7.5 Roadway Design

This section discusses tasks necessary to finalize horizontal/vertical alignments; intersections and driveway design; earthwork of the proposed facility; bicycle and pedestrian facilities and additional details related to the roadway design. Refer to the RDM for design criteria required for the specific roadway functional classification and context classification.

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.

7.5.2 Intersections and Driveways

Intersections and driveways are designed to clearly show pavement contours, profile grades, drainage, locations of sidewalks, pedestrian ramps, pavement structure, and limits of construction.

Frequent access points cause both operational and safety issues. Ensure the driveway spacing is as large as possible and shared access for neighboring facilities has been explored during project development, per TxDOT’s Access Management Manual (AMM). Tight spacing between driveways causes operational and safety issues which are exacerbated when multiple access points to one facility are present. Per the AMM, “as access density increases, crash rates increase”.

7.5.3 Earthwork

Earthwork quantities should be developed from the 3D model using the final alignments. Side slopes and ditch grades should be evaluated and modified to provide a safe and economic design. Special attention should be paid to the tie-ins at intersections and driveways.

7.5.4 Bicycle and Pedestrian Accommodations

Preliminary bicycle and pedestrian facilities planned in preliminary engineering (see

Section 4.4.1.4

) should be finalized to provide safe passage for these modes of transportation. Bicycle and pedestrian facilities that have independent alignments (e.g., shared use paths (SUP) and separated bike lanes) will require their own layout sheets. The RDM provides extensive discussion and guidance on the use and design of bicycle and pedestrian accommodations.

For situations where bicycle and pedestrian bridges are independent structures from those mentioned in

Section 7.8

, reference AASHTO’s LRFD Guide Specifications for the Design of Pedestrian Bridges
for guidance on design elements and standard requirements.

7.5.4.1 Texas Department of Licensing and Regulation (TDLR) Inspections

If total bid items for all pedestrian elements (new or removed signals, pavement markings, walkways, ramps) are greater than $50,000
, the plans must be reviewed and registered according to the requirements of TDLR. CST has contracts with a Registered Accessibility Specialist (RAS) to perform the needed reviews prior to letting and inspections during construction for TxDOT projects. All TDLR fees and RAS fees are paid by CST

Refer to CST’s Construction Contract Administration Manual (CCAM)
and T
DLR Construction Accessibility Requirements Procedures
document for details on submitting plans for review to TDLR. Refer to TxDOT’s PS&E Preparation Manual for details on items to include on the Title Sheet of the plans.

The plan submittal should be made to the RAS at least two months (preferably three months) before advertising the project in case the plan review results in significant revisions.