Flexibilities in VDOT’s Design Policies and Standards

2012

Outline

• VDOT’s Flexible Design Philosophy • Why Use Flexible Design

• Understanding what “flexibility in design” means, and why it is important

• Reveal how design flexibility is

incorporated in Green Book contents• The Value of Design Exceptions

• Risk Management and Safety• Tort Liability

• Real Life Scenario

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Why Flexible Design?

• Facilitates program/project delivery and achieving performance goals

• Allows consideration of a wider range of design options and alternatives to fit conditions

• Enables more cost-effective designs• Promotes “common sense”

engineering • Recognize and design for context

sensitive issues • Minimize project impacts• Focus on project purpose and need

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Flexible Design Philosophy

• Recognizes that flexibility is a necessary and desired aspect of the design process

• Uses a risk assessment and risk management approach for all aspects of the design

• Apply performance criteria to evaluate flexible design decisions, as well as condition criteria

• Understand the risks and consequences for design decisions – this often requires more information and higher level analysis than simply applying criteria “by the book”

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AASHTO/VDOT Flexibilities inDesign Policies and Standards

• VDOT incorporates a great deal of the flexibilities offered by AASHTO into our current project development process.

• Our current policies allow an engineer a number of choices and alternative design “tools” to allow for maximum flexibility.

• Designers have choices in design controls that effect the outcome of their project.

• Such choices allow for creative thinking, innovation in possible solutions, the ability to engage stakeholders early and fully study all design options.

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VDOT IIM 235 (CSS)

• Emphasize VDOT’s commitment to providing flexibility and innovation to our transportation challenges.

• Pave-in-Place - allows non-hard roads with traffic between 50 to 750 vpd upon approval by BOS, to be paved in place.

• Rural Rustic – Low density developments with an ADT no more than 1500 vpd

• 3R

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Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT ≤ 400)

• Addresses the unique design issues of determining appropriate cost-effective geometric design policies for very low-volume local roads

• Covers both new and existing construction projects.

• May be used in lieu of the Green Book for those facilities.

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Green Book Encourages 3R Designation Where Appropriate

“Specific site investigations and crash history analysis often indicate that the existing design features are performing in a satisfactory manner. The cost of full reconstruction for these facilities, particularly where major realignment is needed, will often not be justified.”

Green Book Forward

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3R Design Guidance

• TRB Special Report 214 is a commonly used reference for 3R criteria

• A “safety conscious” approach for improvement of safety performance

• Evaluation of existing

• Geometric design

• Roadside conditions

• Traffic operations

• Pavement and drainage structures

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Major Issues Found in the AASHTO Guide of Flexibility in Highway Design

• Published in 1997 & 2004

• Importance of establishing “purpose and need” early in plan development

• Key decisions made early in design process

• Basic design controls are choices made by engineers

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“Risk Management Best Practices”

• 2007 publication of FHWA• Adopted by VDOT in 2008

• Offers engineer a better understanding of the operational and safety effects of potential design exceptions

• Discusses proven, effective mitigation strategies

• Importance of documenting the design exception and mitigation approach

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“Bridging” Flexibility in Highway Design

AASHTO/FHWA “A Guide for Achieving

Flexibility in Highway Design” 12

Engineering is a Balancing ActBalancing Competing Objectives

• Safety• Operations• Standards• Costs• Environmental

Impacts• Stakeholders• Quality• Risk• Laws/Regulations

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AASHTO Flexible Design Policy

“As highway designers, highway engineers strive to provide for the needs of highway users while maintaining the integrity of the environment. Unique combinations of design requirements that are often conflicting result in unique solutions to the design problems”

“...Sufficient flexibility is permitted to encourage independent designs tailored to particular situations.”

Source: Foreword, p. xliii, 2004 Edition

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Know how to use the Green Book

“The intent of this policy is to provide guidance to the designer by referencing a recommended range of values for critical dimensions. It is not intended to be a detailed design manual that could supersede the need for the application of sound principles by the knowledgeable design professional. Minimum values are either given or implied by the lower value in a given range of values. The larger values within the ranges will normally be used where the social, economic, and environmental (S.E.E.) impacts are not critical.‟

Green Book Foreword, pg xliii 15

What Flexibility is in the Green Book?

• Many dimensions and values are shown as ranges• Many criteria described as “guidelines” or “typical”• Many concepts are not dimensioned and discussed

only in functional terms• In many cases, choices are offered for how to

complete a design

• Solutions or concepts not specifically

included are not precluded• Specific solutions are not mandated• Designer judgment is implied or

explicitly suggested

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Application of Design Exceptions

• Designers should understand that design exceptions are an acceptable and useful tool when all standard design solutions are exhausted.

• Acceptance of design exceptions should not be viewed as an admission of failure

• Designers should avoid labeling a number outside of the “norms” as unsafe

• A properly documented design exception is essential for achieving flexibility in design

• Lack of supporting information, inadequate guidance, limited resources, and requests made too late in project development can all pose potential problems in the approval of a design exception 17

Risk Management of Design Exceptions

• Understand the operational and safety effects of any potential DE• What is the potential risk of

the DE• Employ proven, effective and

applicable mitigation strategies as outlined in the Mitigation Strategies Manual

• Fully document and mitigate the DE• Serves to justify the

decision and manage agency risk 18

Analyzing Roadway Safety

•Provides tools for considering safety in the project development process•Assists practitioners in selecting countermeasures and prioritizing projects•Compare project alternatives•Quantify and predict the safety performance of roadway elements

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Safety Has Two Dimensions

• Nominal Safety• Examined in reference to compliance with standards,

warrants, guidelines and design procedures• Comparing geometric design features (lane/shoulder, SSD,

grades) to prevailing design standards (Green Book) • If a roadway meets minimum design criteria it is said to be

nominally safe

• Substantive Safety• Is the expected or long term safety performance for a

roadway• Define the nature/extent of safety problem by frequency,

type, severity of accidents

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Defining the Safety Problem

• Not every location is a “high accident” site.

• Understand types and patterns of accidents; focus on more serious accident types

• Not all “nominally unsafe” roads have substantive safety problems

• Substantive safety may not be a problem on any given project

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Tort Risk

• Adherence to a standard does not automatically demonstrate reasonable care

• Deviation from a standard does not automatically demonstrate negligence

• A structured process for evaluating, approving and documenting the rationale for key decisions is necessary to address professional responsibility and tort liability

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• Route 633 over Garnett Creek located in Fredericksburg District

• The bridge and approach work was constructed in the last few years.

• How could VDOT have altered the design of the project to maximize the flexibility within our standards?

Example Situation

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• Bridge Replacement over Garnett's Creek•Bridge sufficiency rating 29.9

• Rural • Un-posted speed limit• Accident report shows 1 crash in last 6 years• Speed study shows that 85th percentile is 52 mph.• Existing two way road – 16’ width• Existing Bridge – 21’ width• Existing 2’ shoulders, 2’ front width ditches• Road can be closed during construction

Project Background

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• Rural Collector • Existing Year ADT 550 vpd• Design Year ADT 800 vpd• Truck Percentage 2.5%• Design Speed 55 mph• Lane Width 11’• Shoulder Width 5’• Front Ditch Width 6’• Front Ditch Slope 4:1• Bridge Width 28’

Proposed Typical Section

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Existing Bridge and Approaches

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3R Standards

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So, What Really Was Built?

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Bridge Typical Section

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As-Built

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What Would You Have Done Differently?

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Route 633 over Garnett’s Creek• Could we have applied more context sensitivity or

practical engineering concepts?• Utilize 3R vs. GS-3• Shoulder width – Applied 2’ shoulders vs. 5’• Ditch width – 3’ at 3:1 vs. 6’ at 4:1• Lane width – 10’ vs. 11’• 3R site prep for GR-9 vs. full site prep• Bridge width 26’ vs. 28’• Reduced footprint, better context sensitivity

Conclusion

• VDOT and AASHTO provide ample flexibility regarding the use of geometrics • Are you applying that flexibility?

• Understand how and when the Green Book (or other AASHTO/VDOT references) applies • How often do you and/or your staff read/utilize these

references?• Understand that as a designer you have a multitude of

engineering choices available • There is never only “one solution to a problem”

• Stay committed to your decisions but flexible in your approach

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Questions?

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