# Presentation: 541291

## Speed Management and Engineering Related Issues

- John M. Mason, Jr.
*The Pennsylvania State University*
- National Forum on Speeding
- Washington, DC
- June 15 – 16, 2005

## Presentation Content (per invitation)

- Speed Management Concept
- TRB Special Report 254 Managing Speed
- Engineering Aspects
- Design Speed
- Operating Speed
- Speed Limit

## Acknowledgements

- TRB Special Report 254: Managing Speed (1998) “Review of Current Practice for Setting and Engineering Speed Limits”
- “Conceptual Approach to Relate Design Speed, Operating Speed, and Posted Speed Limits” with Kevin Mahoney and Eric T. Donnell, Pennsylvania Transportation Institute, Penn State University
- NCHRP Project 15-25, “Alternatives to Design Speed for Selection of Roadway Design Criteria.” MRI and PTI. (D. Harwood, D. Torbic, K. Mahoney, R.J. Porter, J.M. Mason)

## Slide 4

## Committee for Guidance on Setting and Enforcing Speed Limits

- John G. Milliken, Chairman, Venable, Baetjer & Howard, McLean, Virginia
- Forrest M. Council, University of North Carolina, Chapel Hill
- Terrance W. Gainer, Metropolitan Police Department, 	Washington, DC
- Nicholas J. Garber, University of Virginia, Charlottesville
- Kristine M. Gebbie, Columbia University School of Nursing, New York
- Jerome W. Hall, University of New Mexico, Albuquerque
- Charles A. Lave, University of California, Irvine
- John M. Mason, Jr., The Pennsylvania State University, University Park
- Frederick Mosteller, Harvard University, Cambridge

## Committee for Guidance on Setting and Enforcing Speed Limits (con’t)

- Sharon D. Nichols, Western Highway Institute, Casper, Wyoming
- Clinton V. Oster, Jr., Indiana University, Bloomington
- Richard A. Retting, Insurance Institute for Highway Safety, Arlington, 	Virginia
- Thomas B. Sheridan, Massachusetts Institute of Technology, Cambridge
- William C. Taylor, Michigan State University, East Lansing
- George Tsebelis, University of California, Los Angeles
- David C. Viano, General Motors Corporation, Warren, 	Michigan
- Richard P. Weaver, California Department of Transportation (retired), 	Sacramento

## Liaison Representatives

- Stephen F. Campbell, Sr., American Trucking Associations, Alexandria, Virginia
- Richard P. Compton, National Highway Traffic Safety Administration, Washington, DC
- Mark Edwards, American Automobile Association, Heathrow, Florida
- David J. Hensing, American Association of State Highway and Transportation Officials, Washington, DC
- Henry Jasny, Advocates for Highway and Auto Safety, Washington, DC
- Richard Pain, Transportation Research Board, Washington, DC

**Transportation Research Board Staff**

-    Nancy P. Humphrey, Study Director

## Scope

- State of knowledge and practice re:
-  Setting speed limits
-  Speed : Safety
-  Road design : Speed limits
- New and emerging technologies for speed management and enforcement
- Guidance regarding current practices

## Guidance

- Relevant studies and data did not provide sufficient support for quantifying the efforts of change in speed limits on driving speeds and safety.
- It was found that current practice of setting speed limits is a reasonable balance between speeds and risks under favorable operating conditions.
- Periodic review of driving speeds and crash experience to monitor changes over time.
- Speed limits in speed zones should be based on an engineering study.

## Other speed management strategies

- Roadway Design and Traffic Control
- Designing Roads to Manage Speed
- Traffic Calming
- Traffic Control Devices
- Perpetual countermeasures (reduced lane width, pavement surface roughness, markings, chevrons, delineation...)
- Vehicle and Highway Technologies
- In vehicle displays and controls
- Variable message / variable speeds
- Automated Vehicle / Highway System

## Design Speed – Background Definitions

- AASHO (1940) ... “maximum approximately uniform speed ... by faster group of drivers.”
- AASHTO (1954 – 1994) ... “maximum safe speed ... favorable conditions ... design features govern.”
- AASHTO (2001 – 2004) ... “a select speed used to determine the various geometric design features of a roadway.”

## Design Speed            Operating Speed

- ...while an anticipated operating
- 	speed is often a consideration in
- 	design, operating speeds are
- 	typically not predicted during design...

## Design Process Flow 

## Stopping sight distance		++
Horizontal curve radius		+++
Vertical grades				+++
Lane widths				+
Clear zone				+++
Median type				+++
Access density				+++

- Horizontal curve radius		+++
- Vertical grades				+++
- Lane widths				+
- Clear zone				+++
- Median type				+++
- Access density				+++

- Design elements with direct AASHTO design speed relationship:

## Relationship between Design and Operating Speed 

- Relationship between Design and Operating Speed** **

## Speed Relationships 

## Operating Speeds > Design speeds
Design speeds ≠ Speed Limits
Above minimum values increases operating speeds
Design speed : safety relationship unknown
Continued increase for design flexibility
“Maximum safe speed” 	    Tort issues

- Design speeds ≠ Speed Limits
- Above minimum values increases operating speeds
- Design speed : safety relationship unknown
- Continued increase for design flexibility
- “Maximum safe speed” 	    Tort issues

- Selection of design speeds not directly related to operating speeds create dilemmas:

## Design Speed Concepts Experience:

- “de facto” acceptance
- “set it” then “use it”
- Subjective (flexible?)
- Conservative (safe?)
- Inconsistency with operating and ported limits
- Inconsistent alignment / geometric features
- Tort liability implications / claims

## Operating Speed Models (examples)

- Leisch & Leisch – Development of speed-profiles
- Lamm – degree of curve, tangents, 85th percentile
- Krammes – Lamm + length of curve and deflection angle
- Collins & Krammes – speed reduction, tangents and curves
- Tarris, Poe, Mason – low speed urban area: curvature, grade, hazard rating, intersections and driveway and lane width
- Polus – tangent sections
- Fitzpatrick et al. – TWOPAS and speed – profile models

## Proposed Framework to Improve Design Speed Concept 

- Compare Subsequent Designs based on Functional Class, Intended Operating Speed, and Geometric Elements

- Proposed Framework to Improve Design Speed Concept** **

## Summary

- ...it is not customary U.S. practice to predict operating speeds as part of the highway geometric design process...