The standards and methods in this manual are aimed at sound planning and design; they are guidelines rather than steadfast rules.

The design standards in this chapter represent minimums. Alternatives that meet a higher standard than presented herein

must be approved by the TxDOT District Hydraulics Engineer (DHE).

Exceptions to these design criteria may be allowed by TxDOT when they are in the best interest of the public and the alternative will be equivalent to the normally accepted method.

Errors in peak flow estimates, whether due to computational errors or errors in judgment, may result in a drainage structure that is either undersized, which could cause drainage problems, or oversized, which costs more than necessary. On the other hand, any hydrologic analysis is only an approximation. Although some hydrologic analysis is necessary for all highway drainage facilities, the extent of such studies should be commensurate with the hazards associated with the facilities and with other concerns, including engineering, economic, social, and environmental factors.

Design details are the responsibility of the design engineer and will be determined by good engineering practice.