7.5.1 Final Horizontal/Vertical Alignments

Finalizing horizontal and vertical alignments is necessary before proceeding into detailed roadway design and plans development. Environmental impact minimization, safety enhancement, operational improvement and constructability are elements that must be considered during this process. Drainage headwater elevation and hydraulic grade lines are also important determinants in setting roadway profile grades.
Issues that may warrant modifications include final design of superelevation rates, stopping sight distances (SSD), intersection geometry, grades, access connections, traffic management during construction, major utility adjustments, and drainage facilities. Changes may also be required for minimizing impacts to Section 4(f) properties, wetlands, ROW and threatened or endangered species.
Finalizing horizontal/vertical alignments is an iterative process with drainage design. Design considerations for drainage facilities may require curve or profile grade changes. This task should be coordinated closely with the drainage engineer.
Tasks to be completed in developing final horizontal/vertical alignments include:
  • Evaluate the 3D model for preliminary alignments, including tie-ins at access connections;
  • Evaluate preliminary alignments for opportunities to minimize environmental impacts and enhance constructability;
  • Ensure compliance with basic design criteria;
  • Ensure sight distance criteria is maintained at intersecting roads and driveways;
  • Check construction staging when setting profiles to reduce large differences in grade during construction if possible;
  • Ensure drainage considerations are addressed by adjusting roadway grades and curves with regard to hydraulic grade lines;
  • Verify stream crossing elevations and hydraulics (i.e., set roadway profile to account for bridge structure depths and low chord elevation);
  • Evaluate construction staging for major drainage structures in setting alignments and profiles;
  • Carefully design intersection grading to accommodate drainage structure headwater elevations;
  • Ensure that proposed ditch capacity is adequate; the interrelated elements of ditch capacity, roadside slope safety, and roadway grade need to be properly designed to provide a safe facility; and
  • If the job is in a tidal area, consider storm surge (tide) analysis.