Section 5: Geometric Schematic
Anchor: #i1020814Overview
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, Chapter 1, Section 3.
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:
2500. Develop preferred geometric alignment
2505. Perform preliminary geotechnical surveys
2510. Prepare pavement design report
2520. Refine typical sections
2530. Consider impacts on historic structures
2540. Perform detailed Level of Service analysis
2550. Determine guide signing and operational controls
2560. Submit requests for new access points to interstate highways
2570. Perform preliminary planning for weigh stations
2580. Perform preliminary planning for bridges
2590. Establish preliminary retaining and/or noise wall locations
2610. Perform hydrologic study
2620. Perform preliminary hydraulic analysis/design
2630. Determine right of way and access needs
2640. Identify existing utilities on geometric schematic
2650. Identify potential utility conflicts
2660. Establish preliminary illumination locations
2670. Conduct constructability review
2460. Update cost estimates
2690. Update project scope
1400. Review scope, cost, and staff requirements of project development
Anchor: #i10208422500: Develop preferred geometric alignment
Description. A preferred geometric alignment is developed after preliminary schematics are developed (see 2350: Evaluate geometric alternatives) and a preferred alternative selected. Related disciplines should be consulted in reviewing alternatives and establishing the preferred alignment.
Changes to the preferred alignment after a public 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 feasible and if the change does not compromise project design criteria. Substantial changes to the approved schematic will require submission of several copies of the revised schematic to the Design Division/FHWA.
A checklist of items to show on a schematic is available in the TxDOT Roadway Design Manual, Chapter 1, Section 3.
A list of sub-tasks involved in developing a schematic is available in this manual under 2350: Evaluate geometric alternatives.
Pertinent Project Types. New location, added capacity, or controlled access projects or projects requiring an Environmental Impact Statement.
Helpful Suggestions.
- Avoid changes to ROW limits and locations of ramp gores shown on the schematic after Design Division and FHWA approval.
- Consider underground features, such as utilities and septic tank systems, when making alignment adjustments.
- Begin identifying and securing approval of design exceptions/waivers (see 2870: Submit design exceptions/waivers for approval).
- Consider conducting a value engineering study (see 2700: Conduct a Value Engineering (VE) study).
Responsible Party. Project manager
Resource Material. TxDOT Roadway Design Manual
Anchor: #i10209262505: Perform preliminary geotechnical surveys
Description. Preliminary geotechnical surveys are performed to help guide early project layout and design, and to determine 1) feasibility of the preliminary design and 2) limitations on construction staging. Preliminary geotechnical testing serves as a preview to determine the following factors:
- whether an additional final geotechnical survey (see 5460: Perform final geotechnical surveys) is needed.
- preliminary geotechnical surveys can vary from simple, visual inspections to various forms of subsurface exploration, depending on information needed.
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
Sub-tasks.
- Determine needs for more data and field testing after evaluating existing geotechnical information.
- Forward the information to the district pavement engineer, structural engineer, and landscape architect for their use.
Helpful Suggestions.
- The Field Operations Section of the Bridge Division 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.
- The Pavement Section of the Construction Division is responsible for technical support for pavement design such as falling weight deflectometer, ground penetrating radar, dynamic cone penetrometer, and seismic pavement testing.
- The district laboratory and Materials Section of the Construction Division are responsible for assisting with soils exploration and testing.
- A right of entry (see 2150: Obtain right of entry) or other written evidence of permission must be obtained before entering private property.
- Results may influence project design (e.g., high water table, hazardous materials).
Critical Sequencing.
- Perform hazardous materials investigations (see 3280: Perform hazardous materials survey assessment and investigation) before performing this task to avoid spreading contamination.
- Preliminary geotechnical surveys should be performed before developing a pavement design (see 2510: Prepare pavement design report) or establishing preliminary retaining and/or noise wall locations (see 2590 Establish preliminary retaining and/or noise: wall locations).
- Locate existing utilities before conducting subsurface exploration.
Resource Material.
- TxDOT Geotechnical Manual
- TxDOT Pavement Design Guide, Chapter 3, Section 2,Geotechnical Investigation for Pavement Structures
- U.S. Natural Resources Conservation Service (formerly Soil Conservation Service) Soil Survey by County.
2510: Prepare pavement design report
Description. The pavement structure represents one of the single most costly items on the typical highway improvement project. One important reason for doing a preliminary pavement design is to facilitate and enhance the accuracy of the cost estimate.
The preliminary pavement design is performed by a design engineer and requires the evaluation of various data to determine a proper pavement structure, including materials properties, environmental conditions, and cost. Traffic data (see 1430: Obtain Traffic Data) and geotechnical data (see 2505: Perform preliminary geotechnical surveys) 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 (including life-cycle costs and user-delay costs) and maximize the benefits.
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 the Construction Division.
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. All projects on the interstate highway system, and all projects on other facilities except preventive maintenance.
Responsible Party. Roadway design engineer or district pavement engineer
Sub-tasks.
- Collect necessary data, such
as the following:
- “as-built” construction plans; field evaluation data
- Existing and projected traffic data (see 1430: Obtain Traffic Data.) (request early in project development)
- Geotechnical investigation
- current pavement construction cost information
- drainage data
- historical performance information
- Pavement evaluation
- available funding.
- Contact district maintenance personnel for additional information on roadway pavement history.
- Check the Pavement Management Information System (PMIS) for historical data on pavement conditions. PMIS is available on the TxDOT mainframe computer system.
- Perform a condition survey - a site visit to assess pavement surface distress.
- Determine the requirements of the new pavement - what loads must it carry and how long before the first overlay is required.
- Determine the type of pavement to be built.
- Determine the different materials to be used for the different layers of the pavement structure.
- Determine the Performance Grade (PG) to be used for the Hot Mix asphalt layers.
- Determine the pay schedule to be used for evaluating the ride quality.
- Perform a life-cycle cost analysis as part of using automated design software (e.g., FPS19).
- Prepare the pavement design and develop a Pavement Design Report. (See the Pavement Design Guide, Chapter 2, Section 8, Pavement Design Report).
- 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.
- 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 2460, Update Cost Estimates).
Helpful Suggestions.
- Contact Transportation Planning and Programming Division for both existing and projected traffic data (see 1430: Obtain Traffic Data).
- The Materials and Pavement Section of the Construction Division is available for assistance as needed. Also, refer to the Pavement Design Guide.
- Contact the Materials and Pavement Section, 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.
- The district laboratory can run the triaxial test, Atterberg limits, and calculate potential vertical rise as part of the geotechnical investigation.
- 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.
- Soil types, weather conditions and material availability vary widely among districts. Consult with the district pavement engineer and construction engineers before starting a design.
- Pavement design must consider potential effects of groundwater on pavement performance along with other factors such as proposed roadway grades.
Critical Sequencing.
- Because one of the purposes of the pavement design is to estimate the cost of pavement related items, the pavement design should be performed before updating the cost estimate.
- This task should occur after collecting traffic and geotechnical data (see 2505: Perform preliminary geotechnical surveys) (including roadway pavement testing) and after setting preliminary grades.
Resource Material.
- TxDOT Pavement Design Guide
- AASHTO Design Procedures For New Pavements
- TxDOT Test Method Tex-117-E (Construction Division, Materials Section).
2520: 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 (See 2360: Develop typical sections) 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 (see 2510: Prepare pavement design report) is available at this time, it may be added to the typical section.
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. 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. TxDOT Roadway Design Manual, Chapter 2
Anchor: #i10213482530: Consider impacts on historic structures
Description. A mitigation plan (see the Environmental Manual) 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.
- Coordinate all development with the district environmental coordinator.
- Request that the landscape architect review the mitigation plan so that landscape and aesthetics are considered.
- 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 Requirements.
- National Historic Preservation Act of 1966
- Department of Transportation Act of 1966
- National Environmental Policy Act of 1969
- Historical and Archeological Data Preservation Act of 1974
- Intermodal Surface Transportation Efficiency Act of 1991.
Resource Material.
- TxDOT Bridge Project Development Manual and Historic Bridge Manual for information on historic bridges
- TxDOT Environmental Manual
- TxDOT Landscape and Aesthetics Design Manual, Chapter 3, Section 2, Prepare Mitigation Plan for Historic Structures (2530).
2540: Perform detailed Level of Service analysis
Description. Earlier in the process, a preliminary Level of Services (LOS) analysis of project alternatives (see 2310: Perform preliminary Level of Service (LOS) analysis) should have been performed to aid in selecting a preferred alternative.
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 2500: Develop preferred geometric alignment) and (see 2520: 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
Sub-tasks.
- Review traffic data obtained (see 1430: Obtain Traffic Data) on present and projected traffic volumes and other data such as percent trucks, design hourly volume, and the directional distribution.
- Obtain data on current and proposed roadway features (e.g., number of lanes, offset to obstructions, lane widths).
Helpful Suggestions. Several computer software programs are available to run the analysis.
Critical Sequencing. Perform as part of refining the preferred alignment and geometrics.
Resource Material.
- TxDOT Roadway Design Manual, Chapter 2, Section 2, Traffic Volume for LOS requirements
- Highway Capacity Manual by Transportation Research Board.
2550: 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.
Intelligent Transportation Systems (ITS) are an effort to improve safety and maximize operational efficiency of the transportation system by enabling TxDOT to detect incidents more quickly; provide information immediately to the public on incident location, its severity, effect on traffic flow and expected duration; and, change traffic controls to accommodate traffic flow changes due to the incident.
Pertinent Project Types. Mainly freeway/expressway and arterial highway projects; however, there are some rural applications.
Responsible Party. Roadway design engineer or traffic engineer
Sub-tasks.
- Obtain traffic data (see 1430: Obtain Traffic Data) and accident/crash data (see 2190: Obtain traffic accident data).
- Determine guide signs needed to increase roadway efficiency and safety.
- Consider including ITS strategies in the project.
Helpful Suggestions. Design guide signs to be legible to drivers approaching them and to allow adequate time for the driver to respond.
Critical Sequencing. Obtain traffic information (see 1430: Obtain Traffic Data) before performing this task.
Resource Material.
- TxDOT Contract Management Manual, Traffic Engineering Agreements
- Texas Manual on Uniform Traffic Control Devices.
2560: Submit requests for new or revised access points to interstate highways
Description. Regardless of funding or oversight, new or revised (e.g., ramp reversal or relocation) access points on interstate highways must be approved by the Federal Highway Administration (FHWA). The FHWA must ensure there is either no or only minimal adverse effect on the operation of the interstate facility.
A request for access modifications must be documented in an “Interchange Access Justification Report (IAJR).” 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. A checklist of information to include in this report is being added to the Roadway Design Manual, Chapter 1. A Level of Service analysis (see 2540: Perform detailed Level of Service analysis) will be required. Submission of the schematic layout is also generally required.
Pertinent Project Types. Projects involving new mainlane access points or revisions to existing access points on the interstate system.
Responsible Party. Project manager
Helpful Suggestions.
- Consider including a line diagram showing LOS results and traffic volumes.
- Informal coordination with FHWA during schematic preparation may streamline the FHWA review process later.
- Coordination and approval of the IAJR can take time since it must be approved by FHWA Headquarters staff in Washington, DC.
Critical Sequencing. This task should be done after preparing a schematic.
Authority Requirements. 23 USC §111
Resource Material. TxDOT Roadway Design Manual
Anchor: #i10216882570: Perform preliminary planning for weigh stations
Description. The need for new weigh/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 weigh/inspection stations. Construction of new weigh stations must be authorized by Texas Transportation Commission minute order. Projects that sever existing weigh stations should include construction of a replacement station as part of the project.
The need for a “weigh-in-motion” detector/station and its location is determined by the Transportation Planning and Programming Division of TxDOT. These stations are used to gather vehicle information - not for law enforcement.
Pertinent Project Types. Individual weigh/inspection station projects or highway improvement projects including weigh stations.
Responsible Party. Project manager
Sub-tasks.
- Obtain Commission authorization for any new weigh/inspection station construction.
- Contact the DPS to obtain details on weigh/inspection station design needs, consistent with Commission direction.
- Develop preliminary plans for the weigh/inspection station.
Helpful Suggestions. Clarify funding issues in question before beginning planning or design.
Critical Sequencing. If part of a larger project, perform this task when developing other preliminary plans.
Anchor: #i10217432580: Perform preliminary planning for bridges
Description. The location of proposed bridges must be determined early in project development. Preliminary planning (see the Bridge Project Development Manual) 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 Project Development Section of the Bridge Division processes the layout through the Railroad Section of the Traffic Operations Division.
Culverts with a total span greater than or equal to 20 ft (6.1m) 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
Sub-tasks.
- Identify applicable Federal Emergency Management Agency (FEMA), U.S. Corps of Engineer and U.S. Coast Guard constraints. (See 2340: Identify requirements for crossing navigable waters).
- Identify type, size, and locations of existing bridges.
- Determine vertical and horizontal clearance requirements.
- For bridge widening, determine load rating, and obtain condition survey (see Bridge Project Development Manual).
- Consider widening the existing structure versus replacement.
- Determine type, size, and location of proposed bridges.
- Review proposed bridge cross sections with local public agency when grade separation structures involve facilities not owned or maintained by TxDOT.
- Initiate geotechnical surveys (see 2505: Perform preliminary geotechnical surveys) for foundation design.
Helpful Suggestions. 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. 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.
- TxDOT Bridge Project Development Manual
- TxDOT Bridge Design Manual
- TxDOT Hydraulic Design Manual
- TxDOT Landscape and Aesthetics Design Manual, Chapter 3, Section 2, Perform Preliminary Planning for Bridges (2580).
2590: Establish preliminary retaining and/or noise wall locations
Description. Preliminary retaining and/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 2505: Perform preliminary geotechnical surveys).
The noise study (see 3330: Conduct noise analysis) 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 5640: Prepare retaining and/or noise wall layouts).
Pertinent Project Types. Projects having retaining and/or noise walls
Responsible Party. Roadway design engineer
Sub-tasks. The following sub-tasks are common to both retaining and noise walls:
- Determine if aesthetics is an important consideration because this will affect the type of design.
- Consider traffic control plan, soil considerations, and right of way limitations because these factors may dictate type of wall to be used.
- 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.).
- Determine right of way boundaries, and any additional site constraints.
- Coordinate with utility companies to determine any potential conflicts.
- Determine if street lights, overhead bridge signs, concrete traffic barriers, or traffic signs will be attached to the wall.
The following sub-tasks pertain to retaining walls:
- 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.
- On retaining wall layouts, include horizontal and vertical curvature information with stations and elevations along the top and bottom of the wall.
- Determine if the retaining wall also needs to act as a noise barrier wall.
- 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).
- Determine if the retaining wall will be supporting traffic lanes. If so, the design must account for traffic loading and barrier affect loading.
- Check sight distance for walls in cut sections - at intersecting streets and driveways.
- Submit retaining wall layout to Bridge Division if height will be greater than 25 feet (7.6 m).
The following sub-tasks pertain to noise walls:
- Coordinate with the environmental specialist to determine if a noise analysis and mitigation study is required. If so, determine if one was completed.
- Determine if a noise wall is the recommended mitigation measure for noise abatement. Refer to the project noise analysis and mitigation study report.
- 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 and/or noise walls
- 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.
- Provide adequate clear zone between travel lanes and the wall.
- 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.
- Create a smooth profile on the top of the wall for a pleasing appearance.
For noise walls
- Refer to the noise analysis for the location and dimensions of the proposed noise wall.
- 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.
- 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.
- 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.
- Use caution about building noise walls because they might limit future access to adjacent property.
Critical Sequencing.
- The noise study must be completed before performing this task.
- Preliminary retaining wall layouts should be submitted, when required, as soon as practical and before detailed design.
Authority Requirements.
Resource Material.
- TxDOT Roadway Design Manual for information on horizontal clearances, sight distance requirements, and other considerations for wall placement
- TxDOT Geotechnical Manual for information on retaining wall selection and design
- TxDOT Landscape and Aesthetics Design Manual, Chapter 3, Section 2, Establish Preliminary Retaining and/or Noise Wall Locations (2590)
- TxDOT Bridge Project Development Manual for information on submission requirements
- TxDOT Environmental Manual
- TxDOT Guidelines for Analysis and Abatement of Highway Traffic Noise
- Internet site - http://www.dot.state.tx.us/services/environmental_affairs/traffic_noise.htm
- TxDOT Intranet site- http://crossroads/org/env/Guidance/Traffic/default.htm.
2610: 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
Sub-tasks.
- Conduct a site investigation. (See the Hydraulic Design Manual).
- Identify potential outfall and stream crossing locations.
- Estimate the runoff (see the Hydraulic Design Manual) from the watershed.
- 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.
- Review U.S. Natural Resources conservation Service (NRCS)(formerly Soil Conservation Service) reports as well as USGS and FEMA flood maps.
- Verify past coordination with local governments having jurisdiction over the project area.
Helpful Suggestions.
- Consider the possibilities for future development in the area. Additional buildings and parking lots can change the rate and direction of runoff.
- Many cities maintain zoning and land use maps; these should be referenced when estimating watershed runoff.
Critical Sequencing. This task should be done after the preliminary roadway layout is determined.
Resource Material. TxDOT Hydraulic Design Manual
Anchor: #i10222202620: 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. (See the Hydraulic Design Manual).
The basic hydraulic design process begins with data collection (See the Hydraulic Design Manual). 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. The calculation process may be significantly easier with use of TxDOT-approved hydrologic and hydraulic computer software (see the Hydraulic Design Manual). 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. Preliminary hydraulic design can be performed after runoff is calculated.
Resource Material. TxDOT Hydraulic Design Manual
Anchor: #i10222782630: 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
Sub-tasks.
- Gather information on existing ROW, property lines, control of access, etc. (See 4000: Perform preliminary ROW research).
- Obtain project-specific minute order for controlled access facilities (see 1235: Obtain project specific minute order, if required).
- Develop plan to address identified encroachments.
Helpful Suggestions.
- Where possible and practical, consider reducing ROW acquisition costs by developing an alignment so that additional ROW is required from only one side of an existing facility; this will reduce the number individual parcels required.
- The proposed ROW should be sufficient for parallel drainage channels and cross-drainage structures.
- Identify needed drainage easements.
- The designer should strive to minimize displacements of homes or businesses while still meeting other design requirements.
- Intelligent Transportation System (ITS) infrastructure may affect ROW needs.
- If ROW is needed from any airport, contact the Planning Section of the Aviation Division for coordination.
- If existing features are determined to be an encroachment on State ROW, they will need to be removed.
- Reconfiguration of existing ramps may necessitate acquisition of additional control of access.
- Disposal of access rights must be handled according to 43 TAC §§ 21.101 – 21.106.
Critical Sequencing. This task should be performed concurrently with, or after, determining a preferred alignment and other geometrics. A ROW needs determination may play a key role in determining a preferred alignment because there may be existing ROW and access constraints - especially in urban areas.
Authority Requirements.
Resource Material.
- TxDOT Hydraulic Design Manual for information on drainage easements
- TxDOT Right of Way Collection
- TxDOT Access Management Manual.
2640: Identify existing utilities on geometric schematic
Description. The design engineer should obtain information on existing utilities (See 2180: obtain information on existing utilities) from utility owners and create a layout of the existing utilities.
Pertinent Project Types. All projects except preventive maintenance and restoration projects.
Responsible Party. Roadway design engineer
Sub-tasks.
- Coordinate with district utility coordinator.
- Collect utility information from utility owners.
- Develop a utility layout.
Helpful Suggestions.
- A utility layout may be more
easily prepared by performing the following steps:
- sending the schematic to utility owners who do not have utility plans readily available
- asking the owners to draw their utilities on the schematic - with distances referenced to the ROW or other reference points
- Consider using subsurface utility engineering (SUE). Information is available under Task 4200: Locate existing utilities.
Critical Sequencing. A utility layout should be created soon after developing the preliminary schematic.
Anchor: #i10224802650: 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 determines potential utility conflicts. Knowledge of these conflicts assists the utility owners in budgeting for anticipated adjustment costs.
Pertinent Project Types. All projects except preventive maintenance and restoration projects.
Responsible Party. Roadway design engineer
Sub-tasks.
- Review preliminary schematic with district utility coordinator.
- Locate utility conflicts in plan and profile.
- Contact the affected utility owners to discuss plans to address utility conflicts.
Helpful Suggestions.
- 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.
- 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.
Resource Material. TxDOT Utility Manual
Anchor: #i10225442660: Establish preliminary illumination locations
Description. There are two basic types of illumination systems 1) continuous illumination systems and 2) safety lighting systems. Illumination 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.
Pertinent Project Types. Projects requiring illumination.
Responsible Parties. Roadway design engineer
Sub-tasks.
- Discuss with area/district staff the need for agreements (maintenance and/or construction) with local entities.
- Determine if the lighting system meets warranting conditions and requirements contained in the TxDOT Highway Illumination Manual.
- Data to substantiate that warrants are met should be submitted with the request for programming and/or financing to the Design Division and should be shown on Form 1002.
- Determine the locations, mounting heights and offsets, and types of luminaires.
- Refer to FAA Circular 70/7460-1K to determine if FAA Form
7460-1 (available on the Federal Aviation Administration
website) is needed. A FAA form 7460-1 may be required if
the proposed illumination structures meet any of the following
criteria:
- taller than 200 feet (61 m)
- closer than 20,000 feet (6096 m) to an airport or seaplane base having a runway longer than 3,200 feet (975 m)
- closer than 10,000 feet (3048 m) to an airport or seaplane base having no runway longer than 3,200 feet (975 m)
- closer than 5,000 feet (1524 m) to a heliport.
Refer to the FAA website at www.oeaaa.faa.gov for more detailed information and to submit the proper form.
- Determine available power source locations from utility company.
- Develop plan sheets, pertinent notes, understructure lighting and details.
Helpful Suggestions.
- Lighting systems can be installed only on eligible roadways where the conditions warrant such installation.
- Intensity of illumination should be reviewed in residential areas to minimize impacts on residents.
- The power company can help locate power sources.
- The Traffic Engineering Section of the Traffic Operations Division is available to provide assistance, upon request.
Critical Sequencing. 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 Requirements.
- Federal Aviation Administration Form 7460-1 for specific requirements on construction near airports, heliports, and seaplane bases.
Resource Material.
- TxDOT Highway Illumination Manual
- AASHTO Roadway Lighting Design Guide
- NFPA 70: National Electric Code
- ANSI/IESNA RP-8, Roadway Lighting
- Federal Aviation Administration website at http://www.oeaaa.faa.gov, for forms and instructions
- TxDOT Standard Sheets: Roadway Illumination Details (RID); Roadway Illumination Poles(RIP); High Mast Illumination Details (HMID); Electrical Details (ED); High Mast Illumination Pole (HMIP); High Mast Illumination Foundation (HMIF).
2670: 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.
Pertinent Project Types. All projects except preventive maintenance and restoration projects.
Responsible Party. Roadway design engineer
Sub-tasks.
- Develop conceptual construction phasing plan.
- 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. Sequence of construction often affects selection of retaining/noise wall and bridge construction method. Future advancements in 3-D and 4-D design and modeling technology may help provide a view of how the project will look as it progresses through construction.
Resource Material.
- Texas Manual on Uniform Traffic Control Devices
- NCHRP Report 391: “Constructability Review Process for Transportation Facilities Workbook”, 1997, by the Transportation Research Board
2690: 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 first prepared during the Design Concept Conference. (See 2000: Conduct 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.
Pertinent Project Types. Projects for which a Design Summary Report was prepared.
Responsible Party. Project manager
Sub-tasks.
- Update DSR form completed during the Design Concept Conference.
- Revise project cost estimate (see 2460, Update Cost Estimates).
- Assess staffing needs for the next phase of work, detailed detailed design work (see Chapter 5, Section 2 Begin Detailed Design).
Resource Material. Design Summary Report (DSRform)