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Section 4: Policies, Standard Practices, Requirements, and Guidance

This manual identifies those policies, standard practices, criteria, guidance and references approved for use in carrying out the hydraulic design responsibilities in TxDOT. In this regard, the following definitions will be used:

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  • A policy is a statement of position, reflecting the preferred philosophy of the agency. Policy comprises a set of self-imposed boundaries on decisions in the course of business under ordinary or anticipated conditions.
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  • A standard is a fixed reference to guide the outcome and content (product) of the work. Standards are established where there is a consistent level of risk or there is a consistent technical or performance expectation for a specific product to work well in most cases. In this manual standards frequently refer to the expected design Annual Exceedance Probability (AEP) for a particular type of drainage structure on a particular class of highway. (See Chapter 4 for an explanation of AEP). Variances to TxDOT standards are not uncommon, but they need always be justified in writing. Attention to variances and guidance on how to request and justify them are included in this manual. Exceptions and waivers to the standards are handled in each section as applicable.
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  • Criteria are tests or indicators, in addition to standards, used to measure/judge achievement of applicable policy or standard objectives. Criteria may vary from project to project. An example of a criterion in this manual is the constraint on headwater depth at a culvert.
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  • TxDOT standard practices are methods and procedures that have a history of use within the department for addressing situations characteristic and commonly encountered. The only justification needed for the use of standard practices is evidence that they are appropriate for the situation at hand. Deviation from standard practices may be required in any situation where evidence that standard practices are applicable cannot be readily demonstrated.
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  • Guidance refers to recommended, but not necessarily required, actions to meet policies and standards, and expectations for applying discretion.
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  • Discretion in this context refers to engineering judgment applied by the practitioner to an appropriate technique or solution that is within an acceptable range of values.

In this manual, considerations for identifying appropriate standards, design criteria, and standard practices are included at the beginning of each chapter. Guidance is provided where appropriate to assist the user in formulating an approach to meet the standards and criteria.

Ignoring the appropriate standards and design criteria may result in a projeict delayed from the scheduled letting. If an exception is needed to a standard or design criterion, the TxDOT Project Development Process Manual (PDP) should be consulted for directions on applying for exceptions and waivers. Design Division Hydraulics Branch (DES-HYD) should be consulted as early as possible to work out an acceptable alternative.

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