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Publication Number: FHWA-HRT-04-091
Date: August 2004
Signalized Intersections: Informational Guide
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CHAPTER 5 — PROJECT PROCESS
TABLE OF CONTENTS
LIST OF TABLES
5. 0 Project Process
This chapter describes a standard process for conducting an intersection design/redesign project. During the initial stages of a project, stakeholders are identified, the scope of analysis is determined, data are collected, and key issues of concern are identified. From this information, a problem statement is developed and potential countermeasures or treatments are identified. In the alternatives evaluation stage, potential treatments are evaluated for feasibility and effectiveness. After a treatment is chosen, the improvement is implemented and monitored over time. This chapter describes a general thought process to guide readers to issues to consider and questions to ask.
5.1 Project initiation
An intersection project typically begins with notification to a lead engineer. The engineer could be a city, county, or State traffic engineer responding to a concern raised by the public, a supervisor, a planning commission, or a city council. In other cases, the lead engineer may be a consultant responding to a request for proposal for a particular intersection design project. During this process, the lead engineer should gather initial information that will lead to identification of problems. Information should be gathered through stakeholder interviews, review of existing data, and field visits as described in the following sections.
Two questions that should be asked at the outset of the process are:
New intersections typically afford greater flexibility for design and the selection of treatments than do existing ones. Existing intersections are often constrained by utility placement, presence of development surrounding the intersection, and issues related to construction and to maintenance of traffic. The effect of a treatment at an existing location must take into account the effect on user expectancy. Changes to way-finding, lane geometry, and traffic control may result in confusion and, in turn, create a safety deficiency.
Determining whether an intersection condition is part of a system problem is an important consideration when evaluating intersection treatments. For certain cases, a capacity improvement to an intersection may provide little benefit if the constraining point on the system is located upstream or downstream of the intersection. Likewise, implementing an improvement such as a turn movement restriction may solve an operational or safety problem at the subject intersection, but may result in the migration of the problem to a new location. These system effects must be considered at each step in the treatment evaluation and selection process.
5.2 Identify Stakeholder interests and objectives
Each project should begin by identifying the affected stakeholders and conducting stakeholder interviews to define interests, goals, and objectives. Stakeholders include any person or group affected by a project: users of the facility (motorists, pedestrians, bicyclists, etc.); adjacent property owners and residents; jurisdictional owners and managers of the facility; and decisionmakers who have influence over making improvements to the facility.
The interest range of stakeholders is widespread: A local business owner may be solely concerned with maintaining access for his/her business; a neighborhood group may want pedestrian treatments to improve the safety for a pedestrian crossing; and a traffic engineer may want to maximize throughput on the mainline facility. a planning commission may recommend yet another treatment based on concerns raised from its constituents.
It is important to highlight the interests of all stakeholders and clearly define their goals and objectives early in the process. This includes defining jurisdictional policies and standards regarding the safety and operations of the intersection. Stakeholders’ goals and objectives need to be considered carefully and acknowledged at each step of the process, and should be tied to performance measures to provide a means for evaluation.
5.2.1 Intersection Users
Intersection users include motorists, pedestrians, bicyclists, and transit riders (see chapter 2 for a more complete discussion of user types). These users may be categorized in subgroups with similar concerns and issues (e.g., citizens from a neighborhood group, disabled persons, truck drivers).
It is important to understand how the goals and objectives of each user group relate to each other, and the tradeoffs that exist between them. For example, lane-widening improvements that are implemented to solve an operational deficiency for motorists may reduce the safety and quality of service for pedestrians due to the number of conflicts added and the increased crossing distance. In some cases, the benefits experienced by one user group may be offset by the negative impacts imposed on another.
5.2.2 Adjacent Property/Business owners
The access and circulation needs for adjacent properties and business owners should be addressed based on an evaluation of the land use, traffic demand, and access needs of each site. Air quality and noise impacts to adjacent properties and businesses are also important consideration when evaluating improvement alternatives.
5.2.3 Facility Managers
Stakeholders include the owners and managers of the facility such as state departments of transportation engineers and city and county planning and public works staff. Facility managers typically are expected to meet an adopted standard or policy for the facility. As part of the stakeholder identification process, relevant and adopted documents such as state highway plans, comprehensive plans, and transportation system plans should be reviewed to identify the transportation standards and policies in place that may affect the study intersection. In addition, jurisdiction officials should be contacted and interviewed to identify plans for system improvement that may affect the characteristics or demand patterns at an intersection.
5.2.4 Other Decisionmakers
It is also important to consider other decisionmakers in addition to local jurisdiction officials, including technical advisory committee members, steering committee members, planning commissioners, city councilors, and other government officials. It is important to gain an understanding of the criteria that each of these decisionmakers uses in evaluating recommendations and making decisions. Driving forces may include local policy, local politics, agencies/organizations represented, and level of ownership and commitment to the project.
A summary of the key concerns and issues of each stakeholder should be prepared and circulated to relevant project team members to ensure that everyone has a clear understanding of the constraining factors of a project. Table 19 provides an example of cataloging stakeholder interests and objectives.
Table 19. Example stakeholder interests and objectives.
5.3 Data Collection
Data acquisition and field investigation provides an understanding of the physical and operational characteristics of the study intersection and identify factors that contribute to its deficiencies. All information required for analysis and evaluation should be obtained in this step. The amount and type of data required for analysis is dependent upon the analysis method selected. Additional site visits may be required after the initial visit to obtain supplementary data. A description of the analysis methods available for safety and operational evaluation, along with specific data requirements, are described in chapters 6 and 7. The following sections describe the data that should be collected and obtained for an office review and field investigation.
5.3.1 Office Review
Office reviews include obtaining relevant safety, operations, and design data from available resources (e.g., local public works and planning departments, State department of transportation offices, and Internet sites). As-built drawings and aerial photography should be obtained for this effort. Past studies conducted within the study area should also be obtained. In general, the office review should make use of all data that can be obtained without extraordinary expenditures.
5.3.2 Field Investigation
Field investigations should be performed to observe safety and operating conditions. Everyone involved with evaluating and recommending improvements to an intersection should visit the site. Three perspectives should be considered.
The site visit should occur during peak-hour traffic conditions. Additional field visits may be appropriate for the following conditions:
Observations of events and physical characteristics should be noted. Photographs and video should be made for reference and use in presentations and reports.
During the observation, vehicle queues and travel patterns through the intersection should be examined and noted if they interfere with upstream driveways and/or intersections. Likewise, arrival patterns, modal distribution, operations, and closely spaced downstream traffic signals should be observed to determine if they affect, or are affected by, operations at the subject intersection. Special conditions such as nearby pedestrian/bicyclist generators, transit transfer points, and populations with special needs should be noted. The type and operating characteristics of nearby commercial establishments and institutions may have an important effect on the intersection and should also be noted. The intersection’s relationship to other important system components (e.g., freeways, principal arterials, and even sensitive neighborhoods) must be recognized. To assess the system-wide impacts of a potential improvement, it is necessary to understand how the study intersection interacts with its surrounding facilities.
The following tables provide a description of the data items that should be collected as part of the office review and field investigation stages. Table 20 identifies user characteristics, table 21 identifies operational characteristics, and table 22 identifies safety characteristics. Table 23 identifies physical characteristics such as geometry, traffic signal control, and land use, and table 24 lists key policy and background information that should be obtained.
5.4 Problem Identification
Problems at an intersection are identified through a synthesis of stakeholder interviews, office reviews, field investigations, and preliminary operational and safety analysis. To determine whether a problem exists, this information needs to be evaluated against defined goals or standards. a problem statement can be defined after a review of the established operational and safety criteria against the known characteristics of an intersection. In some cases, additional data may need to be collected to confirm that a problem exists.
The steps for identifying problems as described in this chapter are: (1) establish performance measures and criteria; (2) summarize operational and safety conditions; and (3) develop a problem statement.
Table 20. User characteristics.
Table 21. Operational characteristics.
Table 22. Safety characteristics.
Table 23. Geometric, traffic signal control, and land use characteristics.
Table 24. Policy and background information.
5.4.1 Establish Performance Measures and Criteria
The selection of performance measures should be made on a case-by-case basis; the measures should address concerns raised by stakeholders and issues identified during the office review and field investigation. Table 25 lists common concerns of motorists, pedestrians, transit riders, bicyclists, and facility managers.
Table 25. Common concerns raised by stakeholders.
Ideally, performance measures are quantitative and can be measured for a future-year condition to evaluate the long-term effects of potential treatments. Certain cases, however, may require selection of qualitative performance measures, particularly when evaluating characteristics such as driver expectations and pedestrian/bicyclist comfort.
Once performance measures are defined that adequately address the scope of the issues, desired performance levels should be established for each measure. This process should take into account local policy and standards, driver expectations, operational and safety levels at similar facilities, and research findings. All decisionmakers on a project should agree on the performance levels established.
Desired levels of performance should be defined for all study periods and years. For operational evaluations, the typical weekday peak hour(s) should be included in the evaluation. Other conditions may be included as deemed necessary. Operational performance levels should be established for year of opening and long-term (20 to 25 years) conditions. For safety evaluations, performance levels are generally established on an annual basis and evaluated over a period of 3 to 5 years.
The desired performance level may vary based on time of day and year. For an operational issue, a degraded level of performance may be tolerated for certain periods of the day while more stringent standards are applied for the remaining periods. Similarly, a worsened operating condition may be tolerated better under long-term conditions than near-term conditions.
In some cases, particularly for multimodal aspects, it may be difficult to establish quantifiable performance levels. Performance levels for these cases may be based on a design element (e.g., sidewalk width, buffer, distance to transit stop). Efforts should be made to establish quantifiable levels to effectively assess the impact of various treatments.
Table 26. Example performance measures and criteria.
As shown in table 26, certain performance measures are readily quantifiable (critical movement volume-to-capacity ratio, average vehicle delay, queues), while others have a higher level of uncertainty for prediction (total intersection crashes, approach speeds) or require a qualitative assessment (multimodal impacts and way-finding). While some measures are not easily quantifiable, it is important that they be recognized and considered in the evaluation and selection of intersection treatments.
5.4.2 Summarize Operational and Safety Conditions
Problems at an intersection usually are related to a safety or operational deficiency. Defining a problem generally requires an assessment of performance from the perspective of all users of the intersection, regardless of mode of travel. At this stage in the project, a primary problem may have already been defined and be the cause for initiating the project. In these instances, the operations and safety conditions should be reviewed to confirm the problem exists and determine whether other problems exist or likely will exist in the future.
The level of effort required for determining operational and safety conditions at this stage varies from intersection to intersection. The information gathered through the stakeholder interviews and office review/field investigation may be sufficient in some cases, while other situations may require more extensive operational and safety evaluations.
Common questions that should be answered in evaluating intersection safety and operations are:
A complete description of analysis procedures that can be applied to estimate safety and operations conditions for signalized intersections and answer the above questions is provided in chapters 6 and 7.
5.4.3 Develop Problem Statement
After comparing the operational and safety conditions of an intersection against the established performance measures, problems and deficiencies should begin to emerge. Deficiencies should be expressed in terms of the user group (motorist, pedestrian, bicyclist, etc.) and reference the specific movement that initiates the problem as well as the time and duration during which the problem occurs. For example, a safety condition could be expressed as: an excessive number of rear-end collisions involve vehicles traveling on the northbound approach during wet-weather conditions. An operational problem could be stated as: an eastbound left-turn movement operates over capacity during the weekday p.m. and Saturday peak periods.
Problems should be stated in terms of the performance measures defined earlier in this chapter. Example problem statements follow.
5.5 Identify Problem Cause
Once the problems at an intersection have been identified, initiative should be taken to determine the cause of each. The previous section explained that the effect of a problem is often a deficient safety or operational performance measure. The cause of the problem, in many cases, is attributable to a design element. As an example, a safety problem with an effect of a high occurrence of sideswipe collisions on an approach with dual left-turn lanes may be caused by inadequate lane width and a lack of delineation for the left-turn lanes.
Aerial photography and as-built drawings should be used to assist in the determination of problem cause. Results from the office review, field investigation, and preliminary analysis should also be used to determine possible causes. Detailed review of all elements of a signalized intersection, as described in previous chapters, are required to determine the cause of a problem.
Table 27 provides lists possible causes related to common operational and safety deficiencies. This list should be applied to specific movements and approaches where an operational or safety deficiency may be occurring.
Table 27. Possible causes of intersection problems.
5.6 Treatment Selection
Treatments should be selected that address the specific areas for safety and operational improvement identified in the preceding stages of the intersection evaluation process. The primary objectives of the treatment selection stage are to (1) identify the range of treatments; (2) evaluate treatments; (3) assess potential for undesirable effects; and (4) determine costs and implementation issues.
5.6.1 Identify Range of Treatments
What treatments are likely to influence the areas for safety and operations improvement? The range of treatments provided in this guide are categorized into the following chapters:
A list of identified treatments is provided in chapter 1. A complete discussion of the safety, operational, and design characteristics of each treatment is provided in part III of this guide, which also discusses the applicability of each treatment and identifies the problem and cause the treatment addresses. The level of detail provided for each treatment varies based on the amount of research and field evaluation available. It should be noted that treatments listed in this guide by no means represent the full extent of treatment possibilities.
5.6.2 Evaluate treatments
Once possible treatments have been listed that could address the identified problems, it is necessary to evaluate the possible countermeasures to determine the potential for improvement to safety and operations. Treatment descriptions in part III describe the impact each treatment has on safety and operations. Where available, crash modification factors are provided to estimate the possible reduction in crashes. Operational benefits can be determined based on performing an analysis described in chapter 7.
5.6.3 Assess Potential To Introduce Undesirable Effects
In addition to considering the potential safety and operational improvements that countermeasures can offer, consideration needs to be given to the possibility that countermeasures can have negative effects. Efforts should be made to assess the likelihood of introducing undesirable safety or operational consequences through the implementation of recommended countermeasures. These undesirable effects include the potential for a treatment to result in:
5.6.4 Determine Costs and Implementation issues
Costs are usually assessed in three categories: capital costs, operating costs, and maintenance costs. Other issues that should be considered include right-of-way needs, ADA compliance, environmental impacts, constructability, and maintenance of traffic.
Capital costs are normally associated with initial construction and implementation. The installation of traffic signals, for example, involves design, materials, construction, and installation costs normally paid for out of a capital program fund. This is normally a one-time cost. Where the capital investment is projected to occur some time in the future (e.g., grade separation 10 years from now), these costs must be discounted back to present value to enable a fair comparison with other alternatives.
The final decision to implement treatments should incorporate a wide range of parameters that decisionmakers deem appropriate. While operational benefits, safety benefits, and cost are key criteria, they are not the only elements that must be considered. Other criteria, such as coordination with other projects, special funding, and ADA transition plan requirements, may dictate the implementation and timing of a project.
5.7 In-Service Assessments
5.7.1 Followup Plan
Identifying and documenting the physical and operational hazards determined during the safety assessment should be coupled with a followup plan. The plan should identify what measures will be taken by whom and when, and it should effectively communicate these decisions to each of the stakeholder groups identified above.
The objective of a followup plan is to ensure that the:
Where the action of others is required to achieve the implementation of a recommendation, an appropriate followup system should be implemented. The system should endeavor to do more than simply monitor the status of other activities. If recommendations involve the need for design, those involved in the intersection evaluation process can use the followup process to comment on design and installation details before the remedial measures and countermeasures are ultimately installed. Staff familiar with the original intent of these measures should also ensure that the proposed measure was installed as directed.
5.7.2 Monitoring program
A monitoring program should be developed to evaluate the impacts of countermeasures that are selected and implemented. The scope of the monitoring program will be a function of the nature of the countermeasures and their likely effects on operations and safety at and adjacent to the study location. Ideally, data would be collected prior to construction of a treatment to provide a benchmark for future comparisons. The objectives of the monitoring program are to:
The monitoring program should have a clearly understood monitoring frequency, duration, and objectives, as appropriate for the measure installed. The need to advise stakeholders of the monitoring program should be considered, but may not always be necessary. However, should the monitoring program result in a modification or removal of the originally proposed countermeasures, further notification to the stakeholders is required.
A key goal of the program is to be able to continually improve the road system, constantly seeking to reduce the number of collisions that occur on roads within the jurisdiction and improve the operational efficiency.
Keywords: Signalized Intersections, Intersection Safety, Intersection Design, Intersection Performance, Intersection Treatments
TRT Terms: Roads–Interchanges and intersections, Roads–Interchanges and intersections–Safety measures, Traffic signs and signals, Signalized intersections, State of the art reports, Best practices