Preliminary Engineering Design for Construction
In general, the following elements should be completed during the schematic layout portion of preliminary design for transportation projects on the state highway system:
- Preliminary geometric alignment
- Typical sections
- Pavement designs
- Bridge layouts
The TxDOT district may define what elements are necessary for schematic design review for transportation projects not on the state highway system and other linear projects. Specialty projects such as buildings may involve scaled plan views, elevations, typical wall details and floor plans.
The local government must develop projects using design criteria in the TxDOT Roadway Design Manual for all roadway projects with state or federal funds and all projects on the state highway system regardless of funding source. Functional classification must be based on the TxDOT Functional Classification map.
The local government may select design criteria in accordance with its own practice for highway projects off the state system with no state or federal funds and non-highway projects off the state system that may include state or federal funds. Use of recognized design criteria from industry groups such as AASHTO is recommended.
If the local government does not use TxDOT-approved guidelines, the local government’s guidelines must be submitted to TxDOT for review and approval. This approval should be secured early in the project development process to avoid significant changes.
All reasonable effort must be made to produce a project that meets the established design criteria. However, there may be occasions when one or more design elements do not meet requirements. Exceptions, waivers or variances may be granted as an engineering decision if properly documented and supported.
Design Level of Service
Level of service (LOS) is a measure of traffic flow and congestion. A planning LOS analysis involves little detail and is used for preliminary facility sizing. Selecting a design LOS is a conscientious attempt to reasonably accommodate traffic in the design year.
A geometric schematic shows features such as:
- Location of interchanges
- Number and arrangement of lanes
Access management must be considered during the design of transportation projects on state and federal highway systems.
Value engineering is the systematic application of recognized techniques that:
- Identify the function of a product or service
- Establish a value for that function
- Provide the necessary function reliability at the least overall cost
Value engineering studies are required on federally funded projects on the federal-aid system with an estimated cost over $50 million and bridge projects with an estimated cost over $40 million. The value engineer study requirement must be fulfilled before construction is authorized.
Right of Way, Utility and Railroad Coordination
Right-of-way acquisition, railroad coordination and utility relocations are identified during the preliminary design of construction projects. Ideally, these tasks are completed before construction begins.