Preserving the Lost Art of Geometric Design: Tools, Techniques and Talent TRB Workshop - January 23, 2011 Understanding the Art Mark Doctor, PE Federal Highway Administration

“Lost Art” ??? Developed by Jack E. Leisch & Assoc.

“The art of modern road building is the result of gradual development to meet changing traffic needs and broadened knowledge gained through experience and research” AASHO, 1954

Freeway Design - Contemporary Art Properly applying the “timeless” principles of good freeway design to modern conditions

What kind of “ Modern ” Conditions? High Traffic Volumes –more lanes –more trucks –longer periods of saturated traffic (congestion) Demands for new interchanges Complex conditions for unfamiliar drivers (rapid succession of decision points) –aging population of drivers Restricted budgets

Right-of-Way constraints Constructability under traffic – Construction sequencing – Maintaining local access – Temporary ramp closures – Maintaining vertical clearances What kind of “ Modern ” Conditions?

“Lost Art” - Key Themes Human Factors Based Design - A quality design is ultimately judged by its ability to be used safely and efficiently by drivers

MAC DONALD MAC DUFF MAC HINERY

Most exit and entrance ramps are on the right-hand side

AASHTO Green Book: “… extreme care should be exercised to avoid left-hand entrances and exits in the design of interchanges.” “Because left-hand entrances and exits are contrary to driver expectancy, special attention should be given to signing and the provision for decision sight distance…”

Is this a left-hand exit ?

“Lost Art” - Key Themes - Design the interchange with consideration of the driver’s perspective - Don’t rely on signing to make the required movements understandable If you can’t sign it properly, then don’t build it!

Complex signing can overwhelm the driver and increase the risk of error in the driving task I-65 north of Nashville, TN

What is the most important page in the AASHTO Green Book? Page 863 – Testing for Ease of Operation Should be completed after the preliminary design - Clarity of paths to be followed - Sequence of the merging, diverging and weaving movements - Practicality of signing “… the designer can visualize exactly what the driver sees …”

FHWA Policy on Access to the Interstate System (revised Aug 2009) Policy: It is in the national interest to preserve and enhance the Interstate System to meet the needs of the 21 st Century by assuring that it provides the highest level of service in terms of safety and mobility. Therefore, FHWA’s decision to approve new or revised access points to the Interstate System must be supported by substantiated information justifying and documenting that decision. FHWA Interstate Access Guide:

The access request must include a conceptual signing plan Sample conceptual signing plan 2009 Revision to FHWA Policy

Effectively dealing with the “ TRADE-OFFS ” for new interchanges: Mobility (net gain or net loss ???) Safety (net gain or net loss ???) Cost (priority level / appropriate use of public funds) Social and environmental impacts Benefit to a variety of users ??? Freeway Design - Contemporary Art - Sophisticated design practitioners understand the many choices involved with developing a project design (flexibility) and base their choices upon understanding the trade-offs

There are always alternatives Understand the tradeoffs among costs, traffic operations, safety and space efficiency – interchange location – interchange configuration – geometric design options – transportation system management options Tailor alternatives to site conditions and constraints (right-of-way, adjacent development, crossroad intersections, overall traffic) “Lost Art” - Key Themes

Many Choices in Interchange Forms Service interchange configurations can differ greatly in terms of: Fitting into the existing conditions and constraints Level of traffic operations and safety provided Pedestrian accommodation Cost/resource requirements

Project Performance vs. Cost Theoretical Relationship: Opportunities for substantial improved performance may exist with modest additional investment in infrastructure enhancement (i.e. construct more lanes, braid ramps, C/D systems, etc.) Cost Performance The realm for applying engineering judgment

Integrate traffic analysis into the design process –A traffic analysis estimates (i.e. statistically predicts) the operational performance of the various segments and elements and allows alternatives comparison in order to make better project decisions Size the freeway, interchange and crossroad (i.e. number of lanes needed) based on design year traffic needs Freeway Design - Contemporary Art

Wisely apply Traffic Analysis Tools Freeway Design - Contemporary Art Utilize a tool that is appropriate for: –The condition being assessed –The available budget –The time allocated –The quality of the input data OR

Traffic Analysis Toolbox

Travel demand forecasting is NOT an exact science – make design choices that consider the potential variability in traffic demands over time Travel Demand Modeling – Key Message Freeway Design - Contemporary Art Make design choices based on a probabilistic range of design volumes

Sample – Traffic Volume Sensitivity Analysis

Freeway Design - Contemporary Art Applying new tools to assess the “safety effects” of design choices Models for predicting the safety effects of design decisions such as –horizontal alignment –vertical alignment –cross-section –cross road intersections

What constitutes “Safe” Design? “ But Captain, it met all design standards” ‘nominal safety’ refers to adherence to applicable design criteria and standards

Safety Risk is a Continuum Crash Risk Design Dimension (Lane Width, Radius of Curve, Stopping Sight Distance, etc.) Nominal Safety Substantive Safety ‘substantive safety’ refers to the actual (or predicted) safety performance of a highway or proposed design

Summary  A quality design is ultimately judged by its ability to be used safely and efficiently by drivers  Test your design for “ease of operation” by the driver  Sophisticated design practitioners understand the many choices involved with developing a project design (flexibility) and base their choices upon understanding the trade-offs  Properly apply the “timeless” principles of good freeway design to modern conditions  Properly integrate available tools into your design decision making process  Traffic analysis tools  Highway Safety Manual

30