Flexibilities in VDOTs Design Policies and Standards 2012

Flexibilities in VDOTs Design Policies and Standards 2012 Outline VDOTs 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 2 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 3 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 4 AASHTO/VDOT Flexibilities in Design 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. 5 VDOT IIM 235 (CSS) Emphasize VDOTs 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 6 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. 7 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 8 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 9 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 10 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 11 Bridging Flexibility in Highway Design AASHTO/FHWA A Guide for Achieving Flexibility in Highway Design 12

Engineering is a Balancing Act Balancing Competing Objectives Safety

Operations Standards Costs Environmental Impacts Stakeholders Quality Risk Laws/Regulations 13 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 14 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 16 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 19

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 20 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 21 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 22 Example Situation

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? 23 Project Background 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 24 Proposed Typical Section

Rural Collector Existing Year ADT Design Year ADT Truck Percentage Design Speed

Lane Width Shoulder Width Front Ditch Width Front Ditch Slope Bridge Width 550 vpd 800 vpd 2.5% 55 mph 11 5 6 4:1

28 25 Existing Bridge and Approaches 26 3R Standards 27 So, What Really Was Built?

28 29 Bridge Typical Section 30 As-Built 31 What Would You Have Done Differently?

Route 633 over Garnetts 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 32 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 33 Questions? 34

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