NCHRP Web-Only Document 460

Designing for Target Speed

Volume 1: Operating Speed and Road Elements

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COOPERATIVE RESEARCH PROGRAMS

CRP STAFF FOR NCHRP WEB-ONLY DOCUMENT 460, Volume 1

Monique R. Evans, Director, Cooperative Research Programs

Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program

Camille Crichton-Sumners, Senior Program Officer

Dajaih Bias-Johnson, Senior Program Assistant

Natalie Barnes, Director of Publications

Brian Haefs, Associate Director of Publications

Jennifer J. Weeks, Publishing Projects Manager

NCHRP PROJECT 15-76(01) PANEL
Field of Design—Area of General Design

Christine A. Spangler, Pennsylvania Department of Transportation, Harrisburg, PA (Chair)

Rachel A. Carpenter, California Department of Transportation, Sacramento, CA

Jody J. Colvin, Louisiana Department of Transportation and Development, Baton Rouge, LA

Eric E. Marabello, Maryland Department of Transportation, Baltimore, MD

John M. Mason, Jr., Kittelson & Associates, Inc., Pooler, GA

Hugh W. McGee, Sr., Springfield, VA

Khang M. Nguyen, Houston Public Works, Houston, TX

Samuel Offei-Addo, BSC Group, Inc., Boston, MA

Gustavo Riente de Andrade, Infraplan Consultoria Ltda, Gainesville, FL

Robert Mooney, FHWA Liaison

Clayton Wellman, FHWA Liaison

Patricia Bush, AASHTO Liaison

AUTHOR ACKNOWLEDGMENTS

The research reported herein was performed under NCHRP Project 15-76 and NCHRP Project 15-76(01) by the Texas A&M Transportation Institute (TTI), a member of The Texas A&M University System.

Marcus Brewer, TTI research engineer, was the principal investigator and Kay Fitzpatrick, TTI research fellow, was the co-principal investigator. The authors of this report are:

• Marcus Brewer (TTI).
• Kay Fitzpatrick (TTI).
• Eun Sug Park (TTI).
• Boniphace Kutela (TTI).

The work was performed under the general supervision of Mr. Brewer. The research reported here was supported by multiple staff members at TTI (Emma Turner, Stacey Alejandro, Melanie Guerra, Subarna Pokhrel, David Schrank, Lauren Geng, Michael Martin, Gary Barricklow, Steven Venglar, Minh Le, Kaloyan Debiyski, Caden Reed, Cole Pearson, Ashlee Wallace, Brandon Sullivan, Nicolas Covarrubias, and Sammy Rangel). The authors also recognize the contributions of Subasish Das and Maryam Mousavi, former TTI staff members, who contributed to the early tasks of the project.

The authors acknowledge the contributions of our research team partners at Kimley Horn (Mark Lenters, Lindsay Saner, John Karachepone, and Kathy Falk), who provided insights on the research from the practitioner perspective, to facilitate the implementation of the research in the profession. The authors also wish to acknowledge the additional practitioner colleagues who either shared information or participated in discussions on current practices, potential study locations, and possible evaluation topics. The authors appreciate the time and effort of these individuals.

CONTENTS

Summary

Chapter 1. Background

Objective and Scope

Purpose and Organization of Final Report

Chapter 2. Research Approach

Research Questions

Research Methodology for NCHRP Project 15-76

Phase I Efforts

Phase II Efforts

Chapter 3. Findings and Applications

Literature Review

Current Practices

Data Framework and Sources

Analytical Approach

Suitability of INRIX XD Speed Data

Data Collection and Analysis

Practitioner’s Guide

Technology Transfer

Documentation of Research Efforts

Chapter 4. Conclusions, Recommendations, and Suggested Research

Conclusions From Review of Literature and Current Practices

Conclusions From Investigation of Relationships Between Operating Speed and Road Elements

Conclusions From Practitioner’s Guide

Recommendations

Suggested Research

Appendix A. Review of Literature on Speed Concepts and the Design Process

Speed Concepts

Target Speed

Other Speed Terms

Design Speed

Operating Speed

Posted Speed Limit

Use of Speed in the Design Process

Planning

Roadway Design

Traffic Engineering

Factors that Affect Operating Speed

Overview

Multiple Roadway Environments

Lower-Speed or Urban Environments

Appendix B. Review of Current Practices

ITE Recommended Practice Designing Walkable Urban Thoroughfares: A Context Sensitive Approach

FHWA Speed Limit Setting Handbook

Florida DOT

Washington State DOT

Oregon DOT

Massachusetts DOT

Texas DOT

City of Austin

City of Charlotte

City of Chicago

Appendix C. Proposed Data Framework for Investigating the Relationship of Speed with Road Elements

Overview of Conceptual Framework for Database

Recommendation for the Proposed NCHRP 15-76 Database

Potential Sources for Study Sites

NCHRP 17-76

TxDOT 0-7049

FHWA, Development of Pedestrian-Intersection Crash Modification Factors Project

NCHRP 3-141

City of Portland

City of Dallas

States of Maine, Massachusetts, Ohio, Utah, Virginia, and West Virginia

Cities of Tucson, Minneapolis, and Detroit

Potential Sources of Location Data

Potential Sources of Speed Data

INRIX XD™

Overview

Sample Dataset – Texas

National Performance Management Research Data Set

Overview

Sample Dataset – Austin, Texas

StreetLight

Wejo

Traditional Data Collection Methods

Existing Data (Binned Speed Data)

Potential Sources of Traffic Data

Potential Sources of Census Data

Summary

Appendix D. Development of Analytical Approach

Developing Preliminary Models for Operating Speed Analysis

Phase I Evaluation of Preliminary Models and Data for Speed Analysis

Model 1

Model 2

Model 3

Model 4

Model 5

Model 6

Model 7

Summary of Findings for Preliminary Models

Selected Factors for Phase II Target Speed Analysis

Study Site Selection Process for Phase II Target Speed Analysis

Appendix E. Suitability of INRIX XD™ Speed Data

Speed Data

Spot Speed Data Measured at the Site

Speed Data Measured Using Probe Vehicles

Sites with Both Speed Measured at the Site and INRIX XD Speed

Site Characteristic Database

Speed Measures

Speed Measures from Previous Study

Speed Measures using Data Collected at a Spot Location

Speed Measures using Data Collected along a Segment

Speed Measures for this Study

Developing Models for Operating Speed Anaysis

Comparison of Findings for Different Speed Measures Based on Sites with Tube Speeds

Comparison of Findings for Different Speed Measures Based on Sites with Speeds Based on Free-Flow Vehicles

Recommendation for NCHRP 15-76 Phase II Analyses

Appendix F. Relationships Between Operating Speed and Road Elements on Roads with 25 to 40 mph Speed Limits

Data Collection / Building Database

Segment Identification

INRIX Speed Data

Sources for Segment Characteristics

Roadway Characteristics Data

Round 1

Round 2

Round 3

Round 4

Round 5

Round 6

Review of Variables Collected Using Google Earth Images

EPA Smart Location Database (SLD)

U.S. Buildings Footprint

Building Height

Schools

Traffic Volume and Posted Speed Limit

Assembled Database for Analysis

Analysis

Variables and Summary Statistics

Analysis Approach

Findings

Posted Speed Limit Evaluation

Transportation Professional Evaluation

Demographics and Transportation Professional Evaluation

Discussion

Limitations

Appendix G. Supplemental Investigation of Average Lane Width, Center Line Markings, and Edge Line Markings

Introduction

Average Lane Width

When Should Center Line and Edge Line Markings Be Used

Development of Subsets

Model Results

Analysis and Findings

Lane Width (AvgLaneWidth)

Center Line (CenterTreat_1yes) and Edge Line (Elmark_DirOfTravel) Markings

Discussion

Appendix H. Suggested Modifications to Standard References

AASHTO Green Book

TRB Highway Capacity Manual (HCM)

FHWA Manual on Uniform Traffic Control Devices (MUTCD)

ITE Designing Walkable Urban Thoroughfares: A Context Sensitive Approach

ITE Implementing Context Sensitive Design on Multimodal Corridors: A Practitioner’s Handbook

Appendix I. References

LIST OF FIGURES

Figure 1. Example of urban street with 30-mph posted speed limit

Figure 2. Example of residential street with 30-mph posted speed limit

Figure 3. Example of street with 35-mph posted speed limits with shoulders

Figure 4. Example of street with 35-mph posted speed limits with urban elements such as curb and bus stop

Figure 5. Example of street with 35-mph posted speed limits with sidewalks attached to curb

Figure 6. Example of street with 35-mph posted speed limits with buffer-separated sidewalks

Figure C-1. Example of roadway, roadside, and non-roadway element zones

Figure C-2. NCHRP 15-76 database format and flow chart

Figure D-1. Close-up view of MPS-464 site

Figure D-2. Example of 5 segments (10 readings, 2 readings per segment) near MPS-464 site

Figure F-1. Number of access points for undivided roadways

Figure F-2. Number of access points for divided roadways

Figure F-3. Example of 5-ft and 50-ft buffers around an INRIX XD segment to identify whether a building is within the given buffer

Figure F-4. An example of a school within a 0.5-mile buffer of the INRIX XD segment

Figure G-1. Average lane width (number of segments) versus ffspd and cumulative distribution for full database

LIST OF TABLES

Table A-1. Definitions of selected speed terms

Table A-2. Factors that could influence setting or achieving target speed

Table B-1. Speed management strategies from 2020 Florida DOT Design Manual. (adapted from Table 202.3.1 in Florida DOT 2020b)

Table B-2. Transportation characteristics that support target speeds from Florida DOT. (adapted from Table 8 in Florida DOT 2020a)

Table B-3. Target speed based on land use context and roadway type from Washington State DOT. (adapted from Exhibit 1103-4 in Washington State DOT 2021)

Table B-4. Recommended Oregon DOT target speed and design treatments for urban contexts. (Oregon DOT 2020a, Oregon DOT 2020b)

Table B-5. Recommended MassDOT process, documentation, and reviews for identifying target and design speed. (Table 3-6 in Massachusetts DOT 2023)

Table B-6. Recommended MassDOT target and design speed ranges by area type and roadway type. (Table 3-7 in Massachusetts DOT 2023)

Table B-7. Multimodal design table from Austin, Texas. (adapted from Austin Transportation Department 2017)

Table B-8. Street types and associated characteristics from Charlotte, North Carolina. (adapted from Charlotte DOT 2007)

Table B-9. Design elements for street types in Chicago, Illinois. (adapted from Chicago DOT 2013)

Table C-1. Factors within the location subcategories to be considered

Table C-2. Summary of sources for speed data

Table C-3. INRIX XD™ data file format

Table C-4. Summary of segments chosen to review INRIX XD™ data

Table C-5. TMC time file format in NPMRDS. (Schuman et al. 2021)

Table C-6. Potential amount of NPMRDS speed data for Lamar Boulevard in Austin, Texas

Table C-7. Percentage of yearly epoch coverages by TMCs

Table C-8. Census-related factors to be considered

Table D-1. Description of variables used in the preliminary analysis

Table D-2. Summary statistics for variables used in the Phase I analysis

Table D-3. Model 1 summary of fit

Table D-4. Model 1 analysis of variance

Table D-5. Model 1 parameter estimates

Table D-6. Model 1 effect tests

Table D-7. Model 2 summary of fit

Table D-8. Model 2 analysis of variance

Table D-9. Model 2 parameter estimates

Table D-10. Model 2 effect tests

Table D-11. Model 3 summary of fit

Table D-12. Model 3 analysis of variance

Table D-13. Model 3 parameter estimates

Table D-14. Model 3 effect tests

Table D-15. Model 4 summary of fit

Table D-16. Model 4 analysis of variance

Table D-17. Model 4 parameter estimates

Table D-18. Model 4 effect tests

Table D-19. Model 5 summary of fit

Table D-20. Model 5 analysis of variance

Table D-21. Model 5 parameter estimates

Table D-22. Model 5 effect tests

Table D-23. Model 6 summary of fit

Table D-24. Model 6 analysis of variance

Table D-25. Model 6 parameter estimates

Table D-26. Model 6 effect tests

Table D-27. Model 7 summary of fit

Table D-28. Model 7 analysis of variance

Table D-29. Model 7 parameter estimates

Table D-30. Model 7 effect tests

Table D-31. Selected predictors for SpdAve in each of Model 1-Model 7

Table D-32. Description of factors chosen for Phase II

Table D-33. Number of sites with INRIX XD™ speed data

Table D-34. Summary of potential sources for Phase II study sites

Table D-35. Summary of study sites contained in available databases

Table E-1. Number of sites by number of roadway lanes, posted speed limit, and source of the on-road collected speed data

Table E-2. Description of variables collected by research team

Table E-3. Description of variables from Smart Location Database

Table E-4. Summary statistics for variables initially considered for the analysis for the 128 sites where spot speeds were collected using road tubes

Table E-5. Summary statistics for variables initially considered for the analysis for the free-flow data (based on 21 sites)

Table E-6. NCHRP 17-76 Round 2 speed measures considered

Table E-7. Summary statistics for speed measures considered for the analysis (128 tube data sites)

Table E-8. Multivariate correlations for speed measures

Table E-9. Summary statistics for speed measures considered for the analysis (21 free-flow data sites)

Table E-10. Variable selection methods

Table E-11. Comparison of variables selected for different speed measures when considering all seven selection methods for 128 sites with speeds measured with tubes

Table E-12. Comparison of variables selected for different speed measures when considering the AICc-based two selection methods for 128 sites with tube-measured speeds

Table E-13. Comparison of variables selected for different speed measures when considering the BIC-based selection methods for 128 sites with tube-measured speeds

Table E-14. Comparison of variables selected for different speed measures when considering all seven selection methods for the 21 sites where free-flow speeds are available

Table F-1. Description of variables used in the analysis that were collected by research team in Round 1 and refined in later rounds

Table F-2. Description of variables used in the analysis that were collected in Round 2 and Round 6

Table F-3. Description of variables used in the analysis that were collected by research team using measurements from aerial photographs in Round 3

Table F-4. Description of variables used in the analysis that were collected by research team in Round 4 and Round 5

Table F-5. SLD variable description

Table F-6. Description of SLD variables that were used in the final analysis

Table F-7. Distribution of C_BuildingSetback by state

Table F-8. Distribution of C_BuildingSetback by PSL

Table F-9. Building height categories and associated descriptions (Falcome 2016)

Table F-10. A sample of joined building height data for a selected INRIX XD segment

Table F-11. A sample of final building height database

Table F-12. Distribution of C_BuildingHeight by state

Table F-13. Distribution of C_BuildingHeight by PSL

Table F-14. Data sources for schools

Table F-15. Data sources for traffic volumes and posted speed limits

Table F-16. Number of segments by state and posted speed limit

Table F-17. Variable descriptions

Table F-18. Summary statistics for variables used in the analysis (N=6327)

Table F-19. Summary of fit for analysis using posted speed limit variable only

Table F-20. Parameter estimates for analysis using posted speed limit variable only (N=6327)

Table F-21. Parameter estimates for analysis using variables that could be influenced by a transportation professional (N=6327)

Table F-22. Type 3 test of fixed effects results for analysis using variables that could be influenced by a transportation professional (N=6327)

Table F-23. Parameter estimates for analysis using all variables in the model with demographics variables (N=6327)

Table F-24. Type 3 test of fixed effects results for analysis using all variables in the model with demographics variables (N=6327)

Table G-1. Key characteristics of subsets

Table G-2. Parameter estimates for analysis using the 3838 subset

Table G-3. Type 3 test of fixed effects results for analysis using the 3838 subset

Table G-4. Parameter estimates for analysis using the 2232 subset

Table G-5. Type 3 test of fixed effects results for analysis using the 2232 subset

Table G-6. Summary statistics for the 2232 subset

Table G-7. Parameter estimates for analysis using the 1606 subset

Table G-8. Type 3 test of fixed effects results for analysis using the 1606 subset

Table G-9. Summary statistics for the 1606 subset

Table G-10. Parameter estimates for analysis using the 1598 subset

Table G-11. Type 3 test of fixed effects results for analysis using the 1598 subset

Table G-12. Summary statistics for the 1598 subset

Table G-13. Parameter estimates for analysis using the 979 subset

Table G-14. Type 3 test of fixed effects results for analysis using the 979 subset

Table G-15. Summary statistics for the 979 subset

Table G-16. Parameter estimates for analysis using the 526 subset

Table G-17. Type 3 test of fixed effects results for analysis using the 526 subset

Table G-18. Summary statistics for the 526 subset

Table G-19. Parameter estimates for analysis using the 295 subset

Table G-20. Type 3 test of fixed effects results for analysis using the 295 subset

Table G-21. Summary statistics for the 295 subset

Table G-22. Parameter estimates for analysis using the 72 subset

Table G-23. Type 3 test of fixed effects results for analysis using the 72 subset

Table G-24. Summary statistics for the 72 subset

Table G-25. Parameter estimates for analysis using the 66 subset

Table G-26. Type 3 test of fixed effects results for analysis using the 66 subset

Table G-27. Summary statistics for the 66 subset

Table G-28. Estimates for AvgLaneWidth Variable for the subsets

Table G-29. Number of segments and ADT range by presence of center line markings

Table G-30. Number of segments and AADT range by presence of edge line markings

Table G-31. Number of segments and edge-to-edge width range by presence of center line markings

Table G-32. Estimates for CenterTreat_1yes variable for select subsets

Table G-33. Estimates for Elmark_DirOfTravel variable for select subsets