Past Presidents' Award for Merit in Transportation Engineering: Road Diet Handbook

Jennifer A Rosales
Institute of Transportation Engineers. ITE Journal

Oct 31, 2007 20:00 EDT

INTRODUCTION

Increased traffic volumes on four-lane undivided roadways degrade service and safety. In cities throughout the world, the livability of neighborhoods is improved by putting roadways on road diets. A road diet entails removing travel lanes from the roadway and utilizing the space for other uses and travel modes. Improvements have generated benefits to users of all modes of transportation, including transit riders, bicyclists, pedestrians and motorists.

The focus of the Road Diet Handbook: Setting Trends for Livable Streets is the road diet conversion of four-lane undivided roadways to two-lane roadways plus a two-way left-turn lane by removing a travel lane in each direction (see Figure 1). The remaining roadway width can be converted to bike lanes, on-street parking, landscaping and/or sidewalks. The resulting benefits include reduced vehicle speeds; improved mobility and access; reduced collisions and injuries; and improved livability and quality of life.

The handbook is intended as a comprehensive guide for planners, engineers and designers to help them make decisions on the applicability of road diets. It contains information on planning, analysis, design and implementation, including:

* Results from previous research efforts

* Identification of significant gaps in the field

* Analyses of safety and traffic operations

* Livability considerations

* Case study evaluations

* Lessons learned from experience

* Guidelines for identifying and evaluating potential road diet sites and design concepts, such as typical cross sections

* Overall guidelines for implementation

The handbook also evaluates the livability impacts of road diet projects, addressing issues such as comfort and safety for pedestrians, bicycles and transit users; increased landscaping and beautification opportunities; and improved quality of life and street character.

To determine how specific road diet strategies affect livability, case studies of six sites (Vancouver, WA, USA (two sites); Clear Lake, IA, USA; Athens, GA, USA; Toronto, Ontario, Canada; and Dunedin, New Zealand) were analyzed. At each site:

* A public opinion survey was administered along comparable four-lane undivided and three-lane streets either before or after road diet strategies were implemented.

* Roadway and business activity data were collected both before and after the roadway was converted to further evaluate the livability, safety and operational effects of road diets. The data collected included traffic volumes; vehicle speed and flow characteristics; collision rates and types; congestion; delay and queuing; cross-section design; existence of multimodal facilities; pedestrian crossings; and retail sales activity.

This research represents a state-of-the-practice analysis and provides a snapshot of the current state of the art in the implementation of roadway diets. Ultimately, however, each road diet project is unique to its context, and its designers should strive to make the built, social and natural environments better than before.

HANDBOOK ORGANIZATION

The handbook is divided into four chapters intended to provide guidance on planning, analysis, design and implementation of road diets. The handbook also is intended to provide information on the effects of road diets, including safety, operational and livability benefits. Applicable local ordinances, design requirements and codes must be consulted for impacts to the planning and design process.

Chapter 2: Previous Studies

This chapter summarizes the existing road diet research and literature, including studies of safety and operational impacts of road diets, and includes citations of other literature that can be related to road diets, such as pedestrian crossing safety studies. Gaps in previous research are identified and summarized.

Chapter 3: Case Studies

This chapter includes case study examples of road diet projects that have been implemented at locations around the world. Six sites in the United States and internationally were chosen for the survey and data collection. For each case study, traffic, safety and survey data were analyzed to evaluate factors related to the livability of these streets before and after the road diet was implemented. The methods used to collect and analyze the survey data are described and lessons learned are summarized.

Chapter 4: Practice Guidelines

This chapter helps practitioners identify and evaluate potential road diet candidate sites by taking them through the processes of planning, analysis, design and implementation of road diets. It includes general recommendations for the planning, analysis, design and implementation of road diets that take into account the project context and site-specific conditions. This chapter includes:

* Guidelines for identifying and evaluating potential road diet sites

* General considerations including roadway characteristics and safety, operational and livability benefits

* An evaluation checklist

* Typical cross sections for design concepts

* Implementation strategies

CHAPTER 2: PREVIOUS STUDIES

This chapter summarizes previous research on road diets and includes safety and operational data from these studies. Related research that supports road diets is included in the literature review. An example of such research is Safety Effects of Marked versus Unmarked Crosswalks, by the Federal Highway Administration and the University of North Carolina, which shows that collision rates are significantly higher on multi-lane undivided roadways.1

Safety and operational studies under a variety of traffic volumes and roadway conditions are needed to quantify the conditions for which road diets are appropriate.2 This chapter also identifies gaps in previous research results as well as the significant gap in non-safety benefits, including livability benefits, which have not been examined in past research. This chapter includes past studies on several types of road diet projects and is organized into the following sections:

* Economic effects and walkability

* Safety

* Operations

* Road site project types and examples

* Lessons learned

* Research gaps

CHAPTER 3: CASE STUDIES

This chapter, which illustrates the application of a road diet at six case study locations, includes evaluations of factors related to the livability of the streets at each location. The road diet case studies are diverse geographically and with respect to their surroundings, scale, character, function and form. Six case studies were chosen for the survey and data collection in Dunedin, Toronto, Athens, Clear Lake and Vancouver. They represent a wide range of project contexts, from an urban street in Toronto to a rural street in Iowa, with varying project lengths, designs and magnitude.

Residents and businesses in the vicinity of each case study were surveyed to examine how a road diet affects the livability of an area. The public opinion survey, which was modeled from surveys conducted by Appleyard in Livable Streets, solicited information from people living and working adjacent to the streets with factors directly related to their livability.3 The survey included questions on:

* Household/business characteristics

* Perceptions on the street's traffic, safety, activities (street life) and friendliness

* Recommended improvements

* Reactions to the road diet

The surveys evaluated the livability impacts of road diet projects, addressing issues such as:

* Comfort and safety for pedestrians, bicyclists and transit users

* Increased landscaping and beautification opportunities

* Improved quality of life and street character

The survey medium varied for each case study depending on the case study location and availability of current Web technologies. The surveys were administered either through a door-to-door campaign or using a Web-based survey tool.

The results of the survey were intended to be used as an indication of livability factors for each case study. The local agencies for the case studies were contacted for participation and provided data for the project (see Figure 2).

Fourth Plain Boulevard, Vancouver, WA, USA

Fourth Plain Boulevard is designated as a principal arterial and serves a variety of transportation users, including truck traffic through west Vancouver. Fourth Plain connects Interstate 5 to West Vancouver neighborhoods, recreation and industry, including the Port of Vancouver. Before the road diet project was implemented on Fourth Plain Boulevard, this facility was designated a state truck route. When Fourth Plain was converted, a parallel facility, Mill Plain Boulevard, was converted to a truck route bypass (see Figure 3). This new bypass contributed to the success of the project by removing some truck traffic from Fourth Plain.

Characteristics of the project corridor include the following:

* Average daily traffic (ADT) along Fourth Plain is about 17,000 vehicles, with 1,300 vehicles per hour during the peak hour.

* Posted speed on Fourth Plain is 30 miles per hour (mph) (50 kilometers per hour [km/hr.]).

* The land use adjacent to Fourth Plain is primarily residential and commercial, with residential homes fronting Fourth Plain on the west end.

The purpose of the road diet conversion project on Fourth Plain was to:

* Cost-effectively enhance the environment for all street users while minimizing operational or spillover effects.

* Develop a safe and efficient transportation system.

* Reduce the crash frequency and number along the corridor.

* Improve pedestrian and bicycle mobility.

* Establish a balance between vehicle operations, port freight access and neighborhood livability.

Livability Survey. In April 2004, an online Web survey was used to solicit public input on livability. Most of the respondents were pleased with the results of the road diet project on Fourth Plain Boulevard and noticed improvements to traffic, safety and livability. The handbook provides complete survey findings for each case study.

Retail sales analysis found that the commercial area on, adjacent to and near the Fourth Plain Boulevard road diet project performed better than comparable areas in the city.4 This growth occurred after the implementation of the road diet project and during a recession that affected all portions of the city. When comparing gross receipts before and after the road diet project, the commercial area in the Fourth Plain project area had a positive increase of 3.1 percent compared to negative declines of -9.8 percent to -25 percent in two other comparable community commercial zones in the city.

Lessons Learned.

* Safety improvements resulted from the implementation of the road diet with a significant reduction in crashes.

* Traffic along Fourth Plain Boulevard continued to operate adequately without queuing issues and with improved operations for bicyclists and pedestrians.

* From the livability survey, the majority of the respondents concluded that the road diet improved traffic issues.

* The livability survey suggests that the implementation of a road diet creates a street environment that is calmer and safer, although respondents don't treat the street as a residential street (for example, not letting their children play in the street).

Baxter Street, Athens-Clarke County, GA, USA

Baxter Street is located in Athens and is classified as an arterial that connects the University of Georgia on the east to a major shopping center on the west. Baxter Street runs parallel to State Highway 78 and serves a variety of transportation uses. Characteristics of Baxter Street include the following:

* ADT is 18,000 to 20,000 vehicles, with 1,500 vehicles per hour during the peak hour.

* Posted speed is 35 mph (55 km/hr.).

* Three bus routes serve 10 bus stops along its road diet section.

* The land use is primarily commercial along Baxter Street with residential and university facilities in the surrounding project area. The community in the project area is highly educated.

The road diet project started as a safety demonstration project when Baxter Street needed resurfacing. The purpose of the project was to:

* Reduce the crash frequency along the corridor (especially rear-end and sideswipe).

* Increase travel flow by separating through vehicles from left-turning vehicles.

* Designate an area within the roadway for bicycle travel.

* Further separate vehicles from the sidewalk edge.

Baxter Street has a 40-foot (12-meter) right of way (see Figure 4). The before and after dimensions are as follows:

* Before the road diet, the facility consisted of four 10-foot-wide (3-meter) lanes.

* After the road diet, the facility consisted of two 14-foot-wide (4.2-meter) lanes to be shared between vehicles and bicycles and one 12-foot-wide (3.6-meter) two-way left-turn lane.

In the initial design, Baxter Street was considered too narrow for full bike lanes, so the 14-foot travel lanes were striped with a dashed line to create an 11-foot travel lane and 3-foot shared vehicle/bike lane. In 2003, the 3-foot shared areas were striped as bicycle-use-only lanes.5

Livability Survey. An online Web survey was chosen for this case study to solicit public input to the livability survey. The majority of respondents indicated that the street width and the number of travel lanes was "just right." Most also indicated that the street was "safe," "very safe," or "comfortable." This response indicates that the road diet project resulted in a positive change. The handbook provides complete survey findings for each case study.

Lessons Learned. After the implementation of the Baxter Street road diet, Athens-Clarke County staff recommended the following for road diet projects:6

* Add bus pull-out bays so buses do not block through traffic.

* Include access management plans with appropriate spacing and/or eliminate driveways to reduce conflict points.

* Improve grates across catch basins to improve bike operations (for example, improve stormwater collection systems to remove water from curb lanes where bikes travel).

* Repair sidewalks and driveways in poor condition.

* Improve landscaping to "soften" the corridor.

* Coordinate with other corridor improvements.

U.S. 18, Clear Lake, IA, USA

U.S. 18 is a state highway in Iowa and the primary east-west route through the City of Clear Lake. Railroad tracks run parallel to U.S. 18 on the south side. U.S. 18 serves traffic traveling in, through and out of Clear Lake and a variety of transportation uses in Clear Lake, including freight movement. U.S. 18 provides access to the downtown business and tourist area. Characteristics of U.S. 18 include the following:

* ADT is approximately 12,000 vehicles per day, with 1,200 vehicles per hour during the peak hour.

* Posted speed is 45 mph (70 km/hr.).

* Sidewalks do not exist in the project area.

* Land use is primarily commercial, with residential, commercial and recreational uses adjacent to the project area. U.S. 18 provides access to a disabled care community and facility.

The U.S. 18 road diet project consisted of simply re-striping the highway with the road conversion, installing one traffic signal and upgrading an existing traffic signal. A second phase of the project will include the installation of right-turn lanes at key intersections along the corridor. Before the conversion, U.S. 18 was a four-lane undivided roadway. It was converted to two lanes plus a two-way left-turn lane and painted shoulders. The purpose of this project was primarily to improve safety along the corridor.

Livability Survey. A door-to-door survey method was used for the U.S. 18 case study to solicit public input to the livability survey. The respondents indicated that they would like more lanes to travel faster and to relieve some congestion during the peak hour. However, these respondents also thought that speeding remained a problem at times. The respondents wanted to see more police enforcement to slow speeds and keep motorists from using the center turn lane as a passing lane. The handbook provides the survey findings for each case study.

Lessons Learned. The project was implemented primarily to improve safety, and an assessment of crash statistics indicates that safety has improved. However, many respondents believed that the road was less safe following the initial phase of the road diet implementation. There may be a number of reasons for this perception, including unclear lane striping, misuse of the center turn lane and several complementary improvements still to be added to the project, including improved signal timing and right-turn lanes. Depending on the level of community acceptance of the project, a public involvement/education effort may be beneficial to show the resulting safety benefits of the project.

The cost of a road diet project can be minimal by simply re-striping a roadway, and it can be completed as an interim solution or as a pilot project for a short length of time, such as 6 months. By implementing a road diet as a pilot project study, the effects on safety and operations can be measured before deciding whether to keep it permanendy and/or whether to fund enhanced design features and a more permanent solution. When evaluating a temporary solution, it is important to note that it may not provide all of the benefits of a permanent solution.

On U.S. 18, the transition areas from the four-lane to two-lane section with a two-way left-turn lane was confusing for drivers, and the survey respondents indicated that better lane markings were needed. A lesson learned for a pilot project or re-striping project is to ensure that lane markings are clear and that old lane markings are not still visible. Both the road diet pilot project and the interim solution can be enhanced by adding landscaping, signal timing improvements, sidewalk connectivity, improved pedestrian crossings and other enhanced design features.

St. George Street, Toronto, Ontario, Canada

St. George Street, a multimodal street through the St. George campus of the University of Toronto, was put on a road diet in the 1990s. St. George Street is classified as a minor arterial road by the City of Toronto and serves vehicles, delivery trucks, bicyclists, pedestrians and even skateboarders. An extremely high number of pedestrians use St. George Street, and continuous sidewalks on both sides of die street are provided in the pedestrian zones. The ADT along St. George Street is about 7,400 vehicles, with approximately 700 vehicles per hour during the peak hour. The posted speed on St. George Street is 25 mph (40 km/hr.).

The St. George Street road diet project was completed in 1996, about 8 years before this study. The project was enhanced incrementally beginning in 1993, with the most significant construction occurring in 1996. Prior to 1993, the street operated as a four-lane road during peak hours and as a two-lane road with on-street parking permitted during non-peak hours.

In 1993, the number of lanes on St. George Street was reduced to two by permitting parking during all hours. Bicycle lanes, a narrow painted median and turn lanes were provided at key intersections as part of the lane reduction project. The road diet project also narrowed the pavement width and reconstructed the curbs along St. George Street in 1996. Before the road diet project, the pavement width was wide considering the street function and surroundings. As part of the road diet project, the pavement width was narrowed from 46 feet (14 meters) to a varying width of 31 to 40 feet (9.5 to 12.2 meters). The sidewalk area was widened to increase the pedestrian zone.

The narrowing of the pavement and widening of the sidewalk significantly enhanced pedestrian crossing areas. The majority of pedestrian crossings occur at uncontrolled mid-block locations that correspond to campus pedestrian routes. Alternative roadway pavement materials were used to highlight mid-block crossing areas. Curb extensions at specific locations in coordination with on-street parking have reduced vehicle travel speeds. By narrowing the pedestrian crossing areas, pedestrians have been encouraged to cross at specific locations with shorter crossing distances. Landscaping has been added to provide a buffer and enhanced urban environment to the road diet project. Figure 5 provides photographs of St. George Street.

Livability Survey. A Web survey was used to solicit public input on the livability of the street. Survey respondents indicated satisfaction with the street width and number of lanes, but some respondents indicated a desire to remove all cars. Survey respondents recognized the benefits the road diet project produced, including slower speeds and improved safety, but still desired further improvements such as more crosswalks and more greenery. The respondents desired additional aesthetic enhancements such as greenery and replacement of concrete planters, cobblestones and pavers. The handbook provides complete survey findings for each case study.

Lessons Learned. A road diet project through an urban university setting has both perceived benefits by users of all transportation modes as well as actual measured safety and operational benefits. An urban university environment is an ideal location to consider a road diet project because of the high number of pedestrians and bicyclists who benefit from projects of this type.

Kaikorai Valley Road, Dunedin, New Zealand

Kaikorai Valley Road is located in Dunedin, an eastern coastal city in New Zealand. Kaikorai Valley Road is classified as a regional arterial road, defined by the Dunedin City District Plan as one that serves as a link of strategic importance between or within regions and between districts. It serves as an alternate route into and out of the Dunedin central business district from the south and serves a variety of transportation uses. Parking is provided on both sides of the road. The average daily traffic along Kaikorai Valley Road is about 10,000 vehicles per day, with approximately 1,000 vehicles per hour during the peak hour.

The road diet project on Kaikorai Valley Road was completed in 2003, about one year before this study. The length of the road diet project was 2.4 km (1.5 miles), on the northern end of section two of Kaikorai Valley Road. The road diet project entailed reducing the road (section two) from a four-lane roadway with on-street parallel parking to a twolane roadway with on-street parking and cycle (bicycle) lanes (see Figure 6). The project included:

* Planting the existing median with low growing shrubs

* Improving pedestrian crossings by converting a crossing to a pedestrian crossing point, constructing disabled crossing ramps and installing floodlighting

* Upgrading an existing pedestrian crossing by installing floodlighting

* Extending the length of turn pockets to accommodate queuing vehicles without impeding the flow of through traffic

Livability Survey. A door-to-door survey method was used for the Kaikorai Valley Road project to solicit public input to the livability survey. Respondents had mixed perceptions regarding the results of the project, but almost half recommended this project for other streets in the city. The handbook provides complete survey findings for each case study.

Lessons Learned. The following summarizes the lessons learned for the Kaikorai Valley Road case Study:

* The road diet resulted in safety improvements for all transportation modes, with a significant reduction in traffic speeds and crashes.

* Traffic continued to operate adequately with no traffic diversion impacts.

* From the livability survey, the majority of the respondents on Kaikorai Valley Road concluded that the road diet resulted in positive transportation improvements.

Grand Boulevard, Vancouver, WA

This case study differed from the others in that the roadway was surveyed before die implementation of a road diet project. Grand Boulevard, an undivided four-lane arterial located in the City of Vancouver, is an example of an ideal road diet candidate. The City of Vancouver has been challenged by neighborhoods and special interest groups to re-assess the operational and capacity needs on many undivided four-lane corridors. The motivations behind these requests are varied, and often revolve around the perceived trade-off between transportation capacity and community livability.

Livability Survey. Overall, the survey respondents seemed as or more concerned with non-traffic issues such as aesthetics and crime. Perceptions of safety were correlated with perceptions of traffic speed; respondents who felt the street was unsafe tended to say that traffic moved too fast. The handbook provides complete survey findings for each case study.

Recommendations. Grand Boulevard is an ideal facility for a road diet project, and the City of Vancouver plans to convert it to a two-lane with center left-turn lane facility as funding becomes available. The City of Vancouver plans to study Grand Boulevard after the road diet project is constructed to evaluate its effectiveness. Recommendations for a road diet project on Grand Boulevard include die following:

* Re-stripe the roadway from a four-lane roadway to a two-lane roadway with a center left-turn lane or median channelization (minimum 11-feet width for center turn lane).

* Provide a dedicated bike lane in both directions.

* Institute a speed monitoring and enforcement program to reduce vehicle speeds.

* Improve pedestrian facilities by adding curb ramps, crosswalks, lighting and sidewalks where needed to provide connectivity, comfort and safety.

* Implement the road diet project with pavement overlay of street.

Case Studies Summary

Safety. Significant safety benefits resulted from the road diet projects (see Figure 7). The overall number of crashes was reduced in the range of 10 to 65 percent. Also, traffic speeds were reduced at the case study locations as a result of the road diet projects. The safety impacts of the road diet case studies are summarized as follows.

On Fourth Plain Boulevard, the following safety impacts resulted:7

* The number of reported collisions along Fourth Plain decreased by 52 percent after the road diet project was constructed.

* Pedestrian safety improved. There were no reported pedestrian collisions along Fourth Plain after the road diet project compared to six reported pedestrian collisions for the three years prior to the road diet project.

* Traffic speeds along Fourth Plain decreased about 18 percent after the road diet project was constructed, from 29.4 mph to 24.2 mph.

On Baxter Street, the road diet project resulted in the following safety impacts:8

* The reported number of crashes was reduced by 53 percent from the implementation of the road diet project.

* The reported number of crashes at unsignalized locations was reduced by 60 percent.

* The number of rear-end crashes was significantly reduced by 45 percent because left-turning vehicles had a center turn lane to use instead of stopping in the dirough lane.

On U.S. 18 in Clear Lake, the safety impacts resulting from the road diet project included the following:9

* Number of crashes per year decreased by 65 percent from 40 crashes per year to 14 crashes per year after the project was implemented.

* Travel speeds were reduced with before and after speed data showing a 52-percent reduction in aggressive speeding. In addition, the number of vehicles driving over the speed limit was reduced by 32 percent.

On St. George Street, significant safety improvements were realized as a result of the road diet lane reduction and narrowing project:10

* The number of collisions was estimated to be reduced by about 40 percent, from about 33 collisions per year before the lane reduction to about 20 collisions per year after.

* By narrowing the pavement and lane widths on St. George Street, the number of collisions was further reduced to about 19 collisions per year for die six years following the pavement and lane width narrowing.

On Kaikorai Valley Road, safety benefits were also achieved:11,12

* The road diet project on Kaikorai Valley Road resulted in a 30-percent crash reduction, from 10 crashes per year before the road diet project to about 7 crashes per year after.

* Traffic speeds along Kaikorai Valley Road were also reduced. Approximately 88 percent of the speeds before the road diet project exceeded 50 km/hr. (30 mph) compared to approximately 69 percent of the speeds after the road diet project.

Despite the diverse settings, in all five case study sites where the road diet was implemented, die number of crashes and measured speeds decreased, resulting in significant safety improvements.

Operations. As shown from the case studies, there were no significant changes to traffic volumes on the road dieted streets. In addition, no significant traffic diversion impacts were found. The road dieted streets continued to operate adequately without significant queuing and operational impacts. For several road diet projects, pedestrian and bicycle activities were measured and observed. Improved pedestrian and bicycle conditions resulted.

On Fourth Plain Boulevard, the traffic operational impacts after the road diet project implementation were as follows:13

* No significant negative impacts to traffic operation; no reports of queuing vehicles interrupting adjacent business and residential access on Fourth Plain Boulevard.

* Bicyclists and pedestrian activity increased. The bicycle operational safety along the corridor improved, and the bicycle level of service improved significantly since the road diet project was implemented.

* Other operational benefits, such as the bicycle lane providing space for police enforcement and a refuge area for vehicles temporarily broken down.

* There was no significant traffic diversion as part of the Fourth Plain Boulevard road diet project.

On Baxter Street, the traffic operational impacts resulting from the road diet project were as follows:14

* No significant impacts to the traffic volumes on Baxter Street or on adjacent streets after the road diet conversion project.

* Traffic diversion experienced from the project was about 4 percent of the Baxter Street traffic to Broad Street, a parallel arterial street north of Baxter Street.

After the road diet project, the traffic operation along U.S. 18 remained acceptable with good mobility. The resultant operating speeds were more uniform and closer to the posted speed limit.15

On St. George Street, the road diet project resulted in the following traffic operational impacts:16

* Adequate traffic operations along St. George Street.

* Increase in pedestrians and bicyclists.

* Traffic volumes along St. George Street remained relatively consistent before and after the narrowing of the travel lanes as part of the road diet project, from 7,300 vehicles per day in 1994 to about 7,400 vehicles per day in 2003.

* No traffic diversion impacts.

On Kaikorai Valley Road, the traffic operations resulting from the road diet project were as follows:17

* Adequate traffic operations along Kaikorai Valley Road.

* Traffic volumes were not impacted from the road diet project and remained relatively constant. In addition, the vehicle classification and percent of trucks remained relatively constant.

* Traffic volumes showed a small amount of growth, which indicates that traffic diversion was not experienced from the road diet project on Kaikorai Valley Road.

At all locations, impacts to overall traffic operations were negligible, if not positive.

Lessons Learned. The following section summarizes the lessons learned from the road diet case studies:

* Consider road diet projects when multiple opportunities arise, such as a pavement reconstruction project, presence of an adjacent parallel route and jurisdictional roadway transfer.

* Consider community requests to evaluate and implement road diet projects. With technical evaluation and community involvement with stakeholder groups, road diet projects are more likely to be successful.

* A public education campaign that goes along with a road diet project needs to emphasize the notion that this is a safety enhancement project and that it may require trade-offs in capacity and speed. Increase public education regarding the use of the two-way leftturn lane.

* Manage community expectations with clear communication and documentation. Identify project goals, performance measures and expectations and conduct follow-up evaluation.

* Coordinate road diet projects with concurrent pavement overlay projects, if possible. A road diet striping plan on new pavement results in less driver confusion.

* By implementing a road diet as a pilot project study, the effects on safety and operations can be measured before deciding whether to keep it permanently and/or whether to fund enhanced design features and a more permanent solution. A temporary solution may not provide all of the benefits that a permanent solution would provide.

* Add bus pull-out bays when needed.

* Include access management plans with appropriate spacing and/or elimination of driveways to reduce conflict points.

* Improve stormwater grates across catch basins to improve bike operations.

* Repair sidewalks, ramps and driveways in poor condition.

* Improve landscaping to "soften" the corridor.

* Coordinate with other corridor improvements.

* Install a grass median or other median treatment.

* Increase police enforcement of speeds and the proper use of the center turn lane.

Both the road diet pilot project and interim solution can be enhanced by adding landscaping, signal timing improvements, sidewalk connectivity, improved pedestrian crossings and other enhanced design features.

The implementation of a road diet project can result in safety, operational and livability benefits for all modes of transportation.

CHAPTER 4: ROAD DIET GUIDELINES

Road diets, when implemented properly and in the appropriate context, can enhance the livability of a street and contribute to the traits that can make a street great. This chapter provides guidance to the practitioner regarding how to determine if a street is a good candidate for a road diet and best practices for road diet implementation.

When determining the appropriateness of a road diet conversion project, the project context and site-specific conditions such as traffic flow characteristics, vehicle capacity, traffic operations, safety, environmental impacts (social, built and natural) and livability need to be considered.

This chapter will help practitioners identify and evaluate potential road diet candidate sites by taking them through the processes of planning, analysis, design and implementation of road diets. It includes general recommendations for road diets that take into account the project context and site-specific conditions that need to be considered. This chapter includes:

* Guidelines for identifying and evaluating potential road diet sites

* Feasibility factors

* Design guidelines and considerations

* Typical cross-sections for design concepts

* "Greening" road diet options

* Other considerations

Identification and Evaluation of Potential Road Diet Candidates

A road diet project can improve walkability and community livability and economics. The road diet is an alternative to widening the cross section of roadway and, when appropriate, it can have lower overall impacts than widening the roadway, can be a more cost-effective option and can result in acceptable operations and improved safety.

Recent research has recommended that road diet conversion be evaluated in terms of safety and operation effects, especially vehicle speeds, congestion, traffic volume and traffic flow. Road diet conversions should be made on a case-by-case basis considering traffic flow, vehicle capacity and safety goals.18 Each potential road diet implementation should identify, compare and analyze all feasible alternative improvements that meet the project goals and objectives.

Feasibility Factors

Several feasibility factors were identified in research conducted by Knapp to evaluate the feasibility of road diets:19

* Roadway function and environment

* Overall traffic volume and level of service

* Turning volumes and patterns

* Frequent-stop and slow-moving vehicles (agriculture, buses, mail, buggies)

* Weaving, speed and queues

* Crash types and patterns

* Pedestrian and bicycle activity

* Right-of-way availability, cost and acquisition impacts

* Presence of parallel routes

* Other contextual considerations

Road Diet Design Solutions

This section in the handbook provides a toolbox for design of road diet projects, including optional enhancements such as landscaped medians; improvements to pedestrian crossings and facilities; street trees and curbside planters; improved transit user facilities; and green street options. For cost-effectiveness and natural resource conservation, road diet projects can be designed and constructed by simply re-striping the roadway and re-using the existing pavement width and curbs.

A context-sensitive solutions approach is recommended for potential road diet projects. From "Thinking beyond the Pavement," Maryland State Highway Administration Workshop, 1998:

Context sensitive design asks first about the purpose and need of the transportation project, and then equally addresses safety, mobility, and the preservation of scenic, aesthetic, historic, environmental, and other community values. Context sensitive design involves a collaborative, interdisciplinary approach in which citizens are part of a design team.

It is important to recognize that every project is unique. Design solutions for road diet project alternatives need to:

* Provide a safe and efficient transportation corridor for vehicles, buses, bicycles and pedestrians.

* Balance the needs of the transportation system with the interests of the surrounding community and the environment.

* Create a transportation facility that is an asset to the community.

Road diet project objectives could include:

* Improved safety and operations

* Enhanced neighborhood character

* Improved access to businesses, transit, parks, etc.

* Preserved and improved environmental conditions throughout project limits by reducing pavement area and treating water run-off

Design Concepts

Street design is a key element of smart growth development and direcdy affects quality of life. Designers are encouraged to integrate streets closely with planned fand use. From Metro's (regional government agency for Portland Metro, OR, USA) document, Creating Livable Streets:20

A livable regional street should provide those environmental conditions that support independence and freedom of choice; provide orientation, safety and comfort; encourage a sense of community yet provide sufficient privacy; foster a sense of neighborly ownership and responsibility; avoid disturbing nuisances; and enhance the economic value of adjacent property.

The road diet design concepts presented in this chapter are focused on the conversion of a four-lane undivided roadway to a two-lane roadway. A center turn lane is recommended when driveways are present, and a landscaped center median in areas where driveways are uncommon or absent. The remaining roadway width can be converted to bike lanes, on-street parking, landscaping, sidewalks and/or turned back to the property owners.

A Policy on the Geometric Design of Highways and Streets (the Green Book), published by the American Association of State Highway and Transportation Officials (AASHTO) provides geometric design criteria for roadways. As noted in the Foreword:

The intent of this policy is to provide guidance to the designer by referencing a recommended range of values for critical dimensions. It is not intended to be a detailed design manual that could supercede the need for the application of sound principles by the knowledgeable design professional Sufficient flexibility is permitted to encourage independent designs tailored to particular situations.21

The road diet design concepts presented in the handbook complement the AASHTO guidelines.

Traveled Way

The handbook provides general design parameters for major urban arterial and collector thoroughfares with varying contexts. General guidance on dimensions and cross-section elements criteria, including lane widths, is included for urban streets with two to four through lanes.

Travel lane and turn lane widths can vary depending on the project context, land use, modal use and speed, from a minimum of 10 feet to 14 feet (3 meters to 4.3 meters).

Suggested Left-Turn Treatments for Road Diet Streets

Based on previous research, the handbook provides guidance on the selection of left-turn treatments for specific conversion alternatives and factors.

Transitions

When the number of travel lanes is reduced and/or width of the street is changed, a smooth transition needs to occur. The principles for designing effective transitions include:22

* Properly design, stripe and sign geometric transitions using established guidance {Manual on Uniform Traffic Control Devices [MUTCD]).

* Transitions should occur on a tangent roadway section and avoid areas with horizontal and vertical sight distance constraints.

* The entire transition length should be visible to the driver.

* When roadways widen or lanes are added, a transition taper of 10:1 is sufficient.

* Transitions to left- or right-turn lanes typically require a shorter taper. AASHTO recommends 100 feet (30.5 meters) for single-turn lanes.

It should be noted that choosing the transition locations for road diet projects needs special attention and thorough evaluation. Major driveways and intersections should be avoided along a transition. Intersection and roundabout locations can be ideal beginning transition locations to drop lanes.

Bicycle Facilities

Bicycle travel is an important element of multimodal, livable streets. Bike lanes are practical and often essential for road diet projects. They not only improve the bicycling environment, but also provide a buffer to pedestrians (see Figure 8). In addition, bike lanes allow space for vehicles to temporarily store while emergency vehicles pass, add to turning radii and improve sight lines. Important sources for bicycle facility design and treatments are the AASHTO Guide for the Development of Bicycle Facilities, ITE Innovative Bicycle Treatments and MUTCD.23,24,25

General considerations for bicycle facilities include the following:

* Smooth surfaces are needed for the safety and comfort of bicyclists.

* Regular maintenance and street sweeping are required, and pavement should be free of large cracks and potholes.

* Curb inlets for drainage or bicyclesafe inlet grates should be provided.

Recommended lane widths and typical lane markings for bicycle lanes are presented in the handbook.

On-Street Parking

On-street parking provides a buffer to pedestrians from traffic and is found to decrease traffic speeds. In addition, on-street parking meets the needs of adjacent land uses and stimulates street activity. On-street parking should be implemented based on project context, traffic volume and speed; adjacent land uses; and local parking management plans and policies. General considerations for on-street parking are:26

* Parallel parking should be considered on urban arterials and collectors.

* Angled parking may be considered on low-speed and low-volume commercial collectors and main streets.

* On-street parking should not be considered on major streets with speeds greater than 35 mph due to potential maneuvering conflicts.

* Consider the use of a curb lane for on-street parking during off-peak hours when traffic capacity needs to be balanced with on-street parking needs.

* Provide a minimum 1.5-foot (0.46-meter) offset between face of curb and edge of potential obstructions such as poles and trees.

* Parking should be prohibited within 20 feet (6.1 meters) of fire hydrants or per local codes.

* Parking should be at least 20 to 50 feet (6.1 to 15.2 meters) from mid-block crosswalks and at least 20 feet (6.1 meters) from the curb return of intersections (30 feet [9.1 meters]) for signalized intersections). Curb extensions can be used to reduce this distance.

Pedestrian Realm

Streets have multiple uses, and appropriate solutions should be selected to improve pedestrian safety and access. In addition, walkable streets promote healthy communities and safe neighborhoods. Sidewalks are important elements of street design (see Figure 9). Key attributes of good sidewalk corridors are:27

* Accessibility

* Adequate travel width

* Safety

* Continuity

* Landscaping

* Social space for people to interact

* Quality of place to strengthen the character of neighborhoods and business districts

When implementing a road diet conversion project, the following are key issues/actions to be addressed and/or undertaken:

* Identification of pedestrian crossing locations and exposure to potential hazards.

* Identification of missing sidewalks or pathways.

* Identification of transit zones and stop locations and provision of adequate pedestrian access.

* Both pedestrian and bicycle facilities designed to be compatible with and facilitate transit use.

* Design and maintenance of landscaping to provide good visibility between pedestrians and approaching vehicles.

* Provision of adequate lighting for pedestrian safety at night.

* Comfortable sidewalks for pedestrians, with a minimum width of 5 feet, and routinely maintained.

Other sources for effective design of pedestrian facilities include: ITE's Alternative Treatments for At-Grade Pedestrian Crossings; Safety Effects of Marked versus Unmarked Crosswalks at Uncontrolled Locations for FHWA; ITE's Design and Safety of Pedestrian Facilities; and AASHTO's Guide for Planning, Design and Operation of Pedestrian Facilities.28-31 Pedestrian facilities need to be accessible to all users and, in the United States, meet the requirements of the Americans with Disabilities Act.

An additional resource is the U.S. Access Board's Draft Guidelines for Accessible Public Rights-of-Way.32 Guidelines for installing marked crosswalks and other needed pedestrian improvements at uncontrolled (unsignalized) locations are provided in the handbook. To reduce the effective street crossing distance for pedestrians, the following design options can be considered:

* Narrow the street width;

* Provide curb extensions (see Figure 10); and/or

* Add raised pedestrian refuge islands at intersections.

Pedestrian refuge islands as raised medians can be added at intersections between center left turn lanes, if designed appropriately.

Typical Road Diet Cross-Sections (Two-Lane Streets)

Several road diet cross sections are provided in the handbook for reference. The selection of cross sectional elements is project-specific. The width of street, travel lanes, bike lanes, on-street parking, sidewalk and landscape areas can be adjusted within the right-of-way (see Figure 11). These decisions will likely be based on modal priorities, adjacent land uses and speeds, should be made on a case-by-case basis and may vary along a project corridor.

Streetscaping may be initiated by a community visioning or planning process that establishes guidelines for streetscape design. Implementation may involve special published guidelines, plans and funding for streetscape improvements on a particular street or in an area.

Streetscape improvements can also be incorporated into subdivision and roadway design standards, for example, by encouraging or requiring shorter blocks, wider sidewalks, bike lanes, narrower streets, landscaping and other features that improve accessibility, walkability and aesthetics.

Traffic Calming Options

Traffic calming measures can be implemented as part of road diet projects. The ITE Traffic Calming State of the Practice provides traffic calming options that can be considered.33 The handbook presents examples of traffic calming measures. In addition, roundabouts can be used for intersection traffic control to both slow traffic speeds and keep traffic moving. FHWAs Roundabouts: An Information Guide is an important resource to use when considering the implementation of a roundabout.34 Roundabouts have also been used to serve as transition points between three- or two-lane street segments and four-lane segments.

Green Streets

A green street meets the transportation need and applies environmental stewardship to improve the natural, built and social environments (see Figure 12). A few examples of green street design solutions are provided in this chapter of the handbook as optional enhancements for the road diet application.

As identified in Metro's (regional government agency for Portland Metro) Green Streets Handbook, the appropriate green streets design solutions and/or combination of solutions depends on the desired functions (e.g., runoff reduction, detention, retention, conveyance and water quality mitigation) and site/watershed conditions.35

ACKNOWLEDGMENTS

This research was funded by the PB William Barclay Parsons Fellowship.

© 2007 Institute of Transportation Engineers Provided by ProQuest LLC. All Rights Reserved.

Source: Institute of Transportation Engineers. ITE Journal