case basis. The design extends beyond the immediate intersection and encompasses the approaches, medians, streetside and driveways, and adjacent land uses (Figure 10.1). The designer should begin with an understanding of the community objectives and priorities related to design trade-offs such as vehicular capacity and level of service, large-vehicle turning requirements, conflicts, pedestrian and bicycle convenience, accessibility and the efficiency of public transit service. Intersections are perhaps the most sensitive operational component of thoroughfare systems (Figure 10.2).

In urban areas, intersections have a significant place-making function as well as a transportation function. Significant land uses and architecturally significant buildings are located at intersections and might provide pedestrian access directly from the corners. Intersections may also serve as gateways and are frequently the first thing visitors see when they enter a neighborhood (Figure 10.3). It is often requested that the practitioner include aesthetic treatments in intersection design.

Diagram depicting the design of intersections encompasses the intersection itself and the approaches to the intersection. It can even affect adjacent land uses.

Figure 10.1 The design of intersections encompasses the intersection itself and the approaches to the intersection. It can even affect adjacent land uses. Source: Digital Media Productions.

Photo of an intersection showing the unique characterist of accommodating the almost constant occurence of conflicts between all modes. This photo shows an intersection with turn lanes, a bicycle lane, crosswalks, traffic lights, sidewalks, pedestrians, bicyclist and cars.

Figure 10.2 Intersections have the unique characteristic of accommodating the almost-constant occurrence of conflicts between all modes. Source: Texas Transportation Institute.

 

Objectives

This chapter:

1. Describes several fundamental aspects of intersection design, including managing multimodal conflicts, sight distance and layout; and

2. Provides general principles, considerations and design guidelines for key intersection components including curb return radii, channelized right turns, modern roundabouts, crosswalks, curb extensions, bicycle lanes and bus stops.

General Principles and Considerations

Intersections are required to meet a variety of user expectations, particularly for users of motor vehicles. Drivers expect to safely pass through intersections with minimal delay and few conflicts. Drivers of large vehicles expect to be able to negotiate turns easily. In urban areas, however, expectations based on rural and suburban experiences are unreasonable. Intersection users in urban areas will experience delays and conflicts between vehicles, pedestrians and bicyclists. Driver expectations need to shift toward taking turns with other modes and a sense of uncertainty, which creates a slower, vigilant and safer environment.

Successful multimodal intersection design is based on several fundamental geometric design and operational principles. These principles include:

Photo of landscaping in the center island of an intersection.

Figure 10.3 Intersections are community gateways. Landscaping in the center island of an intersection. Source: Kimley-Horn and Associates, Inc.

Photo of an intersection with a crosswalk. The curb extension is equipped with curb ramps and high-contrast detectable warnings.

Figure 10.4 Intersections must be accessible to pedestrians with disabilities. This curb extension is equipped with curb ramps and high-contrast detectable warnings. Source: Kimley-Horn and Associates, Inc.

Considerations regarding intersection design include the following:

Diagram showing an intersection with crosswalks, sidewalks and showing the vehicle path, line of sight and clear sight triangle. Sight distance triangle at intersections. The required sight distance varies with the type of intersection control.

Figure 10.5 Sight distance triangle at intersections. The required sight distance varies with the type of intersection control. Refer to AASHTO Green Book for more details. Source: Kimley-Horn and Associates, Inc.

 

Intersection Sight Distance

Specified areas along intersection approaches, called clear sight triangles (shown in Figure 10.5), should be free of obstructions that block a driver's view of potentially conflicting vehicles or pedestrians entering the traveled way. The determination of sight triangles at intersections varies by the target speed of the thoroughfares, type of traffic control at the intersection and type of vehicle movement.

In urban areas, intersection corners are frequently entrances to buildings and are desirable locations for urban design features, landscaping and other streetside features. In designing walkable urban thoroughfares, the practitioner works in an interdisciplinary environment and has a responsibility to balance the desire for these streetside features with the provision of adequate sight distance, ensuring safety for all users. In urban areas, examples of objects that limit sight distance include vehicles in adjacent lanes, parked vehicles, bridge piers and abutments, large signs, poorly pruned trees, tall shrubs and hedges, walls, fences and buildings.

Considerations regarding intersection sight distance include the following:

Managing Modal Conflict at Intersections

Strategies to eliminate or avoid conflict can result in designs that favor one mode over others. For example, eliminating crosswalks at an urban intersection with a high volume of turning vehicles as a strategy to eliminate conflicts will discourage walking. The practitioner must weigh the ever-present trade-offs between vehicle level of service, large-vehicle accommodation and pedestrian and bicycle connectivity and convenience. For the most part, in urban areas, the tradeoffs are clear; every user shares the intersection and equally shares in the benefits and drawbacks of mul-timodal design.

In locations where the community places a high priority on vehicular level of service, intersection designs should incorporate mitigating measures such as pedestrian countdown signals, pedestrian refuge islands and the replacement of free-flow right turns with low-speed channelized right turns (see applicable section in this chapter).

When improving safety at intersections, it is important that the measures that are used to improve vehicle traffic flow or reduce vehicle crashes not compromise pedestrian and bicycle safety. Safety aspects need to be identified in an engineering review. The following strategic decisions need to be considered when improving intersection safety design and operation:

Traffic engineering strategies can be highly effective in improving intersection safety. These strategies consist of a wide range of devices and operational modifications. Some examples include the following:

Design Elements for Intersections in Walkable Areas

Most urban signalized intersections provide basic pedestrian facilities, including crosswalks, pedestrian signal heads, curb ramps and appropriate pedestrian clearance times. Many urban and especially suburban unsignalized intersections are unmarked for pedestrians. Older intersections in walkable urban areas need to be updated to conform to Americans with Disabilities Act (ADA) Public Rights-of-Way Accessibility Guidelines (PROWAG) requirements, better serve bicyclists, improve transit operations, or to simply enhance the pedestrian environment. This section provides a summary of intersection design features the practitioner may want to consider when designing walkble urban intersections.

Uncontrolled Intersections

Common engineering practice is to exclude marked crosswalks from intersections without traffic control approaching the crossing. This is due to a number of factors including avoiding a false sense of security provided by crosswalks when traffic is uncontrolled, encouraging pedestrian caution when legally crossing at intersections without crosswalks, as well as raising liability and maintenance concerns. Indeed, several research studies have shown that pedestrian-vehicle crash rates are higher at unsignalized intersections with marked crosswalks versus those without.

The authors of NCHRP Report 562, Improving Pedestrian Safety at Unsignalized Intersections, found that the "safest and most effective pedestrian crossings use several traffic control devices or design elements to meet the information and control needs of both motorists and pedestrians." The NCHRP study and other research has found that marked crosswalks alone are insufficient and, when used, should be used in conjunction with other measures depending on the circumstances. In combination with marked crossings, measures to enhance uncontrolled intersections include:

Signalized Intersections

Signalized intersections, while providing some level of pedestrian protection by controlling traffic, have many available design features that increase pedestrian visibility, information and convenience. These features are listed in Table 10.1.

Design Guidance Intersection Geometry

This section provides general principles, considerations and guidelines on the geometric layout of urban at-grade multimodal intersections and the key components that comprise geometric and operational design. These guidelines include a section on the application and design of modern roundabouts as an alternative to the conventional intersection.

Table 10.1 Pedestrian and Bicycle Features at Signalized Intersections

Shorter and more visible crosswalks
  • Crosswalks on all approaches;
  • Longitudinal markings (possible use of colored and/or textured paving);
  • Reduced overall street widths by reducing the number of travel and turn lanes, or narrowing travel lanes;
  • Curb extensions with pedestrian push buttons on extensions; and
  • Median refuges on wide streets (greater than 60 feet) with median push buttons.
Priority for pedestrians, bicyclists, and accessibility
  • Shorter cycle lengths, meeting minimum pedestrian clearances (also improves transit travel times);
  • Longer pedestrian clearance times (based on 3.5 feet/sec. to set flashing (clearance) time and 3.0 feet/sec for total crossing time);
  • Reduced conflicts between pedestrians and turning vehicles achieved with:
  • Pedestrian lead phases;
  • Scramble phases in very high pedestrian volume locations;
  • Restricted right turns on red when pedestrians are present during specified hours; and
  • Allowing right turns during cross-street left turn phases reduces the number of right turn conflicts during pedestrian crossing phase.
Low speed channelized right turn lanes
  • Adequate sized islands for pedestrian refuge;
  • Raised pedestrian crossing/speed table within channelized right turn lane; and
  • Signal control of channelized right turn in high pedestrian volume locations.
Improved pedestrian information
  • Pedestrian countdown timers; and
  • "Look Before Crossing" markings or signs.
Bicycle features
  • Bicycle lanes striped up to crosswalk (using "skip lines" if vehicular right turns are allowed);
  • Bicycle detectors on high volume routes, or bicyclist-accessible push buttons;
  • Adequate clearance interval for bicyclists;
  • Colored paving in bicycle/vehicle lanes in high-conflict areas; and
  • "Bike Boxes" (painted rectangle along right hand curb or behind crosswalk) to indicate potential high-conflict area between bicycles continuing through an intersection and right turning vehicles, and to allow bicyclists to proceed through intersection or turn in advance of vehicles.
High-priority transit
thoroughfare
elements
  • Adaptive Transit Signal Priority (TSP) when transit detected:
  • Extended green phase on bus route (rapid transit signal priority);
  • Truncated green phase for cross street;
  • Re-order phasing to provide transit priority (transit priority not to be given in two successive cycles to avoid severe traffic impacts);
  • Other bus priority signal phasing (sequencing)
  • Queue jump lanes and associated signal phasing; and
  • Curb extension bus stops, bus bulbs.
Accessibility and space for pedestrians
  • Properly placed pedestrian actuation buttons, with audible locator tones;
  • Detectable warnings;
  • Two curb ramps per corner depending on radius of curb return and presence of curb extensions;
  • Clear pedestrian paths (and shoulder clearances) ensuring utilities and appurtenances are located outside pedestrian paths;
  • Vertical and overhang clearance of street furnishings for the visually impaired;
  • Properly placed signal poles and cabinets:
  • Behind sidewalks (in landscaping or in building niches);
  • In planting strips (furnishings zone); and
  • In sidewalk or curb extensions, at least three feet from curb ramps.
Traffic operations for safe speeds and pedestrian convenience
  • Target speeds between 25-35 mph;
  • Signal progression at target speeds; and
  • Fewer very long/very short cycle lengths.
Higher priority on aesthetics
  • Textured and colored material within the streetside;
  • Colored material within crosswalks, but avoid coarse textures which provide rough surfaces for the disabled;
  • Attractive decorative signal hardware, or specialized hardware; and
  • Attention to landscaping and integration with green street stormwater management techniques.

 

Diagram of an intersection showing multiple lanes, turn lanes, areas with driveways, crosswalks and cars in various positions of travel or parking. It shows the Intersection Functional Area, where there are no driveways. Areas just outside the Intersection Functional Area contain the label Driveway OK.

Figure 10.6 Many decisions are made within the functional area of an intersection. Source: Community, Design + Architecture.

General Intersection Layout

Intersection layout is primarily composed of the alignment of the legs; width of traffic lanes, bicycle lanes, crosswalks, and sidewalks on each approach number of lanes, median and streetside elements; and the method of treating and channelization of turning movements. Like the design of the thoroughfare's cross-section, the design of an intersection's layout requires a balance between the needs of pedestrians, bicyclists, vehicles, freight and transit in the available right of way. Beyond intersection layout, the practitioner needs to work with a multidisciplinary team to address accessibility, traffic control and placement of equipment, traffic operations, lighting (safety and pedestrian scaled), landscaping and urban design.

Intersection Fundamentals

Intersections are composed of a physical area—the area encompassing the central area of two intersecting streets as shown in Figure 10.6. The functional area is where drivers make decisions and maneuver into turning movements. The three parts of the functional area include (1) the perception-reaction distance, (2) maneuver distance and (3) storage distance. AASHTO's A Policy on Geometric Design of Highways and Streets (2004a) addresses the issues and provides guidance for the detailed geometric design of the functional area.

The basic types of intersections in urban contexts include the T-intersection (a three-leg intersection), cross-intersection (four-leg intersection), multileg intersection (containing five or more legs) and the modern roundabout, which is discussed later in this chapter.

Intersection Conflicts

Intersections, by their very nature, create conflicts between vehicles, pedestrians and bicyclists. Figure 10.7 illustrates the number of conflicts between different modes at three- and four-leg intersections. According to AASHTO's Guide for the Planning, Design and Operation of Pedestrian Facilities (2004b), the following are principles of good intersection design for pedestrians:

This diagram depicts an intersection demonstrating 32 vehicle/vehicle conflicts and 16 pedestrian/vehicle conflicts.

This diagram depicts an intersection with 9 vehicle/vehicle conflicts and 12 pedestrian/vehicle conflicts.

Figure 10.7 Vehicle and pedestrian conflicts at three- and four-leg intersections. Source: Community, Design + Architecture, adapted from an illustration by Michael Wallwork.

 

General Principles and Considerations

General principles and considerations for the design of intersection layouts include the following:

Curb Return Radii Background and Purpose

Related Thoroughfare Design Elements

Curb returns are the curved connection of curbs in the corners formed by the intersection of two streets. A curb return's purpose is to guide vehicles in turning corners and separate vehicular traffic from pedestrian areas at intersection corners. The radius of the curve varies, with larger radii used to facilitate the turning of large trucks and buses. Larger radius corners increase the length of pedestrian crosswalks, and increase vehicular turning speeds.

In designing walkable urban thoroughfares, the smallest practical curb-return radii are used to shorten the length of the pedestrian crosswalks. Based on this function, this report suggests a general strategy for selecting curb-return radii design criteria and discusses situations requiring larger design vehicles. The primary benefits of smaller curb-return radii to pedestrians in urban areas include:

General Principles and Considerations

General principles and considerations regarding curb return radii include the following:

Diagram depicts intersection showing radius of conventional curb return radius to acommodate large design vehicle. Smaller curb-return radii shorten the distance that pedestrians must cross at intersections. The occasional turn made by large trucks can be accommodated with slower speeds and some encroachment into the opposing traffic lanes.

Figure 10.8 Smaller curb-return radii shorten the distance that pedestrians must cross at intersections. The occasional turn made by large trucks can be accommodated with slower speeds and some encroachment into the opposing traffic lanes. Source: Kimley-Horn and Associates, Inc.

This diagram depics a turning radius that overlaps a bicycle lane. R1 shows the actual curb radius and R2 shows the effective radius.

Figure 10.9 The existence of parking and bicycle lanes creates an "effective" turning radius that is greater than the curb-return radius. Source: Kimley-Horn and Associates, Inc., adapted from the Oregon Bicycle and Pedestrian Plan.

Recommended Practice

Flexibility in the design of curb return radii revolves around the need to minimize pedestrian crossing distance, the choice of design vehicle, the combination of dimensions that make up the effective width of the approach and receiving lanes and the curb return radius itself. The practitioner needs to consider the trade-offs between the traffic safety and operational effects of infrequent large vehicles and the creation of a street crossing that is reasonable for pedestrians. The guidelines assume arterial and collector streets in urban contexts (C-3 to C-6) with turning speeds of city buses and large trucks of 5 to 10 mph. The guidance is not applicable to intersections without curbs.

Recommended practices include the following:

• In urban centers (C-5) and urban cores (C-6) at intersections with no vehicle turns, the minimum curb return radii should be 5 feet.

• A curb return radius of 5 to 15 feet should be used where:

1. High pedestrian volumes are present or reasonably anticipated;

2. Volumes of turning vehicles are low;

3. The width of the receiving intersection approach can accommodate a turning passenger vehicle without encroachment into the opposing lane;

4. Large vehicles constitute a very low proportion of the turning vehicles;

5. Bicycle and parking lanes create additional space to accommodate the "effective" turning radius of vehicles;

6. Low turning speeds are required or desired; and

7. Occasional encroachment of turning school bus, moving van, fire truck, or oversized delivery truck into an opposing lane is acceptable.

• Curb radii may need to be larger where:

1. Occasional encroachment of a turning bus, school bus, moving van, fire truck, or oversized delivery truck into the opposing lane is not acceptable;

2. Curb extensions are proposed or might be added in the future; and

3. Receiving thoroughfare does not have parking or bicycle lanes and the receiving lane is less than 12 feet in width.

An alternative to increasing curb-return radii is setting back the stop line of the receiving street to allow large vehicles to swing into opposing lane as they turn. However, setbacks to accommodate right-turn encroachment need to be examined on a case-by-case basis since very tight right turns may require long setbacks.

Recommendations for Curb Radii on Transit and Freight Routes

Truck routes should be designated outside of or on a minimum number of streets in walkable areas to reduce the impact of large turning radii. Where designated local or regional truck routes conflict with high pedestrian volumes or activities, analyze freight movement needs and consider redesigna-tion of local and regional truck routes to minimize such conflicts.

On bus and truck routes, the following guidelines should be considered:

Justification

Intersections designed for the largest turning vehicle traveling at significant speeds with no encroachment result in long pedestrian crossings and potentially high-conflict areas for pedestrians and bicyclists. Radii designed to accommodate the occasional large vehicle will allow passenger cars to turn at high speeds. In designing walkable urban thoroughfares, the selection of curb returns ranging from 5 to 25 feet in radius is preferable to shorten pedestrian crossings and slow vehicle-turning speeds to increase safety for all users.

Channelized Right-Turns

Background and Purpose

Related Thoroughfare Design Elements

In urban contexts, high-speed channelized right turns are generally inappropriate because they create conflicts with pedestrians and bicyclists and also increase turning speeds. Under some of the circumstances described below, providing channelized right-turn lanes on one or more approaches at a signalized intersection can be beneficial, but unless designed correctly, these right-turn lanes can be undesirable for pedestrians. According to the Oregon Bicycle and Pedestrian Plan a well-designed channelization island can:

Right-turning drivers may not have to stop for the traffic signal when a channelized right-turn lane is provided. Even where pedestrian signal heads are provided at the intersection, pedestrians are usually expected to cross channelized right-turn lanes without the assistance of a traffic signal. Most channelized right-turn lanes consist of only one lane, and the crossing distance tends to be relatively short. However, drivers are usually looking to their left to merge into cross-street traffic and are not always attentive to the presence of pedestrians.

A photo showing an intersection with a pedestrian refuge island and an incontrolled crosswalk. The photo shows people on the pedestrian refuge island as they cross the street.

Figure 10.10 A channelized right-turn lane typically provides a pedestrian refuge island and an uncontrolled crosswalk. Source: Dan Burden, walklive.org.

General Principles and Considerations

The general principles and considerations regarding channelized right turns include the following:

Recommended Practice

Recommended practices regarding channelized right-turn lanes include the following:

 

Please see extended text description below

Figure 10.11 The preferred design of a channelized right-turn lane uses an approach angle that results in a lower speed and improved visibility. Source: Kimley-Horn and Associates, Inc., adapted from an illustration by Dan Burden.

(Extended text description: The diagram depicts two designs of a channelized right-turn lane. The first shows a wide angle design with a high-speed, low visibility of pedestrians with a 20 degree to 142 degreen angle. The second design shows a tighter angle showing a 20 degree to 112 degree angle, with a 55 to 60 degree angle between vehicle flows.)

 

Chapter 10: Intersection Design Guidelines 189

Diagram depicts a typical single-lane modern roundabout design provides yield control on all approaches and deflects approaching traffic to slow speeds.

Figure 10.12 A typical single-lane modern roundabout design provides yield control on all approaches and deflects approaching traffic to slow speeds. Source: Community, Design + Architecture, adapted from an illustration in Roundabouts, An Informational Guide (FHWA).

Modern Roundabouts

Background and Purpose

Related Thoroughfare Design Elements

Modern roundabouts are an alternative form of intersection control that is becoming more widely accepted in the United States. In the appropriate circumstances, significant benefits can be realized by converting stop-controlled and signalized intersections into modern roundabouts. These benefits include improved safety, speed reduction, reduction in certain types of vehicle crashes, opportunities for aesthetics and urban design, and operational functionality and capacity.

Studies conducted in the United States and published by the Federal Highway Administration in Roundabouts: An Informational Guide (2000) indicate that modern single-lane roundabouts in urban areas can result in up to a 61 percent reduction in all crashes and a 77 percent reduction in injury crashes when compared with stop-controlled intersections. When signalized intersections are replaced by modern single-lane roundabouts in urban areas, they have resulted in up to a 32 percent reduction in all crashes and up to a 68 percent reduction in injury crashes.

There remain some concerns regarding roundabouts and pedestrian and bicycle safety and how the disabled are accommodated. Care should be taken in areas with particularly high pedestrian volumes to provide adequate crosswalk widths and island dimensions to serve the volume of pedestrians moving around the roundabout. Double-lane roundabouts are of particular concern to pedestrians with visual impairments and bicyclists.

General Principles and Considerations

The purpose of a modern roundabout is to increase vehicle capacity at the intersection, slow traffic and reduce the severity of collisions. They are not generally used to enhance pedestrian and bicycle safety. Roundabouts are not always the appropriate solution. General principles and considerations for the design of modern roundabouts include the following:

Overhead photo depicting a typical layout of a single lane modern roundabout surrounded by trees and buildings.

Figure 10.13 Typical layout of a single lane modern roundabout. Source: Kimley-Horn and Associates, Inc.

Recommended Practice

Table 10.2 provides guidance for the selection of modern roundabouts for various thoroughfare types and presents general design parameters. There are three general roundabout design philosophies in use in the United States. First, many older traffic circles and rotaries are being eliminated or redesigned to modern roundabouts. Second, the Australian model of smaller-diameter and slower speed roundabouts is gaining popularity in the United States, as is the third, the British model of larger-diameter, multilane, higher-speed roundabouts. The designer should reference the planning section of FHWA's informational guide to aid in the decision-making process.

Justification

Roundabouts exist at more than 15,000 intersections in Europe and Australia, with decades of successful operation, research and improvements. Introduced into the United States in the 1990s, modern roundabouts are much improved over older American traffic circles and rotaries. Significant benefits related to crash and delay reduction are cited by researchers based on conversion of four-way stop-controlled and signal-controlled intersections in eight states.

Table 10.2 Recommended Practice for Modern Roundabouts

Parameter Minimum "Mini-Roundabout" Urban Compact Roundabout Urban Single-Lane Roundabout Urban Double-Lane Roundabout*
Maximum Entry Speed (mph) 15 15 20 25
Design Vehicle Bus and single-unit truck drive over apron Bus and single-unit truck Bus and single-unit truck
WB-50 with lane encroachment on truck apron
WB-67 with lane encroachment on truck apron
Inscribed circle diameter (feet) 45 to 80 80 to 100 100 to 130 150 to 180
Maximum number of entering lanes 1 1 1 2
Typical capacity (vehicles per day entering from all approaches) 10,000 15,000 20,000 40,000
Applicability by Thoroughfare Type:
Boulevard Not Applicable Not Applicable Not Applicable Applicable
Arterial Avenue Not Applicable Not Applicable Applicable Applicable
Collector Avenue Applicable Applicable Applicable Not Applicable
Street Applicable Applicable Applicable Not Applicable

* Note the pedestrian and bicycle conflicts are inherent in multilane roundabouts unless they are signalized.

Pedestrian Treatments at Intersections—Crosswalks

Background and Purpose

Related Thoroughfare Design Elements

Crosswalks are used to assist pedestrians in crossing streets. The definition provided in the MUTCD of an unmarked crosswalk makes it clear that unmarked crosswalks can exist only at intersections, whereas the definition of a marked crosswalk makes it clear that marked crosswalks can exist at intersections "or elsewhere." Crosswalks also provide the visually impaired with cues and wayfinding, as long as they have appropriate contrast.

If sidewalks exist on one or more quadrants of the intersection at a signalized or unsignalized intersection, then crosswalks are legally present at the intersection whether they are marked or not. Even if sidewalks do not exist at the intersection, in some states crosswalks may be legally present.

Even if unmarked crosswalks legally exist at a signalized intersection, it is almost always beneficial to provide marked crosswalks from the perspective of pedestrian safety. Marked crosswalks alert drivers approaching and traveling through the intersection of the potential presence of pedestrians. Marked crosswalks also direct legal pedestrian movements to desirable crossing points.

If an unmarked crosswalk legally exists across a stop-controlled approach to an intersection, it is usually not necessary to mark the crosswalk. However, if engineering judgment determines that pedestrian safety or the minimization of vehicle-pedestrian conflicts is especially important, then providing a marked crosswalk along with advanced warning signs and markings would be appropriate.

General Principles and Considerations

In designing thoroughfares, the issue of crosswalks is not isolated to an individual intersection. The intent of CSS in walkable areas is to create an environment in which pedestrians and bicycles are expected and to support this expectation with consistent and uniform application of signing, markings and other visual cues for motorists and pedestrians. The following principles and considerations should help guide the planning or design of pedestrian crossings:

Diagram showing the three primary types of crosswalk markings (from left to right) are transverse, longitudinal and diagonal.

Figure 10.14 The three primary types of crosswalk markings (from left to right) are transverse, longitudinal and diagonal. Source: Kimley-Horn and Associates, Inc.

Photo showing an interesection with crosswalks with colored bricks. Crosswalks with colored bricks contrast with concrete pavement. However, over time, colored bricks stain and lose contrast. Painted stripes marking brick or colored concrete crosswalks would increase their visibility. Otherwise use standard crosswalk markings for long-term visibility.

Figure 10.15 Crosswalks with colored bricks contrast with concrete pavement. However, over time, colored bricks stain and lose contrast. Painted stripes marking brick or colored concrete crosswalks would increase their visibility. Otherwise use standard crosswalk markings for long-term visibility. Source: Kimley-Horn and Associates, Inc.

 

Care should be taken to ensure that the material used in these crosswalks is smooth, nonslip and visible. Avoid using a paver system that may shift and/or settle or that induces a high degree of vibration in wheelchair wheels.

Recommended Practice

The following practice is recommended:

Justification

Marked crosswalks are one tool to get pedestrians safely across the street and they should be used in combination with other treatments (such as curb extensions, pedestrian refuge islands, proper lighting and so forth). In most cases, marked crosswalks alone (without other treatments) should not be installed within an uncontrolled environment when speeds are greater than 40 mph according to AASHTO's Guide for the Planning, Design and Operation of Pedestrian Facilities (2004b) and FHWA's Safety Effects of Marked vs. Unmarked Crosswalks at Uncontrolled Locations (2002).

Pedestrians can legally cross the street at any intersection, whether a marked crosswalk exists or not. To enhance awareness by motorists, install crosswalks on all approaches of signalized intersections. If special circumstances make it unsafe to do so, attempt to mitigate the circumstance.

Curb Extensions Background and Purpose

Curb extensions (also called nubs, bulb-outs, knuckles, or neck-downs) extend the line of the curb into the traveled way, reducing the width of the street. Curb extensions typically occur at intersections but can be used at midblock locations to shadow the width of a parking lane, bus stop, or loading zone. Curb extensions can provide the following benefits:

Curb extensions serve to better define and delineate the traveled way as being separate from the parking lane and streetside. They are used only where there is on-street parking and the distance between curbs is greater than what is needed for the vehicular traveled way.

Related Thoroughfare Design Elements

General Principles and Considerations

General principles and considerations regarding curb extensions include the following:

Diagram showing curb extension, with the following text: Standard curb return without extension limits driver visibility of pedestrians entering crosswalks. The diagram shows a car approaching an intersection with a Driver's Field of Vision indicated.

Figure 10.16 Curb extensions can improve pedestrian visibility and reduce crossing distance. Source: Digital Media Productions.

Photo showing a mid block crossing with a flush curb in New Zealand. Pedestrians are separated from passing vehicles with bollards.

Figure 10.17 A mid block crossing with a flush curb in New Zealand. Pedestrians are separated from passing vehicles with bollards. Source: Community, Design + Architecture.

Photo of an intersection demonstrating use of contrasting material and bollards to delineate the pedestrian and vehicle areas.

Figure 10.18 Use of contrasting material and bollards to delineate the pedestrian and vehicle areas. Source: Kimley-Horn and Associates, Inc.

Recommended Practice

The following practices are recommended when designing curb extensions on urban thoroughfares:

Justification

Curb extensions in unused or underutilized street space can be used to shorten pedestrian crossing distance, increase pedestrian visibility and provide additional space for pedestrian queuing and support activity. Extensions can increase safety, efficiency and attractiveness.

Photo of curb extensions may be used as landscaping or hardscape opportunities. This example shows a retrofit curb extension with drainage retained between the extension and the curb.

Figure 10.19 Curb extensions may be used as landscaping or hardscape opportunities. This example shows a retrofit curb extension with drainage retained between the extension and the curb. Source: Community, Design + Architecture.

Bicycle Lane Treatment at Intersections

Background and Purpose

Selecting appropriate bicycle lane treatments at intersections requires providing uniformity in facility design, signs and pavement markings for bicyclists and motorist safety. The objective is to promote a clear

Related Thoroughfare Design Elements

General Principles and Considerations

General principles and considerations regarding bicycle lane treatment at intersections include the following:

Recommended Practice

The recommended practice for bicycle lane treatment at intersections on urban thoroughfares is shown in Table 10.3.

Justification

At intersections, bicyclists proceeding straight through and motorists turning right must cross paths unless the cyclist moves to the center of the through-right travel lane. Therefore, striping bike lanes up to the stop bar conflicts with this movement. Striping and signing configurations that encourage crossings in advance of the intersection in a weaving fashion reduce conflicts at the intersection and improve bicycle and motor vehicle safety. Similarly, modifications such as special sight distance considerations, wider roadways to accommodate on-street lanes, special lane markings to channelize and separate bicycles from right-turning vehicles, provisions for left-turn bicycle movements and special traffic signal designs (such as conveniently located push buttons at actuated signals or even separate signal indications for bicyclists) also improve safety and operations and balance the needs of both transportation modes when on-street bicycle lanes or off-street bicycle paths enter an intersection.

Bus Stops at Intersections Background and Purpose

Walkable thoroughfare design for bus stops at intersections emphasizes an improved environment for pedestrians and techniques for efficient transit operations. Design considerations for buses are addressed in detail in the section on midblock bus stops in Chapter 9.

Table 10.3 Recommended Practice for Bicycle Lane Treatment at Intersections on Walkable Urban Thoroughfares

Intersection Conditions and Related Recommendations
With pedestrian crosswalks
  • Bike lane striping should not be installed across any pedestrian crosswalks, and, in most cases, should not continue through any street intersections.
With no pedestrian crosswalks
  • Bike lane striping should stop at the intersection stop line, or the near side cross street right-of-way line projection, and then resume at the far side right-of-way line projection.
  • Dash the bike lane prior to the stop line per MUTCD, to warn both motorists and cyclists of the need to prepare for right-turn movements at the intersection.
  • Bike lane striping may be extended through complex intersections with the use of dotted or skip lines.
Parking considerations
  • The same bike lane striping criteria apply whether parking is permitted or prohibited in the vicinity of the intersection.
Bus stop on near side of intersection or high right-turn volume at unsignalized minor intersections with no stop controls
  • A 6 to 8-inch solid line should be replaced with a dashed line with 2-foot dashes and 6-foot spaces for the length of the bus stop. Bike lane striping should resume at the outside line of the crosswalk on the far side of the intersection.
  • In the area of a shared through/right turn, the solid bike lane, if used, should be dashed to the stop bar to indicate that the right-turning motorist should share the space with bicyclists.
Bus stop located on far side of the intersection
  • Solid white line should be replaced with a dashed line for a distance of at least 80 feet from the crosswalk on the far side of the intersection.
T-intersections with no painted crosswalks
  • Bike lane striping on the far side across from the T-intersection should continue through the intersection area with no break. If there are painted crosswalks, bike lane striping on the side across from the T-intersection should be discontinued through the crosswalks.
Pavement markings
  • Bike lane markings should be installed according to the provisions of Chapter 9C of the MUTCD.
  • The standard pavement symbols are one of two bicycle symbols (or the words "BIKE LANE") and an optional directional arrow as specified in the MUTCD. Symbols should be painted on the far side of each intersection. Pavement markings should be white and reflectorized.
Signs
  • Bike lanes should be accompanied by appropriate signing at intersections to warn of conflicts (see Chapter 9B of the MUTCD).
Actuation at Traffic Signals
  • If bike lane extends to the stop bar, provide a detector in the lane and appropriate pavement marking to indicate where the bicyclist should stop.
  • If the bicyclist shares a travel lane, provide a detector (and pavement marking) in the center of the lane.
  • If in-pavement or video detection is not possible, install a push-button on the curb accessible to the bicyclist.

Related Thoroughfare Design Elements

Recommended Practice

Placement of Bus Stops at Intersections

The preferred location for bus stops is the near side or far side of an intersection. This location provides the best pedestrian accessibility from both sides of the street and connection to intersecting bus routes. While not preferred, bus stops on long blocks may be placed at a midblock location or to serve a major transit generator (See Chapter 9). Guidance and considerations related to bus stops at intersections include the following:

It must also contain a loading area of at least 5 feet by 8 feet for wheelchairs to board. (see Chapter 9)

The placement of bus stops at intersections varies from site to site. However, general considerations for the placement of bus stops at intersections include the following:

Table 10.4 summarizes the advantages and disadvantages of far-side and near-side bus stop placements.

Curb Extension Bus Stops (Bus Bulbs)

A curb extension may be constructed along streets with on-street parking. Curb extensions may be designed in conjunction with bus stops to facilitate bus operations and passenger access. The placement of a bus stop on a curb extension should follow the same guidelines as those previously stated (a near-side stop is preferred on two-lane streets where vehicles cannot pass a stopped bus; in the case of a street with multiple lanes where vehicular traffic may pass uncontrolled around the bus, a far-side stop is preferred for sight distance issues).

Table 10.4 Advantages and Disadvantages of Far side and Near side Bus Stops

Far Side Bus Stops
Advantages Disadvantages
  • Minimizes conflict between buses and right turning vehicles traveling in the same direction
  • Minimizes sight distance problems on approaches to the intersection
  • Encourages pedestrians to cross behind the bus
  • Minimizes area needed for curbside bus zone
  • If placed just beyond a signalized intersection in a bus turnout, buses may more easily re-enter the traffic stream
  • If a turnout is provided, vehicle capacity through intersection is unaffected
  • Can better take advantage of traffic signal priority for buses
  • If bus stops in travel lane, could result in traffic queued into intersection behind the bus (turnout will allow traffic to pass around the stopped bus)
  • If bus stops in travel lane, could result in rear-end accidents as motorists fail to anticipate stopped traffic
  • May cause passengers to access buses further from crosswalk
  • May interfere with right turn movement from cross street
  • May obscure sight distance for crossing vehicles
  • If signal priority not in use, bus may have to stop twice, once at signal and then at bus stop
Near Side Bus Stops
Advantages Disadvantages
  • Minimizes interference when traffic is heavy on the far side of an intersection
  • Allows passengers to access buses close to crosswalk
  • Driver may use the width of the intersection to pull away from the curb
  • Allows passengers to board and alight when the bus is stopped for a red light
  • Provides the driver with the opportunity to look for oncoming traffic, including other buses with potential passengers
  • Stopped bus interferes with right turns
  • May cause sight distance problem for approaching traffic, cross-street traffic and pedestrians
  • If located in a pullout or shoulder or at a signalized intersection, a traffic queue may make it difficult for buses to re-enter the traffic stream
  • Prohibits through traffic movement with green light, similar to far side stop without a bus turnout
  • May cause pedestrians to cross in front of the bus at intersections
  • Limits use of traffic signal priorities

Source: Bus Stop Safety and Design Guidelines Manual, Orange County Transportation Authority and Kimley-Horn and Associates, Inc.

 

A bus stop on the near side of a single-lane approach of an uncontrolled intersection should completely obstruct the traffic behind it. Where it is not acceptable to have stopped buses obstruct a lane of traffic and a bus turnout is justified according to the criteria presented in Chapter 9 (section on midblock bus stops), a bus stop may be placed on the far side in the parking lane just beyond the curb extension. It might be appropriate to place a bus stop on a far-side curb extension at an uncontrolled intersection if the warrants for a bus pullout are not met and its placement will not create a traffic hazard.

Near-side curb extensions are usually about 6 feet in width and of sufficient length to allow passengers to use the front and back doors of a bus. A near-side curb extension bus stop is shown in Figure 10.20.

Besides reducing the pedestrian crossing distances, curb extensions with near-side bus stops can reduce the impact to parking (compared to typical bus zones), mitigate traffic conflicts with autos for buses merging back into the traffic stream, make crossing pedestrians more visible to drivers and create additional space for passenger queuing and amenities, such as a shelter and/ or a bench.

Photo of busy intersection with a pedestrian, cars and a bus. This shows a a near-side curb extension bus stop.

Figure 10.20 A near-side curb extension bus stop. Source: Kimley-Horn and Associates, Inc.

In areas where curb extensions are desired, but it is not acceptable to have the bus stop in the travel lane, a far-side pullout area can be created in the parking lane. This location and design eliminates the safety hazard of vehicles passing the bus prior to entering the intersection. However, bus stop length will likely be increased over the normal far-side length because of the need to add an approach taper to the stop downstream from the curb extension.

Queue Jumpers

Queue jumpers provide priority treatment for buses along arterial streets by allowing buses to bypass traffic queued at congested intersections. Queue jumpers evolved from the need to reduce bus delays at intersections or other congested locations. In the past, traffic engineers constructed bus turnouts to move buses out of the traffic stream while they are stopped for passengers. Bus turnouts introduce significant travel time penalties to bus patrons because buses are delayed while attempting to reenter the traffic stream. Queue jumpers provide the double benefit of removing stopped buses from the traffic stream to benefit the general traffic and getting buses through congested intersections so as to benefit bus operations.

Queue jumpers consist of a near-side right-turn lane (buses excepted) and a far-side bus stop and/or acceleration lane. Buses are allowed to use the right-turn lane to bypass traffic congestion and proceed through the intersection. Additional enhancements to queue jumpers could include an exclusive bus-only lane upstream from the traffic signal, extension of the right-turn lane to bypass traffic queued at the intersection, or advanced green indication allowing the bus to pass through the intersection before general traffic does.

Queue Jumper With an Acceleration Lane

This option includes a near-side right-turn lane (buses excepted), near-side bus stop and acceleration lane for buses with a taper back to the general purpose lanes on the far-side of the intersection.

Queue Jumper With a Far-Side Bus Stop

This option may be used when there is a heavy directional transfer to an intersecting transit route. Buses can bypass queues either using a right-turn lane (buses excepted) or an exclusive bus queue jump lane. Since the bus stop is located on the far side, a standard transition can be used for buses to reenter the traffic stream. Queue jumpers at urban thoroughfare intersections should be considered when:

1. High-frequency bus routes have an average headway of 15 minutes or less;

2. Forecasted traffic volumes exceed 500 vehicles per hour in the curb lane during the peak hour and right-turn volumes exceed 250 vehicles per hour during the peak hour; and

3. Intersection operates at an unacceptable level of service (defined by the local jurisdiction).

Works Cited

American Association of State Highway and Transportation Officials. 2004a. A Policy on Geometric Design of Highways and Streets. Washington, DC: AASHTO.

American Association of State Highway and Transportation Officials. 2004b. Guide for the Planning, Design and Operation of Pedestrian Facilities. Washington, DC: AASHTO.

Federal Highway Administration. 2009. Manual on Uniform Traffic Control Devices. Washington, DC: FHWA.

Federal Highway Administration. 2000. Roundabouts: An Informational Guide. Washington, DC: FHWA.

Federal Highway Administration. 2002. Safety Effects of Marked vs. Unmarked Crosswalks at Uncontrolled Locations. Washington, DC: FHWA.

Oregon DOT. Oregon Bicycle and Pedestrian Plan.

Transportation Research Board. 2006. Improving Pedestrian Safety at Unsignalized Crossings, NCHRP Report 562. Washington, DC.

Federal Highway Administration. 2005. Safety Effects of Marked Versus Unmarked Crosswalks at Uncontrolled Locations. FHWA Publication #: HRT-04-100. Washington, DC: FHWA.

United States Access Board. Accessible Public Rights-of-Way. Accessible via www.access-board.gov/prowac/

Sources of Additional Information

American Association of State Highway and Transportation Officials. A Guide to Achieving Flexibility in Highway Design. Washington, DC: AASHTO, May 2004.

American Association of State Highway and Transportation Officials. Guide for the Development of Bicycle Facilities. Washington, DC: AASHTO, 1999.

American Planning Association. Bicycle Facility Planning. Chicago, IL: APA, 1995.

Congress for the New Urbanism. Codifying New Ur-banism. Chicago, IL: American Planning Association, May 2004.

Federal Highway Administration. Flexibility in Highway Design. Washington, DC: FHWA, 1997.

Institute of Transportation Engineers. Innovative Bicycle Treatments. Washington, DC: ITE, 2002.

Insurance Institute for Highway Safety/Ryerson Polytechnic University. Crash Reductions Following Installation of Roundabouts in the United States. March 2000.

Jacobs, Allan. Great Streets. Cambridge, MA: MIT Press, 1995.

Leisch, Joel P. Freeway and Interchange Geometric Design Handbook. Washington, DC: ITE, 2005.

Oregon Department ofTransportation. Main Street— When a Highway Runs Through It, A Handbook for Oregon Communities. Oregon Department of Transportation, November 1999.

Transportation Research Board. NCHRP Report 330: Effective Utilization of Street Width on Urban Ar-terials. Washington, DC: TRB, 1990.

Transportation Research Board. NCHRP Report 500, Volume 3: A Guide for Addressing Collisions with Trees in Hazardous Locations. Washington, DC: TRB, 2003.

Transportation Research Board. NCHRP Report 524: Safety of U-Turns at Unsignalized Median Openings. Washington, DC: TRB, 2004.

Public Rights-of-Way Access Advisory Committee (PROWAAC). Special Report: Accessible Public Rights-of-Way: Planning and Designing for Alterations. 2007.