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Section 5: Geometric Schematic

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Overview

This section discusses the process of refining alignments and geometrics, performing analyses on geometrics, and preparing preliminary plans and layouts. Most of the data collected and calculated is shown on a “geometric” schematic - a schematic having computed alignments. Work related to schematic development includes performing hydraulic studies, determining right of way needs, and identifying utility conflicts.

After developing preliminary schematics and performing associated preliminary design, the project cost estimate and, sometimes the project scope are updated to reflect changes.

Requirements for presentation of information in schematics are included in the Roadway Design Manual.

Developing the Geometric Schematic includes the following tasks. All tasks should be performed concurrently as much as possible. However, the following sequence of work tasks will likely be necessary:

20500. Develop preferred geometric alignment

20505. Perform preliminary geotechnical surveys

20510. Prepare pavement design report

20515. Refine typical sections

20520. Consider impacts on historic structures

20525. Perform detailed Level of Service analysis

20530. Determine guide signing and operational controls

20535. Submit requests for new or revised access points to interstate highways

20540. Perform preliminary planning for commercial motor vehicle inspection stations

20545. Perform preliminary planning for bridges

20550. Establish preliminary retaining or noise wall locations

20555. Perform hydrologic study

20560. Perform preliminary hydraulic analysis/design

20565. Determine right of way and access needs

20570. Identify existing utilities on geometric schematic

20575. Identify potential utility conflicts

20580. Establish preliminary illumination locations

20585. Evaluate Intelligent Transportation System (ITS) needs

20590. Conduct constructability review

20490. Update cost estimates

20595. Update project scope

10400. Review scope, cost, and staff requirements of project development

Anchor: #i1020842

20500: Develop preferred geometric alignment

Description. A preferred geometric alignment is developed after preliminary schematics are developed and a preferred alternative selected. Related disciplines should be consulted in reviewing alternatives and establishing the preferred alignment. See Task 20450: Evaluate geometric alternatives.

Changes to the preferred alignment after a public meeting or hearing may require TxDOT to repeat the review and approval process for the environmental document and hold an additional hearing. However, minor adjustments to alignments may be made by the designer, if the change is feasible and does not compromise project design criteria. Substantial changes to an approved schematic will require submission of the revised schematic to the Design Division. If FHWA is the agency responsible for oversight, contact Design Division for required submittal documents.

Items to show on a schematic are available in the TxDOT Roadway Design Manual.

Pertinent Project Types. New location, added capacity, or controlled access projects or projects requiring an environmental impact statement.

Helpful Suggestions.

Responsible Party. Project manager

Resource Material.

Anchor: #i1020926

20505: Perform preliminary geotechnical surveys

Description. Preliminary geotechnical surveys are performed to help guide early project layout and design, and to determine feasibility of the preliminary design and limitations on construction staging.

Preliminary geotechnical testing serves as a preview to determine the following factors:

For large structures, preliminary geotechnical surveys form the basis for more rigorous testing. On major projects, a small number of preliminary borings should be obtained to aid in preliminary project layout.

Geotechnical surveys for pavement design should be done at this time and may include roadway pavement testing such as Falling Weight Deflectometer (FWD) testing.

Pertinent Project Types. All projects except preventive maintenance and restoration projects.

Responsible Party. Project manager

Subtasks.

    Anchor: #CJWFMSES
  • Determine needs for more data and field testing after evaluating existing geotechnical information.
    • Anchor: #YUGTYDJN
  • Forward the information to the district pavement engineer, structural engineer, and landscape architect for their use.

Helpful Suggestions.

    Anchor: #HWBGGFJJ
  • Bridge Division Geotechnical Branch is available for geotechnical engineering support in areas of foundations, retaining walls, embankment stability including slope stability and settlement, and stabilization of soft soils under roadway and embankment.
    • Anchor: #SEWTEIHU
  • Construction Division Materials & Pavement Section (CST-M&P) is responsible for technical support for pavement design such as falling weight deflectometer, ground penetrating radar, dynamic cone penetrometer, and seismic pavement testing.
    • Anchor: #MDGUUIKS
  • Construction Division Geotechnical, Soils, & Aggregates Branch is responsible for assisting with soil and aggregate exploration and testing.
    • Anchor: #NJNKBFTJ
  • A right of entry or other written evidence of permission must be obtained before entering private property. See Task 20230: Obtain right of entry.
    • Anchor: #YBBWICUM
  • Survey results may influence project design (e.g., high water table, hazardous materials).

Critical Sequencing.

Resource Material.

Anchor: #i1021074

20510: Prepare pavement design report

Description. The pavement structure represents one of the single most costly items in a typical highway project budget. The objective for doing a preliminary pavement design is to select a pavement structure capable of carrying traffic loads safely, comfortably, and with minimum physical deterioration. Pavement design should be done early in project development to ensure a balance between risk management and adequate funding. Early pavement selection improves estimate accuracy.

A pavement design and pavement design report are required for the following projects that are over 500 ft. long:

A preliminary pavement design conference is used to refine initial concepts, guide the district pavement engineer, and permit development of an approved design and a pavement design report. The pavement design engineer evaluates various data to determine a proper pavement structure, including materials properties, environmental conditions, availability, and cost. Traffic data and geotechnical data should be reviewed. There are benefits and costs to be considered in selecting rigid pavement or flexible pavement types. The designer's job is to assess all facts and factors and maximize the benefits including life–cycle costs and user delay costs. A new design is not necessary if analysis of traffic, environmental conditions, and subgrade yield similar results to a previously approved design. See Task 10430: Obtain Traffic Data and Task 20505: Perform preliminary geotechnical surveys.

The designer must determine the purpose of the new pavement structure, such as improving structural capacity or improving functional characteristics such as ride quality or skid resistance. For overlays and rehabilitation projects, it is essential to perform pavement evaluations to identify the types of distress (such as base failures, asphalt stripping, pumping, etc.), determine the causes for distresses, and suggest a rehabilitation strategy that will address the problem. For new pavements it is important to perform a full geotechnical investigation to determine whether there is a need for stabilization of the subgrade material in accordance with the stabilization guidelines developed by CST–M&P.

If significant changes occur during project development in project scope, pavement type, traffic data, etc., the report may need to be revised and resubmitted.

Pertinent Project Types.

Documentation is required for the project types below; however, HMA 2 inches or less and considered preventative maintenance does not require documentation.

For project types not listed above, contact the district pavement engineer.

Responsible Party. Roadway design engineer or district pavement engineer

Subtasks.

    Anchor: #QVYHOGGU
  • Collect necessary data, such as the following:
      Anchor: #RSLOVKUF
    • “As-built” construction plans; field evaluation data
      • Anchor: #YSLKGEYB
    • Request existing and projected traffic data early in project development. See Task 10430: Obtain Traffic Data.
      • Anchor: #DDTPVFWN
    • Geotechnical investigation
      • Anchor: #IBVWFQCJ
    • Current pavement construction cost information
      • Anchor: #LGUOMCAU
    • Drainage data
      • Anchor: #XANRWNSS
    • Historical performance information
      • Anchor: #XNTSYAMP
    • Pavement evaluation
      • Anchor: #QPOHQITJ
    • Available funding.
      • Anchor: #BJFHANEV
    • Contact district maintenance personnel for additional information on roadway pavement history.
      • Anchor: #DPYMJBDL
    • Check the TxDOT mainframe program, Pavement Management Information System (PMIS), for historical data on pavement conditions.
      • Anchor: #FWPOGODA
    • Perform a condition survey site visit to assess pavement surface distress.
      • Anchor: #HCXTVJIM
    • Determine new pavement requirements - what loads must it carry and how long before the first overlay will be required.
      • Anchor: #KEDJFPKW
    • Determine the type of pavement to be built.
      • Anchor: #MBMOQYFD
    • Determine the different materials to be used for the different layers of the pavement structure.
      • Anchor: #CCSKSKVY
    • Determine the Performance Grade (PG) to be used for hot mix asphalt (HMA) layers.
      • Anchor: #RPNMBIVJ
    • Determine the pay schedule to be used for evaluating the ride quality.
      • Anchor: #RRDFLNWH
    • Perform a life-cycle cost analysis as part of using automated design software (e.g., Flexible Pavement System FPS19).
      • Anchor: #HDWCRHDL
    • Prepare the pavement design and develop a Pavement Design Report.
      • Anchor: #BYMQDJYU
    • Send the design to the district pavement engineer for review and approval. The district pavement engineer is responsible for ensuring compliance with FHWA and TxDOT design policies and procedures. If a district does not have a certified pavement engineer, then pavement design approval reverts to the Materials and Pavement Section of the Construction Division (CST-M&P).
      • Anchor: #XGUXBDPW
    • The district pavement engineer sends the approved copy of the pavement design report to the Pavement Section of the Construction Division for review and analysis. Revise the project cost estimate since pavement is a major portion of the project cost. See Task 20490: Update Cost Estimates.

Helpful Suggestions.

    Anchor: #JXDSCQKW
  • Contact Transportation Planning and Programming Division for both existing and projected traffic data. See Task 10430: Obtain Traffic Data.
    • Anchor: #APMXSMFA
  • CST-M&P is available for assistance as needed.
    • Anchor: #IBNHPXHT
  • Contact the CST-M&P, through the district pavement engineer, for information on the FWD testing, the dynamic cone penetrometer test, the use of ground penetrating radar, and for a pavement design report format.
    • Anchor: #AIPDYRWG
  • The district laboratory can run the triaxial test, Atterberg Limits, and calculate potential vertical rise as part of the geotechnical investigation.
    • Anchor: #UWLVMCCP
  • For large, complex projects that take years to design, the pavement design may need to be re-evaluated during detailed design. It is possible for traffic counts and patterns to change enough to require pavement design change.
    • Anchor: #BQAKVFQF
  • Soil types, weather conditions, and material availability vary widely among districts. Consult with the district pavement engineer and construction engineers before starting a design.
    • Anchor: #IJETLMBB
  • Pavement design must consider potential effects of groundwater on pavement performance along with other factors such as proposed roadway grades.

Critical Sequencing.

    Anchor: #DHVOPUGS
  • Purpose of pavement design is to estimate the cost of pavement related items; pavement design should be performed before updating the cost estimate.
    • Anchor: #VDMURVMB
  • Pavement design task should occur after collecting traffic and geotechnical data, roadway pavement testing and after setting preliminary grades. See Task 20505: Perform preliminary geotechnical surveys.

Authority.

Resource Material.

Anchor: #i1021309

20515: Refine typical sections

Description. As the project progresses, a preferred design alternative is selected, and revisions are made to the design. Typical sections need to be updated to show those changes. Information on their requirements is available in this manual. Design criteria for features to be shown on the typical sections can be found in TxDOT's Roadway Design Manual. If preliminary pavement design information is available at this time, it may be added to the typical section. See Task 20510: Prepare pavement design report and Task 20460: Develop typical sections.

Review proposed typical sections with local public agencies responsible for cost participation in the project.

Pertinent Project Types. All projects

Responsible Party. Roadway design engineer

Critical Sequencing.

    Anchor: #XQOEODWD
  • Revisions to the schematic are determined as the schematic is refined, hydraulic studies are performed, and a detailed Level of Service analysis is done.

Resource Material.

Anchor: #i1021348

20520: Consider impacts on historic structures

Description. A mitigation plan may be needed for projects affecting buildings, structures (including bridges), sites, etc., which are included, or eligible for inclusion in the National Register. If a plan is needed, the project manager should begin considering how mitigation plans will be incorporated into the project.

Pertinent Project Types. All projects except preventive maintenance and restoration projects

Responsible Party. Project manager

Helpful Suggestions.

    Anchor: #IMCAHGNA
  • Coordinate all development with the district environmental coordinator.
    • Anchor: #QBLXXUXR
  • Request that the landscape architect review the mitigation plan so that landscape and aesthetics are considered.
    • Anchor: #UIJJQEXA
  • The Environmental Affairs Division will coordinate with the State Historic Preservation Office, which will review the PS&E package for all projects involving historic buildings, structures, or landscapes.

Authority.

Resource Material.

Anchor: #i1021454

20525: Perform detailed Level of Service analysis

Description. Earlier in the process, a preliminary Level of Services (LOS) analysis of project alternatives should have been performed to aid in selecting a preferred alternative. See Task 20410: Perform preliminary Level of Service (LOS) analysis.

At this stage, a detailed LOS analysis may be needed to compare different geometrics to refine the design proposal. For example, the analysis can be used to refine geometrics such as shoulder and lane widths, profile grades, and frequency of access points.

Results of the detailed LOS analysis are incorporated into establishing preferred alignments. See Task 20500: Develop preferred geometric alignment and Task 20515: Refine typical sections.

A LOS analysis is usually performed for the current year using current traffic and geometric conditions, and for the future “design” year using traffic projections and proposed geometric designs. The LOS analysis may show whether a proposed design will meet future transportation needs.

Pertinent Project Types. New construction and reconstruction projects on multi-lane highways and freeways, and projects with ramp modifications

Responsible Party. Roadway design engineer

Subtasks.

    Anchor: #OEJIEHFM
  • Review traffic data obtained on present and projected traffic volumes and other data such as percent trucks, design hourly volume, and the directional distribution. See Task 10430: Obtain Traffic Data.
    • Anchor: #BJXXBBPY
  • Obtain data on current and proposed roadway features (e.g., number of lanes, offset to obstructions, lane widths).

Helpful Suggestions.

Critical Sequencing.

    Anchor: #LDCPLCIS
  • Perform as part of refining the preferred alignment and geometrics.

Resource Material.

Anchor: #i1021540

20530: Determine guide signing and operational controls

Description. Traffic control guide signs guide vehicle operators along streets and highways. Guide signs show route designations, destinations, directions, distances, services, points of interest, and other geographical, recreational, or cultural information.

There are different types of guide signs used on freeways or expressways. These include advance signs for interchange exits, supplemental signs, exit direction signs, diagrammatic signs, and miscellaneous signs.

The department has the authority to install, maintain, and operate traffic signals on the state highway system and may install operational controls in incorporated and unincorporated areas provided they meet specified agreement conditions.

Pertinent Project Types. Mainly freeway/expressway and arterial highway projects; however, there are some rural applications.

Responsible Party. Roadway design engineer or traffic engineer

Authorization.

Subtasks.

Helpful Suggestions.

    Anchor: #QXRJGLPY
  • Design guide signs to be legible to drivers approaching them and to allow adequate time for the driver to respond.

Critical Sequencing.

Resource Material.

Anchor: #i1021629

20535: Submit requests for new or revised access points to interstate highways

Description. Regardless of funding or oversight, new or revised access points on interstate highways must be approved by the Federal Highway Administration (FHWA). Revised access is considered to be a change in configuration even though the number of actual points of access may not change. Each entrance, exit, “locked gate”, new or modified freeway-to-crossroad interchanges inside a transportation management area, ramp, or access to a collector-distributor is considered an access point. Locked gate access in remote areas may be allowed in special circumstances for emergency management, border patrol, utility, or maintenance forces. FHWA must ensure there is either no or only minimal adverse effect on the operation of the interstate facility.

The Request is an agreement between a state department of transportation (TxDOT) and the controlling federal agency (FHWA). The report front cover should only show the TxDOT logo, project information, and location. Preparer information (TxDOT District, local agencies, or Consultant) and all associated logos may be placed on an acknowledgment page in the Appendix. Any information in the body of the report shall be presented as a TxDOT request. Reports will be rejected by FHWA, if the request and recommendations are attributed to a TxDOT District, local agencies, or Consultant.

A request for access modifications must be documented in an “Interstate Access Justification Report (IAJR)” which is considered a stand-alone document; reference to decision making information in other documents is discouraged.

The IAJR should provide information to support a request for the approval of new or revised points of access on completed sections of the interstate system. Establish areas of influence for the proposed change in access. At minimum, interstate area of influence should be done between the nearest upstream and downstream interchanges and crossroad or local roadway area of influence should be between the first traffic signal each side of a major intersection to ensure the ability to collect and distribute traffic. Provide Level of Service analyses. See Task 20525: Perform detailed Level of Service analysis.

Submit one schematic layout, DSR Form 2440, Form 1002, and one IAJR to Design Division Field Section for preliminary submittal review and comments. The project has to be acceptable in terms of safety, environment, design, and operation. Any revisions or corrections will be addressed before the department can submit an IAJR recommendation for approval to FHWA.

FHWA must preapprove concurrent reviews with the department. Concurrent reviews are allowed, if there are emergency circumstances.

See FHWA Delegation of Authority link, under Resources below. Contact DES Field Section for actions indicated in the “N/A” column. Provide the following for the final IAJR submittal:

Pertinent Project Types. Projects involving new mainlane access points, revisions to existing access points, or abandonment of ramps or interchanges on the interstate system.

Responsible Party. Project manager

Helpful Suggestions.

    Anchor: #FLKRTGUI
  • Consider including a line diagram showing LOS results and traffic volumes.
    • Anchor: #QDWJHJCW
  • Informal coordination with FHWA during schematic preparation may streamline the FHWA review process later.
    • Anchor: #LNBBVFJF
  • Concurrent reviews with the department and FHWA require prior approval from FHWA.
    • Anchor: #BSJSMDSU
  • Anticipate about 60 days for coordination and approval of the IAJR by FHWA Headquarters staff in Washington, DC.
    • Anchor: #FNGGVYQB
  • Report may be evaluated by persons unfamiliar with the project location. Do not use multiple names or local name references for individual roadways.

Critical Sequencing.

    Anchor: #MTTHKWSO
  • FHWA approval is considered a federal action which requires NEPA procedures are followed. Final approval of access cannot precede NEPA completion.
    • Anchor: #AMMAVDSR
  • This task should be done after preparing a schematic.

Authority.

Resource Material.

Anchor: #i1021688

20540: Perform preliminary planning for commercial motor vehicle inspection stations

Description. The need for infrastructure improvements for Commercial Motor Vehicle (CMV) inspection stations and the determination of their location must be coordinated between the TxDOT administration and the Department of Public Safety (DPS). The DPS provides permanent scales, if needed, and also provides manpower to operate inspection stations. Construction of new inspection stations must be authorized by Texas Transportation Commission minute order. Projects that serve existing inspection stations should consult DPS for needed infrastructure improvements as part of the project.

The need for “weigh-in-motion” (WIM) detectors and locations are determined by TPP - Freight and International Trade Office. These detectors are used to gather vehicle information not for law enforcement.

Pertinent Project Types. Individual inspection station projects or highway improvement projects including inspection stations.

Responsible Party. Project manager

Subtasks.

    Anchor: #KLFCISOW
  • Obtain Commission authorization for any new inspection station construction.
    • Anchor: #DBFNLLAE
  • Contact the DPS to obtain details on inspection station design needs, consistent with Commission direction.
    • Anchor: #WYHAFOWT
  • Develop preliminary plans for the inspection station.

Authority.

Helpful Suggestions.

    Anchor: #AIITSWVP
  • Clarify funding issues in question before beginning planning or design.

Critical Sequencing.

    Anchor: #OOHJCNVY
  • If part of a larger project, perform this task when developing other preliminary plans.
Anchor: #i1021743

20545: Perform preliminary planning for bridges

Description. The location of proposed bridges must be determined early in project development. Preliminary planning includes estimating bridge limits, span lengths, and bent locations. Bridge layouts are created from this information and forwarded to the Bridge Division for approval. Accommodations for future bridge widening should be considered at this time.

If a railroad crossing is involved, the Traffic Operations Division - Railroad Safety Section (TRF-RSS) will coordinate with the railroad. Project Development Section of the Bridge Division will review Exhibit A.

Culverts with a total span greater than or equal to 20 feet are considered bridge-class culverts and their design must follow span bridge guidelines.

Pertinent Project Types. Bridge projects or other projects that include bridge class structures.

Responsible Party. Roadway design engineer

Subtasks.

Helpful Suggestions.

    Anchor: #KFTVRIOA
  • Seek input and guidance from Project Development Section of the Bridge Division or the district bridge section concerning bridge types, application limits for bridge types, and possible innovative solutions.

Critical Sequencing.

    Anchor: #LCMLBJHO
  • Bridge planning must be addressed early in project development. Characteristics such as limits of bridge, bent locations, span type and lengths of bridges crossing water can usually be set with strong certainty early in project development. Planning for overpasses, underpasses and interchanges requires an iterative process to satisfy structural capability and horizontal and vertical clearance requirements between roadways and bridges.

Resource Material.

Anchor: #i1021877

20550: Establish preliminary retaining or noise wall locations

Description. Preliminary retaining wall or noise wall locations are established as part of developing geometric schematics. Wall locations may be revised as the project progresses. Locating walls will assist in determining locations of needed soil core borings. See Task 20505: Perform preliminary geotechnical surveys.

The noise study will include recommendations for mitigating noise. A noise wall is the primary method. Later, during detailed design, retaining and/or noise wall layouts will be prepared. See Task 30355: Conduct noise analysis and Task 50800: Prepare retaining and/or noise wall layouts.

Pertinent Project Types. Projects having retaining and/or noise walls

Responsible Party. Roadway design engineer

Subtasks. The following subtasks are common to both retaining and noise walls:

    Anchor: #NEOYOKJX
  • Determine if aesthetics is an important consideration because this will affect the type of design.
    • Anchor: #IURSLRPL
  • If walls are adjacent to residential or school properties, consider the structural design or barriers for crash safety.
    • Anchor: #MKMTGYSD
  • Consider traffic control plan, soil considerations, and right of way limitations because these factors may dictate type of wall to be used.
    • Anchor: #PJVORUUI
  • Determine limitations on access to construct and maintain the wall. This will affect type of wall design (i.e., precast, cast-in-place, drilled shafts, etc.).
    • Anchor: #RPNNXDVL
  • Determine right of way boundaries, and any additional site constraints.
    • Anchor: #KJOOWFCM
  • Coordinate with utility companies to determine any potential conflicts.
    • Anchor: #BOHJTTVX
  • Determine if street lights, overhead bridge signs, concrete traffic barriers, or traffic signs will be attached to the wall.

Subtasks.

Retaining walls:

    Anchor: #WMOWXEDM
  • Determine where walls are needed, and their limits. Compare retaining wall cost to bridge cost to determine height at which bridge is more cost effective.
    • Anchor: #PNIKTHCT
  • On retaining wall layouts, include horizontal and vertical curvature information with stations and elevations along the top and bottom of the wall.
    • Anchor: #CYNFRUWS
  • Determine if the retaining wall also needs to act as a noise barrier wall.
    • Anchor: #RAUTYTNO
  • Determine if concrete barrier is needed at the base of a retaining wall for maintenance reasons (e.g., to protect fragile wall facings) or safety reasons (e.g., to shield vehicles from rough wall facings).
    • Anchor: #UAYIMOAQ
  • Determine if the retaining wall will be supporting traffic lanes. If so, the design must account for traffic loading and barrier affect loading.
    • Anchor: #DFBNKBVE
  • Check sight distance for walls in cut sections at intersecting streets and driveways.
    • Anchor: #QLHUFQHS
  • Submit retaining wall layout to Bridge Division if height will be greater than 25 feet.

Noise walls:

    Anchor: #SUMGGUGY
  • Coordinate with the environmental specialist to determine if a noise analysis and mitigation study is required. If so, determine if one was completed.
    • Anchor: #LJYLVXOS
  • Determine if a noise wall is the recommended mitigation measure for noise abatement. Refer to the project noise analysis and mitigation study report.
    • Anchor: #IHKNAWPK
  • Determine the material type for the noise wall. Material weighing four pounds per square foot is dense enough to prevent noise from passing through it. TxDOT typically uses concrete. Wood is not an acceptable material due to maintenance reasons.

Helpful Suggestions.

For retaining walls or noise walls:

    Anchor: #OCNCNIIH
  • When creating a wall alignment, begin the alignment start point before the wall begins. This will make it easier to revise if, due to roadway or bridge changes, the wall beginning or end is moved.
    • Anchor: #VLSQSQMG
  • Provide adequate clear zone between travel lanes and the wall.
    • Anchor: #CNVQCHIO
  • The wall should not be located in gore areas and should be designed to avoid interfering with sight distance - including sight distance at intersecting streets and driveways.
    • Anchor: #JKBPWUHL
  • Create a smooth profile on the top of the wall for a pleasing appearance.

For noise walls:

    Anchor: #NYMBDYBH
  • Refer to the noise analysis for the location and dimensions of the proposed noise wall.
    • Anchor: #QPLGBYSQ
  • For noise walls adjacent to residential areas and parklands, aesthetics will play an important role in developing the wall. Coordinate with planners, landscape architects and community groups early in project development.
    • Anchor: #VDANCIGQ
  • Often, the placement of the noise wall depends on existing or proposed utility lines. Coordinate early with utility owners to determine locations of existing and proposed new lines.
    • Anchor: #SBRYPGAB
  • Determine if a berm may be effectively used to mitigate noise. It may be used with a noise wall and allow a shorter, more aesthetically pleasing wall.
    • Anchor: #HOMKLAYU
  • Use caution about building noise walls because they might limit future access to adjacent property.

Critical Sequencing.

    Anchor: #MJNEKFXM
  • The noise study must be completed before performing this task.
    • Anchor: #WTCRKWIC
  • Preliminary retaining wall layouts should be submitted, when required, as soon as practical and before detailed design.

Authority.

Resource Material.

Anchor: #i1022150

20555: Perform hydrologic study

Description. A hydrologic study is performed to estimate flood magnitudes caused by precipitation. An analysis will provide the designer with fundamental data necessary to perform preliminary sizing of drainage facilities and bridges. Data compiled includes peak runoff (discharge) and discharge hydrographs.

Pertinent Project Types. All projects except preventive maintenance and restoration projects.

Responsible Party. Roadway design or hydraulic engineer

Subtasks.

    Anchor: #QUWTSSRO
  • Conduct a site investigation. See the Hydraulic Design Manual.
    • Anchor: #TRCWBVUK
  • Identify potential outfall and stream crossing locations.
    • Anchor: #RMSXALHV
  • Estimate the runoff from the watershed. See the Hydraulic Design Manual.
    • Anchor: #UIPXYLQN
  • Review previous hydrologic study, reports, as-built construction plans, bridge inspection reports, and available stream gage data. Obtain and evaluate additional data including hydrologic studies, existing structure and channel surveys, existing structure inspection reports, tidal surveys, soil reports, and wetland reports.
    • Anchor: #HYRLILED
  • Review U.S. Natural Resources Conservation Service (NRCS) reports as well as USGS and FEMA flood maps.
    • Anchor: #AXVGVTQI
  • Verify past coordination with local governments having jurisdiction over the project area.

Helpful Suggestions.

    Anchor: #MLUKPYNI
  • Consider the possibilities for future development in the area. Additional buildings and parking lots can change the rate and direction of runoff.
    • Anchor: #RRINUPJE
  • Many cities maintain zoning and land use maps; these should be referenced when estimating watershed runoff.

Critical Sequencing.

    Anchor: #LJWYUKAE
  • This task should be done after the preliminary roadway layout is determined.

Resource Material.

Anchor: #i1022220

20560: Perform preliminary hydraulic analysis/design

Description. A hydraulic analysis is required to create the preliminary plans and profiles of the roadway. The purpose of the analysis/design is to determine approximate elevations and sizes of cross drainage structures and to establish their effects on the roadway profile. The analysis conducted should result in an estimate of the most efficient, cost-effective drainage facilities that can accommodate the design storm.

The basic hydraulic design process begins with data collection. Ultimately, the type of drainage facilities provided in the hydraulic design will be determined by the highway classification, right of way, geometry, and other considerations. The primary focus at this stage is to balance traffic safety and hydraulic efficiency and to comply with any regulations such as FEMA. Usually, there are not enough funds available to design a facility to handle the biggest flood that would ever occur. Thus, a compromise must be achieved between expense and potential effect.

Other major considerations should be determined, such as the need for large storm drain structures, and detention ponds, pump stations, and other hydraulic facilities; these should be assessed for cost and ROW requirements.

Pertinent Project Types. Projects affecting existing drainage, including those that add a concrete median barrier to an existing facility.

Responsible Party. Roadway design or hydraulic engineer

Helpful Suggestion.

    Anchor: #TBMWPVWQ
  • The calculation process may be significantly easier with use of TxDOT-approved hydrologic and hydraulic computer software. This hydraulic design software is a package of several programs, which provide computational capability for the majority of procedures contained in the TxDOT Hydraulic Design Manual.

Critical Sequencing.

    Anchor: #SDXXOYBU
  • Preliminary hydraulic design can be performed after runoff is calculated.

Resource Material.

Anchor: #i1022278

20565: Determine right of way and access needs

Description. ROW requirements must be determined as part of developing preliminary and geometric schematics. With the geometric schematic, an accurate estimate of the area of ROW to be acquired is used in estimating the project's cost and refining the alignment to optimize use of the ROW. Earlier while developing preliminary schematics for route alternative selection, ROW needs for each route were approximated to compare alternative effects. Known utility facilities within the needed ROW should be located on the schematics.

The roadway design engineer determines the right of way (ROW) needed based on the proposed alignment, typical sections, access control, and any other information available. In determining proposed ROW limits, the engineer should consider accommodation for construction, drainage, clear zone, access to and maintenance of the highway, accessible pedestrian design, if applicable, and environmental mitigation.

Pertinent Project Types. Projects requiring additional ROW or a change to control of access.

Responsible Party. Roadway design engineer

Subtasks.

Helpful Suggestions.

    Anchor: #RFUQGAJG
  • Consider reducing ROW acquisition costs by developing an alignment so that additional ROW is required only from one side of an existing facility.
    • Anchor: #VBUBONQD
  • Proposed ROW should be sufficient for parallel drainage channels and cross-drainage structures.
    • Anchor: #NDPNFKFA
  • Identify needed drainage easements.
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  • Strive to minimize displacements of homes or businesses while still meeting other design requirements.
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  • Intelligent Transportation System (ITS) infrastructure may affect ROW needs.
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  • If any airport ROW is needed, contact the Aviation Division Planning Section for coordination.
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  • If existing features are determined to be an encroachment on department ROW, they will need to be removed.
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  • Reconfiguration of existing ramps may necessitate acquisition of additional control of access.
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  • Disposal of access rights must be handled according to 43 TAC Part 1 Chapter 21.

Critical Sequencing.

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  • A ROW needs determination plays a key role in determining a preferred alignment, because there may be existing ROW and access constraints, especially in urban areas. This task should be performed alongside preferred alignment determination and the related geometrics.

Authority.

Resource Material.

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20570: Identify existing utilities on geometric schematic

Description. The design engineer should obtain information on existing utilities from utility owners and create a layout of the existing utilities. See Task 20250: Obtain information on existing utilities.

Pertinent Project Types. All projects except preventive maintenance and restoration projects.

Responsible Party. Roadway design engineer

Subtasks.

Helpful Suggestions.

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  • A utility layout may be prepared more easily by performing the following steps:
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    • Sending the schematic to utility owners who do not have utility plans readily available
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    • Ask utility owners to draw their utilities on the schematic with distances referenced to the ROW or other reference points
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  • Consider using subsurface utility engineering (SUE). Information is available under Task 40110: Locate existing utilities.

Critical Sequencing.

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  • A utility layout should be created soon after developing the preliminary schematic.
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20575: Identify potential utility conflicts

Description. Utility conflicts refer to physical conflicts between existing utilities and proposed transportation facility construction. Utility conflicts also refer to utilities not complying with TxDOT's Utility Accommodation Rules, such as utilities not complying with location, cover, or clearance requirements. After developing a utility layout, the roadway design engineer can determine potential utility conflicts. If geospatial data is available, do a three dimension model review. Knowledge of these conflicts assists the utility owners in budgeting for anticipated adjustment costs.

Early coordination cuts construction time extension claims and delays, which increase project cost.

Pertinent Project Types. All projects except preventive maintenance and restoration projects.

Responsible Party. Roadway design engineer

Subtasks.

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  • Review preliminary schematic with district utility coordinator.
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  • At minimum, locate utility conflicts in linear plan and profile.
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  • Contact the affected utility owners to discuss plans to address utility conflicts.

Helpful Suggestions.

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  • Try to revise alignments and project features to avoid utilities before requesting that the utilities be moved. It can be expensive and time-consuming to adjust the utilities, so it should be done only when it is unavoidable.
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  • Utility owners should be advised of potential conflicts as soon as possible. One to two years may be needed to budget, design, and complete required adjustments.
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  • If geospatial data is available, do a three dimension model review of utility conflicts.

Resource Material.

Anchor: #i1022544

20580: Establish preliminary illumination locations

Description. Illumination infrastructure must meet the requirements of AASHTO’s Roadway Lighting Design Guide, and must use TxDOT standard equipment and spacing. Electrical systems must be designed in accordance with the National Electrical Code. A preliminary illumination layout should be prepared showing pole locations and power sources. Also provide a layout showing the photometry and foot‑candle reading.

Federal Aviation Administration (FAA) requires notification of construction for above ground level structures planned near airport facilities. Evaluate illumination poles and locations near airport facilities. Submit information to FAA. See Resource Material list below.

The department uses two basic types of illumination systems:

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  • Continuous illumination systems - Mainlanes, direct connectors, ramp entrances and exits, merge and diverge locations
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  • Safety lighting systems - Location doesn’t meet warrant for continuous lighting. Engineer judges a need for safety lighting due to geometric hazard, high crash rates, etc.

Pertinent Project Types. Projects requiring illumination.

Responsible Parties. Roadway design engineer

Subtasks.

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  • Develop plan sheets, pertinent notes, understructure lighting, and details.

Helpful Suggestions.

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  • Install lighting systems on eligible roadways where conditions warrant such installation.
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  • Illumination in residential areas provides safety and security for road and sidewalk users, but should be reviewed to minimize undesirable impacts on residences.
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  • Traffic Operations Division, Illumination Branch is available to provide design assistance, upon request.

Critical Sequencing.

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  • Preliminary cross-sections, locations of proposed roadside barriers, topographic maps and information on existing luminaire locations are needed before lighting plans can be developed.

Authority.

Resource Material.

Anchor: #i1117544

20585: Evaluate Intelligent Transportation System (ITS) needs

Description. Intelligent Transportation System (ITS) uses advanced wireless communications in vehicles and infrastructure to improve safety, mobility, and reduce environmental impact. Real–time data capture and management from vehicles (trucks, transit, cars), ubiquitous mobile devices, and infrastructure improves operating performance of the surface transportation system. Dynamic mobility applications make the system safer, smarter, and greener.

Traffic management centers (TMC) – TMC manages department ITS equipment. Large metropolitan areas have dedicated facilities, operators, and support staff. Smaller offices are managed by operators with other job duties. A TMC works as a central facility with agencies supporting toll collection, vehicular security, enforcement, and safety.

Dynamic Message Signs (DMS) – Controlled by the TMC. Signs inform motorists of emergency weather hazards, travel-related Homeland Security advisories, or any incidents on the highway. During non-incident times, travel time messages are displayed to assist congestion management. Motorists appreciate seeing travel times; it gives motorists the choice to continue on the route or divert to a less congested highway or street.

Pertinent Project Types. Major corridors (urban or rural), toll facilities, and other roadways which would benefit.

Responsible Party. Project Manager

Subtasks.

Resource Material.

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20590: Conduct constructability review

Description. Requirements for construction, including construction phasing, should be considered throughout development of the geometric schematic and preliminary layouts. If needed, seek construction and traffic expertise for assistance.

Use of available advanced modeling technology, including three dimension digital modeling, may help provide a view of construction conflicts and may be required for FHWA FAHP projects greater than one million dollars. Identifying constructability issues reduces change orders and delay costs, which means less inconvenience to the traveling public. Future maintenance problems may be eliminated.

Pertinent Project Types. All projects, except preventive maintenance and restoration projects

Responsible Party. Roadway design engineer

Subtasks.

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  • Develop conceptual construction phasing plan.
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  • Involve multi-disciplinary geometric schematic review relating to functional areas of maintenance, traffic, design, and construction.
    • Anchor: #WGQKIUPR
  • Review requirements for access and operation of construction equipment to ensure that schematic design can be built. Enlist the help of an experienced construction inspector for this review.

Helpful Suggestions.

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  • Sequence of construction often affects selection of retaining or noise walls and bridge construction method.

Resource Material.

Anchor: #i1022769

20595: Update project scope

Description. As project development progresses, the project scope may change due to design refinements, route or design alternative selection, utility conflicts, environmental mitigation measures, input from public involvement, or value engineering analysis findings.

Changes to project scope or other significant changes should be recorded in the Design Summary Report ( DSRform) that was prepared during the Preliminary Design Concept Conference. Updating this Form helps serve as a type of project development “journal.” Recording changes and reasons for them assists in project development, especially if project team members change. See Task 20100: Conduct a Preliminary Design Concept Conference.

Pertinent Project Types. Projects for which a DSR was prepared.

Responsible Party. Project manager

Subtasks.

Resource Material.

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