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Section 4: Preliminary Schematic

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Overview

Once data collection is substantially complete, the preliminary schematic activity phase begins. This section describes developing engineering solutions to satisfy the project need. Alternative alignments and typical sections are the major engineering variables set forth. An operational analysis is performed on alternatives to determine the Level of Service of each.

A geometric schematic (Refer to Chapter 2, Section 5) is required for new location or added capacity projects and for projects requiring control of access or an Environmental Impact Statement. A list of schematic requirements can be found in the TxDOT Roadway Design Manual, Chapter 1, Section 3. Schematics are also valuable to communicate design concepts to the parties involved in project development.

Landscape, aesthetic, bicyclist and pedestrian accommodation concepts are studied. Preliminary geotechnical surveys are conducted if important to the decision-making process. Preliminary pavement designs are developed so that project cost estimates can be updated.

Finally, after all alternative solutions are studied, they are compared, ranked, and a preferred alternative is selected.

For new location or added capacity projects, Design Division approval of the preliminary schematic may be requested at the district’s option before affording the opportunity for a public hearing. Design Division approval of the geometric schematic (see Chapter 2, Section 7) for these projects is required but may be obtained after environmental clearance.

Projects requiring control of access or an Environmental Impact Statement require Design Division approval of a geometric schematic before affording an opportunity for a public hearing. Check with the Design Division Field Coordination Section for exceptions to this requirement, particularly for rural projects with few abutting property owners.

A schematic may be developed for other projects as the district determines beneficial; Design Division approval is not required in these cases.

Decisions made in these tasks will be carried forward when developing the geometric schematic for the preferred alternative.

This section includes the following subsections and tasks, many of which may be performed concurrently:

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Alternative Selection

2300. Evaluate corridor alternatives

2310. Perform preliminary Level of Service analysis

2320. Evaluate route alternatives

2330. Initiate railroad coordination

2340. Identify requirements for crossing navigable waters

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Geometrics

2350. Evaluate geometric alternatives

2360. Develop typical sections

2370. Prepare Assessment of Landscape and Aesthetic Issues

2380. Develop bicyclist/pedestrian accommodation concept

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Update cost estimates

2460. Update cost estimates

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2300: Evaluate corridor alternatives

Description. A corridor is a broad band connection between two points and may encompass many potential routes. Preparing corridor alternatives during preliminary design involves developing many conceptual alternatives, including mode alternatives, that are feasible and reasonable in terms of construction, operation, and satisfying project goals. The end product is a single, preferred corridor and conceptual typical sections. This preferred corridor will be carried forward to the next stage, 2320: evaluating route alternatives.

Conceptual typical sections define basic elements including number and type of lanes (e.g., single versus high occupancy vehicle lanes), shoulders, type and range of median width, possible frontage roads, and range of offset to right of way limits. Details such as cross-slopes, side slopes, pavement structure, and station limits are typically not needed to define a particular concept. The number of lanes should be based on the capacity needed to operate at the desired Level of Service in the design year.

Although a more formal evaluation process will follow for selecting the preferred alternative, interim screening levels may be necessary to reduce the list of alternatives to a manageable number. Screening criteria should be based on characteristic elements that differentiate alternatives.

Pertinent Project Types. New location, added capacity, or controlled access projects or projects requiring an Environmental Impact Statement.

Responsible Party. Project manager

Sub-tasks.

  • Review projected design year traffic volumes. (See 1430: Obtain Traffic Data).
  • Verify that the facility type continues to remain appropriate.
  • Determine number of lanes.
  • Prepare conceptual typical sections.
  • Schedule public involvement activities such as public meetings. (See 2260: Conduct Public Meetings).
  • Select the preferred corridor.

Helpful Suggestions.

  • Obtain traffic data early. It may take three to four months to obtain design traffic data.
  • Early on, determine the availability and preference for base mapping such as aerial photos, USGS maps, topographic maps, or TxDOT county maps.
  • Thinking in terms of the end product for this task, determine when public input should be sought and what type of feedback should be requested.
  • Public involvement is a major factor in determining corridor alternatives. Present the development process and definition of alternatives in understandable terms for the public. Give careful consideration to the format used and level of detail presented to the public.
  • In describing alternatives, use names of intersecting roads or landmarks instead of stationing.
  • Establish a clear labeling or naming convention for alternatives.
  • Anticipate the need for creating options to an alternative and possible combinations of alternatives.
  • Some evaluation criteria may be less relevant than others in the decision making process. Therefore, it is important that each element is weighted if a matrix/numerical analysis is performed.
  • Keep alternatives basic in definition and avoid dwelling on details that are not significant at a conceptual level.
  • Prepare study area map after reviewing the TxDOT Environmental Manual, Chapter 2, Section 4, Define the Study Area.
  • Review topography and floodplain maps to estimate whether adverse hydraulic impacts can occur.

Critical Sequencing.

  • Request traffic data (e.g., traffic volumes) for use in defining typical sections early.
  • Through site visits or reviewing existing data, develop a clear understanding of the study area limits before developing alternatives.

Resource Material.

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2310: Perform preliminary Level of Service analysis

Description. A planning Level of Service (LOS) analysis uses preliminary traffic volume data for the design year and the implementation year. In some cases, additional analysis may be performed using data for the current year. After project alternatives are fully defined, including the “no-build” alternative, a planning LOS analysis can be conducted. Given a desired LOS for the design year, the typical number of lanes proposed is usually based on projected design year traffic volumes. As part of the evaluation process, the design year results can be used to compare alternatives to each other - and to the existing facility (as a baseline comparison) using current volumes. The results combined with cost estimates may also determine cost effectiveness.

Pertinent Project Types. New construction and reconstruction multi-lane highway and freeway projects.

Responsible Party. Roadway design engineer or traffic engineer

Sub-tasks.

  • Review existing and projected traffic data obtained (see 1430: Obtain Traffic Data) earlier.
  • Identify desired LOS for the design year.

Helpful Suggestions. Several computer software programs are available to run the analysis.

Resource Material.

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2320: Evaluate route alternatives

Description. A route alternative comparison is performed within the preferred corridor to identify the most feasible and reasonable route alternatives. The evaluation process developed for selecting alternatives is typically based on criteria addressing project objectives. Quality, organization, documentation, and presentation of data are critical to the success and credibility of the evaluation and selection process.

Pertinent Project Types. New location, added capacity, or controlled access projects or projects requiring an Environmental Impact Statement.

Responsible Party. Project manager

Sub-tasks.

  • Review traffic data (see 1430: Obtain traffic data) obtained earlier.
  • Select evaluation criteria and measures for comparing alternatives.
  • Evaluate each alternative.
  • Schedule public involvement activities such as ongoing stakeholder meetings (see 2110: Conduct early coordination with stakeholders and public meetings (see 2260: Conduct public meeting)
  • Identify the most feasible and reasonable alternatives.

Helpful Suggestions.

  • Obtain traffic data. It may take three to four months to obtain design traffic data.
  • Early on, determine the availability and preference for base mapping such as aerial photos, USGS maps, topographic maps, floodplain maps, or TxDOT county maps.
  • Determine when public input should be sought and what type of feedback should be requested.
  • In describing alternatives, use intersecting roads or landmarks instead of stationing.
  • Establish a clear labeling or naming convention for alternatives.
  • Anticipate the need for creating options to an alternative and possible combinations of alternatives.
  • Some evaluation criteria may be less relevant than others in the decision making process. Therefore, it is important that each element is weighted if a matrix/numerical analysis is performed.
  • Keep alternatives basic in definition and avoid dwelling on details that are not significant at a concept level.

Critical Sequencing. The most feasible and reasonable route alternatives must be selected before evaluating geometric alternatives.

Resource Material.

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2330: Initiate railroad coordination

Description. All work within railroad right of way (ROW) must be coordinated with the railroad owners. TxDOT may not perform work within railroad ROW without the proper agreement, liability insurance, and special provisions.

Approval for new, at-grade railroad crossings is difficult to obtain. Generally, an existing at-grade crossing in the general project area must be closed or grade-separated so no net increase in at-grade crossings results. TxDOT usually bears the burden of finding these “trade-off” crossings and negotiating with third parties if they are located off the State highway system.

Pertinent Project Types. Projects involving a highway-rail crossing, either at-grade or grade-separated, and all projects involving joint usage with the railroad (e.g., shared ditches).

Responsible Party. Project manager or roadway design engineer

Sub-tasks.

  • Coordinate with district railroad coordinator.
  • Locate all potential railroad crossings within project limits.
  • Determine existing crossing conditions and traffic control. Investigate the need for interconnection between various signals.
  • Identify opportunities to close or consolidate at-grade crossings.
  • Obtain a train crossing schedule from railroad owners. Inquire into major railroad line improvement plans. Obtain approval of clearances for grade-separated structures.
  • Develop recommendations for proposed rail-highway crossings.
  • Document all correspondence regarding the design of the railroad features.
  • Task 5360: Develop Exhibit A for railroad agreements. The Railroad Section of the Traffic Operations Division prepares and negotiates agreements with railroad owners.

Helpful Suggestions.

  • Consider installing new, and upgrading existing, railroad warning devices at railroad crossings within and near the project limits. Coordinate this with the railroad owner through the Traffic Operations Division. Railroad owners are responsible for maintaining railroad warning devices.
  • Consider interconnecting closely spaced, active railroad warning devices and highway traffic signals.
  • Consider replacing the crossing surface and subgrade. Both TxDOT and railroad owners have responsibilities for various work items. Identify and determine responsibilities for work on railroad ROW at this time.

Critical Sequencing. Initial railroad coordination should be conducted before selecting a preferred alternative because railroad issues may affect final alternative selection.

Authority Requirements.

  • Minute order 107279; 09/25/97; “Goals for the department's railroad safety program”
  • TxDOT memo; 01/13/97; “Railroad Agreements for Surface Treatment, ACP Overlay and Other Minor Projects on Railroad Right of Way”; from David Newbern; to all District Engineers
  • TxDOT memo; 07/29/94; “Railroad Agreements, Railroad Protective Liability Insurance, and PS&Es”; from Gary Trietsch and Robert Wilson; to all District Engineers.

Resource Material.

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2340: Identify requirements for crossing navigable waters

Description. The requirements for crossing navigable waters must be determined to ensure that projects are in compliance with federal regulations. All projects affecting a navigable waterway require coordination with the U.S. Coast Guard (

G) and the U.S. Corps of Engineers (COE). (See the Environmental Manual).

Pertinent Project Types. Projects affecting a navigable waterway

Sub-Tasks.

  • Determine if waterways are navigable.
  • Identify required permits.
  • Identify design criteria necessary to secure permits.

Responsible Party. District environmental coordinator

Helpful Suggestions.

  • For a proposed bridge crossing navigable waterways, lights and/or signals will likely be required which warn of bridge piers, caps, and beams, regardless of whether a
  • G clearance permit is required.
  • Assistance related to bridge requirements is available from the Project Development Section of the Bridge Division.

Critical Sequencing. When design criteria must be met to secure a permit, coordinate this early in schematic development.

Authority Requirements.

Resource Material.

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2350: Evaluate geometric alternatives

Description. Horizontal and vertical alignments are calculated for each reasonable and feasible route alternative and are shown on preliminary schematics. Normally this requires developing alignments for mainlanes, ramps, crossroads, and interchanges to ensure that design controls are satisfied. The end product is the selection of a preferred alternative.

Design the alignments to fit constraints that were identified earlier. The preliminary hydraulic design (See 2620: Perform preliminary hydraulic analysis/design) should be reviewed so the vertical “profile” alignment will accommodate drainage structures.

At this stage, alignments should be defined enough, geometrically, to determine basic requirements - such as required drainage structures, right of way (ROW), business/home relocations, and major utility conflicts. This information can be used in comparing alternatives, along with safety, environmental, travel efficiency and other considerations. Base maps do not need to be made from new field surveys or aerial photogrammetry. Such detailed data collection can be cost prohibitive for projects with several, long route alternatives. Base maps may include U.S. Geological Survey quadrangle (“quad”) maps, digital orthophotography maps, or older aerial photogrammetry maps. From these base maps, approximated existing ground profiles can be generated, proposed profiles can be developed, and rough cross sections can be generated. Horizontal alignments can be drawn to scale on the maps and then roughly computed. Later, a preferred geometric alignment will be selected, and a more detailed schematic may be prepared on survey controlled base mapping.

The preferred alignment and associated geometrics, including typical section(s), will be formally labeled as “preferred” and presented to the public. Reasons for establishing an alignment as preferred must be clear and should be recorded in project files for future reference.

A checklist of items to show on a schematic is available in the TxDOT Roadway Design Manual, Chapter 1, Section 3.

A preliminary schematic will accomplish the following goals:

  • Formulate design concepts for the project.
  • Present design elements collected in one graphic document - drainage structures, basic traffic data, project constraints, typical sections, etc.
  • Serve as a basis for approval-agreement on scope, design, etc., between districts, divisions, FHWA, counties, cities, and railroads - as applicable.
  • Establish relationships between the project and environment.
  • Define ROW and access control requirements.
  • Act as a public information communication tool. For better public understanding of a project, a schematic may be supplemented by a physical scale-model or computer visualization. These may be needed for very costly, controversial projects or complex projects such as interchanges.
  • Serve as the guide for detailed design and plan preparation.

Pertinent Project Types. New location, added capacity, or controlled access projects or projects requiring an Environmental Impact Statement.

Responsible Party. Roadway design engineer

Sub-tasks.

  • Review design traffic data (see 1430: Obtain Traffic Data) obtained earlier. Traffic data such as current and design year ADT volumes may be shown on the schematic.
  • Prepare a base map for the schematic's plan view showing existing topographic features. Base map is not necessarily from detailed field survey data or aerial photogrammetry; it may be from USGS quad maps or digital orthophotography.
  • For schematics in CADD, follow TxDOT's standards for CADD drawing levels in the PS&E Manual, Chapter 2, Section 4; this will provide easy transition to preparing PS&E plan sheets from schematics.
  • Add existing ROW limits (see 4000: Perform preliminary right of way research), locations of major utilities, etc.
  • Add constraints (e.g., proximity to historic structure, hazardous/petroleum materials, threatened/endangered species, wetlands, or noise attenuation); add labels or dimensions if appropriate.
  • Show how constraints will be handled.
  • Task 2360: Develop typical sections and add to schematic.
  • Establish computed horizontal alignments and add to schematic.
  • Evaluate need to realign heavily skewed intersections.
  • Establish sizes of drainage structures, and add location and size data to schematic. Only major-cost structures are needed for preliminary schematics.
  • Establish computed vertical alignments and add to schematic; adjust horizontal and vertical alignments as needed.
  • Generate preliminary cross sections to aid in determining right of way (ROW) needs and earthwork volumes.
  • Determine ROW needs and control of access restrictions (see 2630: Determine right of way and access needs), and add limits to schematic. Examine ROW needs for special drainage or run-off pollution control measures (e.g., detention or filtration basins). Obtain project-specific minute order for controlled access facilities (see 1235: Obtain project specific minute order, if required).
  • Consider significant utility conflicts. Add labels, identifying potential conflicts, to schematic.
  • Consider traffic handling during construction; this should be a major consideration.
  • Evaluate pavement design type (see 2510: Prepare pavement design report) for compatibility with proposed construction sequence.
  • Coordinate landscape and aesthetic considerations with landscape architect.
  • Consider hydraulic issues such as backwater flooding and scour/erosion potential.
  • Identify needed design exceptions or waivers (see 2870: Submit design exceptions/waivers for approval). Alignment and other geometric features must meet TxDOT's minimum design standards; otherwise a design exception or waiver is required.
  • If any improvements are planned involving railroad ROW, the district railroad coordinator should contact the Railroad Section of the Traffic Operations Division for early coordination with the appropriate railroad company (see 2330: Initiate railroad coordination).
  • Schedule public involvement activities such as ongoing stakeholder meetings (see 2110: Conduct early coordination with stakeholders) and public meetings (see 2260: Conduct public meeting).
  • Select preferred alternative.

Helpful Suggestions.

  • For schematics in CADD, consider plotting a separate, easy-to-understand schematic for public view using CADD capabilities. Make the schematic as uncluttered as possible; keep stationing because it is useful while taking notes with the public.
  • The CADD schematic is typically plotted in a continuous roll for viewing the entire project; however, it may be cut into sheets if needed. Sometimes separate sheets may be needed to show enlarged areas of a project having large amounts of detail.

Resource Material. The following table indicates where more information related to the evaluation of geometric alternatives may be found:

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For information on

Refer to

Roadway design criteria

TxDOT Roadway Design Manual

Schematic checklist

TxDOT Roadway Design Manual, Chapter 1, Section 3

Bridge planning

TxDOT Bridge Project Development Manual

Bridge design

TxDOT Bridge Design Manual - LRFD

Landscape and aesthetics

TxDOT Landscape and Aesthetics Design Manual, Chapter 3, Section 2, Evaluate Geometric Alternatives (2350)

Hydraulics

TxDOT Hydraulic Design Manual

Bike lane/bike trail design criteria

AASHTO Guide for the Development of Bicycle Facilities

Pedestrian Accommodation

AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities

Quantitative safety evaluation

Tools developed under TxDOT research project 0-4703, “Incorporating Safety into the Highway Design Process.” Tools and reports are available at http://d2dtl5nnlpfr0r.cloudfront.net/tti.tamu.edu/documents/5-4703-01-1.pdf.



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2360: Develop typical sections

Description. Typical sections are developed as part of selecting design alternatives. The typical section geometry should include the following information:

  • existing and proposed right of width,
  • pavement cross slopes,
  • lane, shoulder, and median widths,
  • side-slope rates for both cuts and fills for all proposed highway mainlanes, ramps, frontage roads, and cross roads,
  • clear zone widths,
  • provisions for landscaping and aesthetics,
  • noise attenuation devices, and
  • roadway elevations relative to local floodplain.

Design criteria for features shown on typical sections can be found in TxDOT's Roadway Design Manual, Chapter 2. If pavement design information (see 2510: Prepare pavement design report) is available at this time, it may be shown on the typical section.

Pertinent Project Types. All projects

Responsible Party. Roadway design engineer

Resource Material.

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2370: Prepare Assessment of Landscape and Aesthetic Issues

Description. The assessment of landscape and aesthetic issues identifies the issues that will affect the physical design form and detail of the project. A landscape architect should be consulted to prepare an Assessment of Landscape and Aesthetic Issues (ALAI). (See the Landscape and Aesthetics Design Manual, Chapter 3, Section 2, Prepare Assessment of Landscape and Aesthetic Issues ( 2370). After the project progresses and concepts are refined, recommendations may include any of the following:

  • aesthetic improvements by any of the following:
    • adjustments to the vertical or horizontal alignment or median width
    • use of aesthetic construction materials (having color and texture)
    • use of vegetation
    • use of lighting
    • aesthetic design of structural components
  • erosion control (temporary for construction and permanent)
  • environmental mitigation (e.g., restoration of vegetation lost through construction, sound barrier wall).

The district or division landscape architect can assist in providing guidance upon request.

Pertinent Project Types. New construction and reconstruction projects.

Responsible Party. Roadway design engineer

Sub-tasks.

  • Coordinate landscape/aesthetics plan with district or Design Division landscape architect.
  • Obtain data on existing conditions from soil surveys and topographic surveys.
  • Prepare concept proposal including data such as construction and maintenance costs.
  • Consider environmental justice issues if unusual or high-cost amenities are proposed that vary from usual TxDOT practice.

Authority Requirements.

Resource Material. TxDOT Landscape and Aesthetics Design Manual, Chapter 3, Section 2, Prepare Assessment of Landscape and Aesthetic Issues (2370)

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2380: Develop bicyclist/pedestrian accommodation concept

Description. Accommodations for bicyclists and pedestrians should be considered on all roadway projects. If accommodations are to be provided, preliminary plans should be developed for the bicyclist/pedestrian accommodations.

Pertinent Project Types. All projects

Responsible Party. Roadway design engineer

Sub-tasks.

  • Decide what accommodation type, if any, can be reasonably provided.
  • Provide a reasonable alternative route if an existing bicyclist/pedestrian facility is being affected by proposed construction.
  • Coordinate with public transportation providers to facilitate provision of intermodal connections.

Helpful Suggestions.

  • Refer to local bicyclist/pedestrian plans, if applicable.
  • Coordination with the district bicycle coordinator and district pedestrian coordinator. Coordination is essential during the planning stage.
  • Where new bicyclist/pedestrian facilities are proposed, include sufficient information to explain the reasons for facility selection in the environmental effects statement.

Critical Sequencing. Include provisions for bicyclist/pedestrian accommodations in the preliminary schematic.

Authority Requirements. 23 CFR Part 652

Resource Material.

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2460: Update cost estimates

Description. Construction and right of way cost estimates, and corresponding DCIS data, should be updated periodically to reflect project changes. Any cost overruns will affect district programming of projects and should be identified as early as possible. For more information, see 1200: Prepare cost estimate. The cost estimates should accurately identify approved funding sources (federal, state, and local participation.)

Eligible utility adjustment costs must be included in the right of way cost estimate.

Pertinent Project Types. All projects

Responsible Party. Roadway design engineer

Helpful Suggestions.

  • When recalculating the cost estimate, be sure to use current unit bid prices.
  • Consider factors such as the following:
    • geographic location (i.e., remoteness) and proximity to material sources
    • recent bid prices on similar projects
    • anticipated difficulty of construction
    • presence of restricted work areas or schedules
    • project size relative to previous project sizes
    • proposed project schedule
    • expected construction staging
  • If VE requirements are met, conduct study.
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