Automated Machine
Guidance: Electronic Files
and Design Data
AASHTO Subcommittee on Construction Meeting
August 18, 2010 – Burlington, VT
Mark Taylor
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Cross-Sections vs. Surfaces
• We traditionally design and build accurately at
each cross-section
• We now have the capability to design and
build accurately everywhere
• However, construction can only be as
accurate as the survey data and controls
• Construction control tolerance is not any more
precise than the design 3D surface model
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Design Today: Cross SectionBased 3D Design Modeling
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3D Design Surface Layers
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Finished surface (top of pavement)
Aggregate base (bottom of pavement) to foreslope
Aggregate subbase layers (if any)
Subgrade surface from slope stake to slope stake
Subexcavation or wall foundations (undercut)
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3D Design Model Work Flow
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Develop the geometric design information
Prepare cross sections for design model
Generate 3D design surface model (TIN)
Check the 3D surface tolerances
Verify the 3D surface path
Spot check xyz of the TIN
Clip the existing terrain and merge the design
and terrain surface models
• Export the combined 3D surface models
– Generate file formats for the Contractor
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Electronic File Formats
• ASCII (generic software)
• Land XML (Topcon software)
• Trimble (Trimble Terramodel and Sitevision
software)
– Trimble .TTM format
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Pattern Lines for
3D Design Model
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Pattern Lines for 3D Model
• Interval spacing is dependent on the radius of
curvature
• Add sections at the beginning and end of
superelevation transitions
• At begin and end of widening transitions,
including for traffic barrier terminals
• At begin and end of road approach
intersections
• Changes in ditch configuration and inlets
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Chords Between Sections
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3D Design Model Tolerances
Design Element
Horizontal
(X and Y
coordinates)
Vertical
(Z coordinate)
Roadway template
points
±0.04 ft
±0.01 ft
Roadside ditch and
other slope points
±0.1 ft
±0.05 ft
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Rec’d Pattern Line Spacing
Pattern Line
Spacing*
Horizontal Curve
Radius
Vertical K Value
10 ft
≥ 300 ft and tangents
≥ 13 and tangents
5 ft
75 ft < 300 ft
6 < 13
2 ft
< 75 ft
<6
*Also at centerline points (PC, PT etc.) and at superelevation
and widening transitions for final design
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Cross-Sections for
3D Design Model
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Template Surface Points
Subgrade Layer
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Connect Similar Cross-Section
Point Labels Using Breaklines
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Transitions (Cut to Fill)
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Cut to Fill Breaklines
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An Ideal World
• The Design engineer provides the Contractor
a complete 3D model that fits site conditions
• Contractor easily loads 3D surface model
directly into the machine guidance system
• The Contractor builds project accurately to the
plans, specifications, and tolerances
• Any changes or revisions are updated in the
3D surface model by the project engineer
• As-built 3D surface model is given back to the
owner (State DOT)
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The Real World
• Existing ground data does not match to site
conditions or with 3D design surface model
• Missing data, information and details about
exceptions to the model
– Lack of detail at intersections and culvert inlets and
outlets requires manual adjustments and warping
– Ditch profiles do not match with culvert inlets or
site conditions
– Special ditch information is shown in the plans
profile but is not in the 3D design surface model
• Specifications do not fully address the work
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Design Changes for 3D/AMG
• Cross section pattern lines at closer intervals
(typically 10-feet instead of 50-feet) to achieve
the required accuracy in the 3D surface
• Proficiency with special applications of the
design software to generate the 3D surface
• Time-intensive activities associated with these
new applications are:
– Hand–editing any cross-sections that cannot be
drawn with standard criteria (modify text search)
– QC checks of the 3D surface between pattern lines
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Changes for 3D/AMG cont’d
• Contract special provisions
– How to resolve discrepancies between the
electronic data and the contract plans
– Responsibility for changes to electronic data
• Achieving a common understanding of the
concepts and limitations in the design model
– Exceptions (what is not modeled)
– Degree of accuracy and precision
– Discontinuities (linear changes and transitions)
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Construction Changes for AMG
• Understanding the concepts and limitations of
the electronic 3D design model (exceptions,
degree of accuracy)
• Understanding the AMG accuracy limitations
• Performing the necessary layout, inspection
activities with less “wood in the ground”
• Using suitable survey equipment and methods
for layout, inspection activities, and for
independent QA of the Contractor’s AMG
methods
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Challenges for 3D Design
• Modeling guidance and training is needed
• Standards for the 3D model deliverables
– Design data files that are provided
– Electronic data formats
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Professional liability/Engineer of record
Consistency, uniformity, quality control
Quantities calculation and documentation
QA/QC of 3D data (DTM, design data files)
Field verification and changes to design data
Documentation of as-built project features
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RRR Projects: Challenges for
3D Design Modeling
• Procedures and specifications for using
design models derived from resource-grade
survey and mapping technologies
• Develop end-result, performance based
methods and specifications for control, rather
than strict line and grade position
• Allow flexibility and foster innovation
• Expedite production and reduce costs
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Standards and Procedures
• When to develop 3D design
models for AMG?
• How to develop the model?
– What features to include?
– How many layers?
– What level of detail?
• What format to provide the
model for others to use?
• How to manage changes to
the as-built design model?
• How to document and
retain electronic records?
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Caution: Automated Computer
Design Plus Machine Guidance
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