CHAPTER 1

Introduction

Background

The level of service (LOS) concept has been used for over 50 years by state departments of transportation (DOTs) for policy setting, planning, analysis, and communication efforts. Individual adoption of the LOS framework by DOTs has generally been consistent with the Highway Capacity Manual (HCM) although usage and application may vary across different state DOTs. Some DOTs may also have tailored their respective LOS definitions and applications for local conditions, multimodal analysis, and threshold values such as adjustment of HCM’s LOS category definitions (e.g., extrapolating or delineating failure conditions). Additionally, there are differences in how DOTs use big data and modern communication tools in their LOS analyses. As a result of this widespread application of the HCM concepts, there is a need for a greater understanding of DOT practices concerning the usage, adaptations, and adoption of the HCM LOS framework.

Objectives and Scope

The objectives of this synthesis were to review and document state DOT practices concerning the usage and adaptations of the HCM LOS framework for varying levels of applications, such as policy setting, planning, operational analysis, and communication practices. The scope of the synthesis includes the following topics:

• The use of the HCM LOS framework or other adopted frameworks for various tasks related to policy, planning, design, and operations.
• The exact LOS methodologies adopted by the DOTs for each transportation facility and mode.
• Deviations and adaptations of the HCM LOS methodologies.
• Use of traffic analysis tools for LOS analysis and communication purposes.
• Data availability for LOS determination and the role of big data for determining LOS criteria.

Definitions

For this synthesis, the following definitions are used:

• DOT: A state-mandated agency from the 50 states or the District of Columbia responsible for managing and overseeing transportation-related matters.
• HCM: A guide developed by the Transportation Research Board (TRB) that provides methodologies and guidelines for assessing quality of service, capacity, and performance of various transportation facilities. For the purposes of this report, the most recent edition of the HCM is used (Transportation Research Board, 2022).

• LOS: A quantitative stratification of a performance measure or measures representing quality of service (Transportation Research Board, 2022). Conventionally, HCM-based LOS is an alphabetical grading system from LOS A (free-flow conditions) to LOS F (failure condition).
• LTS: A methodology for assessing the perceived comfort and safety of pedestrians and bicyclists.
• Probe data: Information collected from mobile devices or vehicles.
• Big data: Combination of data generated from various sources, such as mobile devices, vehicles, roadway sensors, public transportation systems, weather condition and environmental data, smart infrastructure, etc.
• Emerging technologies: Key technologies that focus on safer, more efficient, and sustainable ways to move people and goods, such as connected and automated vehicles (CAVs), electric vehicles, micromobility, mobility-as-a-service, etc.

Methodology and Outline

Information for this synthesis was obtained through three main activities: a literature review, an online survey of state DOTs, and interviews with selected state DOTs to develop specific case examples. These activities are summarized below, while the detailed results are presented in Chapters 2, 3, and 4. The synthesis conclusions are presented in Chapter 5.

Literature Review

Literature sources, including state guidance and policy documents, online websites describing DOT practices for using LOS or other performance measures for various applications were reviewed and synthesized. The reviewed documents were accessed through online searches covering topic areas related to LOS criteria, traffic performance measures, and traffic analysis processes. The summary of the literature review is presented in Chapter 2.

Survey

An online survey was distributed to the DOTs for all 50 states and the District of Columbia. The survey was built using an online platform. Responses were received from 41 out of the 51 DOTs (80%). The survey was distributed to transportation engineers working within the planning, traffic, or design offices (e.g., traffic operations engineers, mobility managers, planning managers, etc.) because the HCM LOS framework has many different uses and applications. The list of contacts was compiled after consultation with FHWA, TRB, and information collected from the state DOTs’ websites. The survey instructions encouraged the transportation engineers to share the survey with others within their DOT who could potentially respond more accurately to some of the questions and report the gathered responses. The survey included a total of 20 questions, the first two questions of which asked about their contact information and respective state DOT. The third question of the survey asked if the state DOT is using LOS concepts. Respondents who indicated their DOT is not using any LOS concepts were asked one follow-up question regarding alternative performance measures used for various applications. Respondents who indicated their DOT uses LOS concepts were asked 17 follow-up questions. All responding DOTs indicated they use LOS concepts. Appendix A presents the online survey questionnaire and Chapter 3 summarizes the survey results. The individual survey responses are presented in Appendix B.

Case Examples

The survey responses were reviewed to identify state DOTs with variable usage and adaptations of the HCM LOS framework. The last question of the survey asked about state DOTs’ willingness to participate in the follow-up interviews to discuss the case examples. A total of 17 DOTs showed

interest in participating in the interviews. The selection of the DOTs considered the variability in the use of the HCM LOS framework, geographic diversity of the state location, area type, population size, weather/climate conditions, and willingness to participate in follow-up interviews. Based on the selection criteria, six case example DOTs were identified: Arkansas DOT, Minnesota DOT, Washington State DOT, Arizona DOT, New York State DOT, and North Carolina DOT. Virtual 1-hour interviews were conducted with DOT personnel to discuss their use of LOS concepts and develop case examples. In the cases of Washington and New York, more than one person attended the online interviews. Chapter 4 includes the results of each DOT case example and a summary of the experience gained. The list of the questions and prompts used during the online interviews is provided in Appendix C.