Precision Standards

Both Schematic and Plans, Specifications, & Estimates (PS&E) surveys shall follow the same precision standards. Level of Accuracy (LOA) identifications come from the
U.S. Institute of Building Documentation LOA Specification Guide V. 3.1
. All Digital Delivery project require higher data density than normal projects, and are specified separately. These standards are below:
  • Horizontal accuracy error allowance:
    • Bridges and other roadway structures: less than 0.1 feet, which is within LOA20.
    • Utilities and improvements: less than 0.2 feet, which is within LOA10.
    • Cross-sections and profiles: less than 1 foot.
    • Bore holes: less than 3 feet.
  • Vertical accuracy error allowance:
    • Multi-phase bridges: less than 0.02 feet, which is within LOA30.
    • Single-phase bridges and other roadway structures: less than 0.04 feet, which is within LOA30.
    • Utilities and improvements: less than 0.1 feet, which is within LOA20.
    • Cross-sections and profiles: less than 0.2 feet, which is within LOA10.
    • Bore holes: less than 0.5 feet.
The guiding principle for point density is to capture all significant detail where it exists, ensuring that the collected data accurately reflects the ground surface and feature geometry for high-fidelity traditional or digital delivery.
  • Spatial density requirement:
    • Manmade features: Maximum distance between measurements is 25 feet; reduce spacing along curves, breaklines, and areas with rapid elevation change to ensure accurate representation where geometry or slope varies significantly.
    • Natural features: Maximum distance between measurements is 50 feet; reduce spacing in irregular terrain or where detail is needed for high-fidelity modeling.
  • Digital Delivery project raw data collection spatial density requirements:
    • TxDOT features: Maximum distance between measurements is 5 feet; reduce spacing along curves, breaklines, and areas with rapid elevation change to ensure accurate representation where geometry or slope varies significantly.
    • Improved features: Maximum distance between measurements is 10 feet; reduce spacing along curves, breaklines, and areas with rapid elevation change to ensure accurate representation where geometry or slope varies significantly.
    • Natural features: Maximum distance between measurements is 50 feet; reduce spacing in irregular terrain or where detail is needed for high-fidelity modeling.
It is the responsibility of the surveyors to understand the capabilities of the measurement devices used for the survey. Recommended practices and procedures are provided in the
TxDOT Surveyors’ Toolkit
. TxDOT District Survey Coordinators shall randomly check data using the recommended practices and procedures to ensure compliance. The surveyor is responsible for reacquiring all data for a survey that does not satisfy the random checks.