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Section 2: Begin Detailed Design

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Overview

The design field survey, stream crossing hydraulics, and pavement design should be completed before detailed plan development. Traffic control and permits/agreements may delay the project if not handled properly at the beginning of detailed design.

This period of project development requires a substantial amount of the project manager’s experience and attention. Decisions made during this time will directly affect the project schedule and quality. Input from the project manager’s peers and supervisor should be sought for quality assurance of the project development process.

Design Division approval of geometric schematics for new location or added capacity projects should be obtained before beginning detailed design.

This section includes the following groups of tasks which may be performed concurrently:

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Traffic Control

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5040: Plan sequence of construction

Description. The designer must consider the construction sequencing, or staging, of the improvements to provide a design that is efficient to construct and maximizes mobility and safety during construction. Considerations include safety of the traveling public, TxDOT employees, and contractor employees.

The construction sequence must be detailed enough to identify the following:

  • additional needs for easements, rights of way, or railroad agreements
  • required modifications to final horizontal or vertical alignments – especially modifications needed for access to existing businesses and residences
  • additional environmental impacts due to construction (e.g., wetland impacts, hazardous material disturbance, or water quality impacts due to an intermediate construction phase)
  • previously unidentified project costs due to construction sequencing.

Safe, continuous operation by pedestrians and bicyclists should be considered in all stages of construction.

Reasonable access to all properties must be maintained during construction unless other arrangements are made with the property owners.

If an off-system roadway must be closed to traffic during construction, coordination with local entities is required. Road closure approval (see 5740: Obtain approval of road closure/detour plans) must be obtained.

In some cases, planning the sequence of construction may involve determining time of day limitations for construction activities to avoid impacts to traffic and adjacent properties.

Pertinent Project Types. All projects.

Responsible Party. Roadway design engineer

Sub-tasks.

  • Plan the sequence of construction with input from the area engineer, drainage, traffic and structural engineers, and construction inspection staff.
  • Obtain preliminary roadway and drainage plans. (See Preliminary Schematic).
  • Review construction year traffic data to evaluate lane closure impacts. Traffic data (see 1430: Obtain traffic data) should have been previously obtained.
  • Make a site visit to inspect existing conditions pertinent to sequence of construction (e.g., presence of fire stations, hospitals, or other facilities requiring uninterrupted access). This site visit (see 1010: Perform site visit) may supplement earlier site visits.
  • Determine the need for construction speed zoning and traffic control requirements at intersections.
  • Prepare preliminary staging plan using typical sections with plan views showing complex areas.
  • Coordinate plan with appropriate district and area office staff (construction, right of way, etc.).

Helpful Suggestions.

  • Make sure that non-typical and transition areas are detailed, because they are not represented in typical sections.
  • Consider the types of construction equipment that will be available or used, and ensure that the access and operational room needed for such equipment is provided.
  • Evaluate pavement design (see 2510: Prepare pavement design report) for compatibility with proposed construction sequence.

Critical Sequencing. Construction staging can have a direct impact on requirements for lengthy project activities such as right of way acquisition or environmental permitting. Consequently, the plan for construction sequencing should be developed as one of the first steps in detailed design.

Resource Material.

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5050: Develop conceptual detour/road closure plan

Description. Detours and road closures may be necessary to maintain traffic operations at acceptable levels of service during construction. Detours may include rerouting traffic to existing parallel routes, constructing temporary paved routes, or a combination of both. Effects on existing parallel routes and their capacity to handle additional traffic must be evaluated. Improvements to detour routes may be needed, such as pavement overlays, bridge widenings, bridge replacements, adjustments to signal timing or intersection improvements (for truck turning movements).

Consider the layout and operation of traffic control devices and drainage facilities for detours. Preparing final detour plans is described in 5730: Design detour roadways.

Pertinent Project Types. Projects requiring a plan to maintain traffic operations during construction.

Responsible Party. Roadway design engineer

Sub-tasks.

  • Obtain input from the area engineer, traffic and drainage engineers, and construction personnel.
  • Obtain preliminary roadway, drainage, and sequence of construction plans.
  • Obtain construction year traffic data for the project facility and potential parallel detour routes.
  • Consider the impacts to existing parallel facilities if capacity of the road being improved is substantially decreased during construction. Impacts to schools, emergency vehicles, pedestrians, bicyclists, and neighborhoods due to traffic rerouting should be considered.
  • Make a site visit (see 1010: Perform site visit) to inspect existing conditions including parallel routes.
  • Evaluate the condition of detour pavements and their ability to carry long term traffic.
  • If a roadway must be closed to traffic during construction, coordination with local entities is required and road closure approval (see 5740: Obtain approval of road closure/detour plans) must be obtained. If non-State owned roads are to be used as part of a detour plan, approval by the road owner (city, county, private) must be obtained. Coordinate with permit office and Motor Carrier Division if necessary.
  • Describe how access to all properties will be maintained during construction, unless other arrangements are made with property owners.
  • Coordinate detour plans with appropriate district and area office staff (roadway, drainage and traffic engineers, construction and right of way staff).
  • Submit District Engineer’s approval of road closure to the Design Division with submission of the PS&E.

Helpful Suggestions.

  • Detours should be designed to operate at least at the existing posted speed whenever possible. When this can not be accomplished, a construction speed zone request should be considered and the detour designed to meet the lowered construction speed limit.
  • Refer to information in 5720: Finalize sequence of construction, for details on items that will be required for the traffic control plan.
  • Consider safety lighting needs.

Critical Sequencing.

  • The detour plan should be developed as one of the first items in final design, along with the sequence of construction plan.
  • Coordination and preliminary approval of road closure/detour plans should be initiated when a road closure or detour is first considered.
  • Written approval of the road closure/detour plan should be obtained as soon as the detour plan is completed to the point that road closure/detour timing can be reasonably well defined and the plan has been approved by the district.

Resource Material.

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Permits and Agreements

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5080: Obtain miscellaneous permits

Description. Numerous state and federal agencies and others (“outside” TxDOT) regulate the impact of construction activities on their operations or environmental features. These entities have permitting requirements for this purpose.

Since approvals of impacts often require substantial completion of detailed plans, it is important to coordinate early with these entities. Some environmental permits (see 3110: Determine environmental permit requirements) may have been identified earlier as part of the environmental work on the project. These permits may not be received until environmental clearance is obtained but coordination should be well underway by this point in the project development process.

Refer to the list of potential environmental permits in the TxDOT Environmental Manual.

Refer to the list of miscellaneous permits in the PS&E Preparation Manual, Chapter 1, Section 2, Permits.

Pertinent Project Types. Projects having potential for impacting resources or entities, listed in permit tables cited above.

Responsible Party. Project manager

Sub-tasks.

  • Evaluate designs for impacts to resources and entities.
  • Investigate possible design modifications to reduce or eliminate impacts.
  • Discuss potential modifications and mitigation alternatives with area and district staff including the environmental coordinator
  • Review permit application requirements identified in Task 3110: determine environmental permit requirements.
  • Develop supporting data for permit application as required.
  • Prepare permit application and proposal for mitigation of impacts, if applicable.
  • Review permit application and mitigation proposal with area and district staff.
  • District environmental coordinator and/or Environmental Affairs Division staff submit permit applications to resource agencies.
  • Respond to agency requests for additional information.

Helpful Suggestions.

  • Resource agencies consider impact minimization or avoidance of utmost importance. Conduct a thorough analysis of preliminary engineering assumptions and conclusions regarding impacts. It is helpful to develop your own justification for impacts, especially if you did not perform the preliminary engineering.
  • It is recommended that you discuss assumptions and decisions made during preliminary design with appropriate team members.
  • Get familiar with recent permitting decisions made by resource agencies on similar projects. Obtain this information from the district environmental coordinator.
  • Agreements with railroad companies (see 2330: Initiate railroad coordination) are often difficult and time-consuming to obtain. These should be initiated as soon as possible.

Critical Sequencing. Obtaining permits can be a lengthy process and is often critical in the project development schedule. Coordination should begin as soon as the need is identified and should be followed throughout project development

Authority Requirements.

Resource Material.

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5100: Design environmental mitigation details

Description. Mitigation for impacts due to highway improvements, should be defined in project environmental documents, permit conditions, or agreements with regulatory or resource agencies. Mitigation measures are typically defined, without much detail, during advance planning. Mitigation plans should have been prepared in task 3390: Prepare environmental mitigation plans and in task 2530: Prepare mitigation plan for historic structures. Mitigation details to be implemented during construction must be delineated in plans and specifications.

Mitigation of environmental impacts due to the presence of hazardous materials may also be necessary. Mitigation measures typically include soil liners to contain hazardous materials, groundwater removal and treatment, and soil removal and disposal. Often, design modifications can be made to eliminate migration of underground contaminants and thereby eliminate the need for mitigation.

Mitigation details may include design drawing details showing special features such as protection of historic properties or mitigation of environmental concerns.

Off-site mitigation may justify separate construction contracts and schedules for this work. Developing regional mitigation alternatives may be desirable for TxDOT and regulatory agencies. The project manager should consult with the Director of Transportation Planning and Development and the Environmental Affairs Division at the start of detailed design.

Pertinent Project Types. Projects requiring mitigation of environmental impacts.

Responsible Party. Project manager

Sub-tasks.

  • Obtain input from the biologist, geotechnical engineer, landscape architect, and drainage engineer.
  • Obtain permits and agreements with resource agencies.
  • Explore possible regional alternatives and separate contracting on projects involving significant mitigation.
  • Coordinate mitigation measures with others (e.g., wetland creation/restoration or threatened/endangered species relocation with Environmental Affairs Division, or site acquisition with district right of way office).
  • Prepare mitigation plans.
  • Review and update the mitigation cost estimate (see 3390: Prepare environmental mitigation plans) as necessary.
  • Send plans to the district environmental coordinator to review for compliance with the environmental document.

Helpful Suggestions.

  • Mitigation may need to be completed before construction, and if mitigation requires the acquisition of property, acquisition of these parcels should be emphasized.
  • Obtain design input from related disciplines.
  • For mitigation requiring post-construction monitoring, have the technical expert develop a reporting process for monitoring. Monitoring may likely be long term, and a defined reporting process will ensure uniformity during this time.
  • Projects can be cleared environmentally and approved for letting only after addressing State Historic Preservation Office comments on historic structures.

Critical Sequencing. This task should be initiated subsequent to the field review. Timing of the completion of mitigation plans is project-specific and should be driven by the terms of agreement and permit requirements with resource agencies.

Resource Material.

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5110: Develop Environmental Permits, Issues and Commitments (EPIC) sheet

Description. The Environmental Permits, Issues and Commitments (EPIC) sheet is used to summarize the special requirements and restrictions related to the construction activity that has been permitted and the conditions of any permits. For example, it may depict areas to be avoided during construction due to the presence of endangered species, wetlands, etc.

A standard format is available for this sheet under the Roadway Standards grouping of Statewide TxDOT CAD Standard Plans Files.

Pertinent Project Types. All projects.

Responsible Party. Project manager.

Sub-tasks.

  • Review the environmental document and all permits and clearances to determine what requirements or restrictions apply to the project.
  • Download the latest EPIC standard sheet from the TxDOT website.
  • Ensure that areas to be avoided during construction due to endangered species, wetlands, or for other reasons are clearly identified on the EPIC sheet.
  • Ask the district environmental coordinator to review the draft EPIC sheet for compliance with the environmental document.

Helpful Suggestions.

  • Violating the condition of any permit may result in delay to the project. Be sure that all conditions are clearly outlined on the EPIC sheet.
  • The district Director of Transportation Planning and Development will need to certify in the Environmental Tracking System that the environmental commitments have been incorporated into the PS&E with the EPIC sheet.

Critical Sequencing. Timing of the completion of the EPIC sheet is project-specific and should be driven by the terms of agreement and permit requirements with resource agencies.

Resource Material.

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Design Data Collection

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5120: Review data collection needs

Description. Most field data collection will have occurred during preliminary design. However, as a large project develops, it is common for the designer to determine that existing data may be insufficient or need updating. Typically, some modifications to the original project concept occur as a project develops and conditions change. For example, if the development of the project has taken several years, traffic data and turning movements may need to be updated. Often, stream crossing hydraulics are not studied in detail during preliminary design.

Geotechnical investigations are necessary for the satisfactory long-term performance of structure foundations, retaining and noise walls, high embankments, pavement design, and stabilization of soft soils beneath pavements. If additional data is needed to complete the design of any of these features, it should be obtained at this time.

Previous data collection may include those described in the following tasks:

The project manager gathers and reviews all survey and geotechnical data collected, and reviews modifications to the project scope made since preliminary design. The project manager, in coordination with the roadway, structural and drainage engineers, determines the need for additional survey data. The project manager should contact the district pavement engineer, the district structural engineer (if one is available), and the Bridge Division, as necessary, to identify additional geotechnical survey needs.

Pertinent Project Types. All projects.

Responsible Party. Project manager

Sub-tasks.

  • Gather and review existing data.
  • Evaluate the project for changes (e.g., changed field conditions, project scope, environmental mitigation requirements, access revisions, or additional structures) made after original surveys and investigations.
  • Identify additional data required to finalize design.
  • Prepare work order for additional work.
  • Perform additional data collection and field and laboratory investigations.
  • Compile data and report results of investigations.

Helpful Suggestions.

  • Field conditions may change, and this can warrant additional data collection, especially in urban areas. Other issues, such as environmental mitigation, roadway access, retaining and noise wall locations, are often determined after performing initial field surveys. The project manager must determine if, and to what extent, these conditions necessitate additional data collection.
  • Geotechnical investigations may have been performed during the preliminary design phase. It is beneficial to discuss the extent and quality of this geotechnical data in the Design Conference (See 5020: Conduct Design Conference). Particular attention should be directed to high fills or deep cuts, highly expansive soils, the presence of groundwater, channel stability, and anticipated need for bridges, retaining walls, and noise walls. Investigations should include data for designing high-mast illumination, signal, and overhead sign structures.

Critical Sequencing. This task should occur as soon as possible after beginning detailed design.

Resource Material.

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Stream Crossing Hydraulics

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5140: Refine hydrologic study

Description. Hydrologic studies establish storm water flow rates, flow volumes, and locations of inflow and outflow to the highway facility for significant drainage areas. Recommendations from these studies can affect such major items as roadway alignments, bridge lengths, bridge foundations and channel design.

The hydrologic study is typically prepared during preliminary design as described in 2610: perform hydrologic study. At this stage, a refinement of the original study should be all that is needed. This refinement is usually needed to reflect detailed field survey data or a change in a basic design condition or assumption, or to reflect revised methodology if there is a significant delay between schematic development and PS&E development.

Pertinent Project Types. Projects involving a stream or floodplain crossings.

Responsible Party. Hydraulic engineer

Sub-tasks.

  • Identify any new, relevant data.
  • Verify validity of previous hydrologic study and determine if the study method used is still appropriate.
  • Evaluate any existing hydrologic data/results from previous studies (see 2610: perform hydrologic study) and update as appropriate or perform new hydrologic analysis for proposed hydraulic structure locations.
  • Based on the model, determine whether watershed revisions change stream water surface elevations.
  • Coordinate with the local FEMA floodplain administrator (FPA) for changes to water surface elevations and flood maps.

Helpful Suggestions. The Hydraulic Branch of the Roadway Design Section of the Design Division is available to provide assistance.

Critical Sequencing. This task should occur before 5150: prepare stream crossing hydraulics.

Resource Material. TxDOT Hydraulic Design Manual

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5150: Prepare stream crossing hydraulics

Description. Stream crossings at highways often involve a constricted flow opening. The designer establishes a design storm frequency and other criteria, and determines the size and type of opening. The design storm frequency is established considering factors such as functional classification of highway, size of the stream, or by performing a risk assessment. Other criteria include allowable velocities, allowable backwater/headwater, and Federal Emergency Management Agency/National Flood Insurance Program (FEMA and any other agency requirements.

The FHWA requires a bridge scour evaluation in the hydraulic design process for span bridges. The results of such an analysis may highlight the need for design adjustments such as increasing opening size, deeper foundations, pier and abutment protection, or other mitigation measures.

Pertinent Project Types. Projects involving a bridge, culvert, stream, or floodplain crossing.

Responsible Party. Hydraulic engineer

Sub-tasks.

  • Perform hydraulic analysis of existing conditions.
  • Review the results of FEMA or other studies (see 2200: Obtain hydraulic studies) performed during preliminary design preparation.
  • Identify whether the affected community participates in the FEMA National Flood Insurance Program (NFIP). If so, compliance with FEMA minimum criteria may be required.
    • Assess the accuracy of the FEMA hydrologic studies or computer model.
    • If appropriate, update the FEMA hydrologic model to reflect watershed revisions caused by proposed construction.
    • Hold preliminary coordination with the local FEMA floodplain administrator (FPA)or local government having flood control jurisdiction over the waterway.
  • Design improvements in coordination with the roadway design and structural engineers as applicable.
  • Perform hydraulic analysis of proposed structures, using the current effective FEMA model when available.
  • Perform scour evaluation and coordinate findings with structural and geotechnical engineers for proper foundation design.
  • Coordinate design recommendations with local FEMA floodplain administrator (FPA) or local government having jurisdiction.

Helpful Suggestions.

  • Assistance is available from the Hydraulic Branch of the Roadway Design Section of the Design Division.
  • Contact local FEMA floodplain administrator (FPA) early. The FPA can advise which base model to use and how much (if any) increase in backwater will be allowed. The FPA may also provide a copy of the original model or help locate one. It is advised to work closely with the FPA throughout the project.
  • The backwater profile program used in original development of the study may have been one of several types and from one of several sources. In Texas, the model most commonly used is the HEC-2 Water Surface Profile model from the Corps of Engineers. Typically, FEMA encourages that the model be updated to the most current acceptable model. If the stream was originally modeled using HEC-2, subsequent models should be done using HEC-RAS.
  • Floodplain encroachments must be explained in the environmental document.

Critical Sequencing.

  • Conduct water crossing hydraulic design along with final alignment design.
  • Hydraulic design may result in the need for drainage easements in areas not already owned or classified as waters of the State. In such instances, this task will have direct input into reviewing and obtaining additional ROW, access control, and easement requirements (see 5250: Review right of way requirements).

Resource Material. TxDOT Hydraulic Design Manual

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5160: Prepare hydraulic report

Description. For bridges, bridge-class culverts, or storm drains handling flows greater than 200 cfs (5.66 m3/s), the following must be sent to the Bridge Division for review and approval:

For projects with Federal oversight, the Bridge Division will send the layouts, sheets, and reports to the Federal Highway Administration (FHWA).

Information obtained during the 5140: Refine hydrologic study task is used in performing this task.

Pertinent Project Types. Projects having storm drains handling flows greater than 200 cfs (5.66 m3/s), bridges or bridge-class culverts.

Responsible Party. Project manager

Helpful Suggestions. Refer to the TxDOT Hydraulic Design Manual for documentation requirements.

Critical Sequencing.

  • Hydraulic calculation sheets and scour reports should be reviewed by the district and then submitted to the Bridge Division for review and approval before PS&E submission.
  • For bridge projects, send the following information with the bridge layout submission:
    • scour evaluation (do not send for bridge-class culverts)
    • hydraulic calculation sheets (send for bridges and bridge-class culverts).

Resource Material.

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