Safety Implications of Managed Lane Cross Sectional Elements

Printable Version [PDF, 900 KB]
You may need the Adobe® Reader® to view the PDFs on this page.
Contact Information: Operations Feedback at OperationsFeedback@dot.gov

Publication No. FHWA-HOP-16-076
December 2016

U.S. Department of Transportation
Federal Highway Administration
Office of Operations (HOP)
1200 New Jersey Avenue, SE
Washington, DC 20590

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration provides high quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No. FHWA-HOP-16-076		2. Government Accession No.	3. Recipient's Catalog No.
4. Title and Subtitle Safety Implications of Managed Lane Cross Sectional Elements			5. Report Date December 2016
			6. Performing Organization Code
7. Author(s) Kay Fitzpatrick and Raul Avelar (Texas A&M Transportation Institute)			8. Performing Organization Report No.
9. Performing Organization Name and Address Battelle 505 King Avenue Columbus, OH 43201 Texas A&M Transportation Institute State Headquarters Research Building 2935 Research Parkway Texas A&M University Research Park 3135 TAMU College Station, TX 77843-3135			10. Work Unit No. (TRAIS)
			11. Contract or Grant No. Contract No. DTFH61-12-D-00046; Task Order No. T-5012
12. Sponsoring Agency Name and Address U.S. Department of Transportation Federal Highway Administration Office of Operations 1200 New Jersey Avenue, SE Washington, D.C. 20590			13. Type of Report and Period Covered Technical Report May 2016-December 2016
			14. Sponsoring Agency Code FHWA-HOP
15. Supplementary Notes Greg Jones, FHWA Task Manager
16. Abstract The objective of this project was to investigate the relationship between crashes and buffer-separated manage lane dimensions. The results from several previous research studies have demonstrated that reductions in freeway lane width or shoulder width are associated with more crashes. A wider managed lane envelope widths (i.e., left shoulder, managed lane, and buffer width combined) are also associated with fewer freeway crashes for both all severity levels and fatal and injury severity levels. Wider envelopes are associated a reduction of 2.8 percent (in Texas) or 2.0 percent (in California) in total freeway crashes (all severities) for each additional foot of envelope width. In California, wider envelopes are associated with a reduction of 4.4 percent in managed lane-related crashes (fatal and injury severity levels) for each additional foot of envelope width. The analysis was conducted on non-weaving managed lane segments that included a single managed lane separated from the general purpose lanes with a flush buffer area. The dataset included crashes on 128.0 miles in California (all 128.0 miles with flush buffers) and 60.4 miles in Texas (41.7 miles with pylon buffers and 18.7 miles with flush buffers). The California sites included freeways with three or four general-purpose lanes while the Texas freeways had three to five general-purpose lanes.
17. Key Words Managed lane, safety, crashes, cross-section, buffer width, shoulder width		18. Distribution Statement No restrictions.
19. Security Classif. (of this report) Unclassified	20. Security Classif. (of this page) Unclassified	21. No. of Pages 52	22. Price

TABLE OF CONTENTS

• NOTICE
• QUALITY ASSURANCE STATEMENT
• LIST OF TABLES
• LIST OF FIGURES
• LIST OF ABBREVIATIONS
• CHAPTER 1: INTRODUCTION
  • Background
  • Study Objective
  • Study Approach
  • Report Organization
• CHAPTER 2: LITERATURE REVIEW
  • Managed Lanes
    • Crashes within the Managed Lane Facility
    • Crashes at Access Points
    • Safety of Buffer-Separated High Occupancy Vehicle Lanes
    • Differences in Crashes between Given Conditions
  • Freeways
  • Freeway General-purpose Lane Cross Section
  • Freeways With High Occupancy Vehicle Or High Occupancy Toll Lanes
• CHAPTER 3: SITE SELECTION
  • Selection of States
    • Highway Safety Information System Crash Data
    • Texas Data
  • Selection of Sites
• CHAPTER 4: DATA COLLECTION
  • Defining Segments
  • Variables
  • Dataset Characteristics – Geometrics
  • Dataset Characteristics – Crashes
    • Texas Crash Data
    • California Crash Data
• CHAPTER 5: ANALYSIS
  • Statistical Model / Methodology
  • Overview Of Variables Considered
  • Models on Freeway Crashes – California
    • All Severity Levels Crashes
    • All Severity Levels Crashes – Proportion of Crashes
    • Fatal and Injury Crashes
  • Models on Managed-Lane Related Crashes – California
    • All Severity Levels Crashes
    • Fatal and Injury Crashes
  • Models on Freeway Crashes – Texas
    • All Severity Levels Crashes
  • A Closer Look At Buffer Widths
• CHAPTER 6: SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS FOR FUTURE RESEARCH
  • Summary
  • Conclusions
  • Recommendations for Future Research
    • Benefits of Pylons
    • Safety Tradeoffs when Adding a Managed Lane to an Existing Freeway
    • Safety Differences between Managed Lanes with One Lane and with More than One Lane
    • Safety / Operations Differences Considering Congestion Levels
• CHAPTER 7: REFERENCES

LIST OF TABLES

• Table 1. Safety of lane width (fatal and serious injury crashes). ⁽¹⁸⁾
• Table 2. Safety change per additional lane (fatal and serious injury crashes). ⁽¹⁸⁾
• Table 3. California, number of crashes by location type for several counties.
• Table 4. Description of candidate variables.
• Table 5. Range of managed lane envelope geometric data by corridor.
• Table 6. Texas, number of crashes.
• Table 7. California, number of crashes.
• Table 8. California, preliminary model for total freeway crashes (all severities).
• Table 9. California, refined model for total freeway crashes (all severities).
• Table 10. California, preliminary model of proportion of managed lane or buffer crashes to total freeway crashes (all severities).
• Table 11. California, refined model of proportion of managed lane to total freeway crashes (all severities).
• Table 12. California, preliminary model for total freeway crashes (fatal and injury severity levels).
• Table 13. California, proportion of managed lane to total freeway crashes (fatal and injury severity levels).
• Table 14. California, refined model for managed-lane related crashes (all severity levels).
• Table 15. California, initial model for managed-lane related crashes (fatal and injury severity levels).
• Table 16. California, refinded model for managed-lane related crashes (fatal and injury severity levels).
• Table 17. Texas, initial model for total freeway crashes (all severity levels).
• Table 18. Texas, refined model for total freeway crashes (all severity levels).

LIST OF FIGURES

• Figure 1. Graphic. Buffer-separated high occupancy vehicle lanes: (a) desirable cross section with enforcement shoulders, (b) desirable cross section, and (c) absolute minimum cross section that should be used only on short-distance interim projects or short sections, e.g., across narrow bridge.
• Figure 2. Chart. Proposed crash modification factor for lane width. ⁽¹⁷⁾
• Figure 3. Chart. Proposed crash modification factor for inside shoulder width. ⁽¹⁷⁾
• Figure 4. Chart. Variation of fatal and serious injury crashes with annual average daily traffic for 10-lane freeways with high occupancy vehicle lanes from Florida study. ⁽¹⁹⁾
• Figure 5. Chart. Variation of all crashes with annual average daily traffic for 10-lane freeways with high occupancy vehicle lanes from Florida study. ⁽¹⁹⁾
• Figure 6. Graphic. Example of wide buffers on California I-405.
• Figure 7. Graphic. Example of wide buffer in California.
• Figure 8. Graphic. Another example of wide buffer, note motorcycle using the buffer area.
• Figure 9. Graphic. Example of pylons in buffer on Texas freeway.
• Figure 10. Equation. Probability distribution.
• Figure 11. Equation. Initial equation.
• Figure 12. Equation. Equation with crashes per mile-year for ith site.
• Figure 13. Equation. Equation with model random effect distribution.
• Figure 14. Chart. California, managed lane and buffer crashes by buffer width.
• Figure 15. Chart. California, freeway crashes by buffer width.
• Figure 16. Chart. Texas, freeway crashes by buffer width and presence of pylons (triangles for flush buffers without pylons and dashes for buffers with pylons).

LIST OF ABBREVIATIONS

AADT

Annual average daily traffic

AADTHV

Annual average daily traffic for the managed lane

AADTMainL

Annual average daily traffic for the general-purpose lanes

AASHTO

American Association of State Highway and Transportation Officials

Avg

Average

Buf_Type

Analysis variable; buffer type between managed lane and general-purpose freeway lanes – either pylons or flush

Buf_W

Analysis variable; buffer width

Dir

Direction

DOT

Department of transportation

EB

Eastbound

F

Flush buffer

FHWA

Federal Highway Administration

ft

Foot or feet

GP_Adj_W

Analysis variable; general-purpose lanes, width of lane adjacent to the managed lane

GP_All_Ln_W

Analysis variable; general-purpose lanes, width of all general-purpose lanes

GP_Avg_Ln_W

Analysis variable; general-purpose lanes, average lane width

GP_Ent

Analysis variable; general-purpose lanes, number of entrance ramps within the segment

GP_Exit

Analysis variable; general-purpose lanes, number of exit ramps within the segment

GP_NumLn

Analysis variable; general-purpose lanes, number of general-purpose lanes that are not barrier separated and are moving in same direction

GP_R_Shld_W

Analysis variable; general-purpose lanes, right shoulder width

GP_Trvl_W

Analysis variable; general-purpose lanes, travel width for general-purpose lanes, determined as number of lanes multiplied by average lane width

GP_Weave

Analysis variable; general-purpose lanes, number of weaving areas within the segment

HOT

High-occupancy toll

HOV

High-occupancy vehicle

HSIS

Highway Safety Information System

HV

Abbreviation used for HOV or managed lanes in analysis

Hwy

Highway

m

Meter

Max

Maximum

mi

Mile

Min

Minimum

ML

Managed lane

MLB

Managed lane or buffer related crashes

ML_L_Shld_W

Analysis variable; managed lane, left shoulder width

ML_Ln_W

Analysis variable; managed lane, lane width

ML_Env

Analysis variable; managed lane envelope which is the sum of left shoulder width, lane width, and buffer width

MRI

Midwest Research Institute

MUL

Managed use lane

NB

Northbound

NCHRP

National Cooperative Highway Research Program

NW Length

Sum of the lengths for non-weaving segments within the corridor

OLCR

Optimal lane changing region

P

Pylons present within buffer area

PSL

Posted speed limit

SB

Southbound

T_Trvl_W

Analysis variable; total travel width

veh

Vehicle

WB

Westbound

yr

Year