When a TxDOT project with participation by the involves an encroachment on the 1% Annual Exceedance Probability (AEP) (100-yr event) floodplain, the location and design of the project must comply with FHWA Policy . Compliance with this regulation is required when a proposed project includes a new or expanded encroachment on a floodplain regulated by , or contains the potential for adversely impacting private property or insurable buildings on or near a floodplain.

The FHWA has prepared a non-regulatory supplement, , which explains the requirements for coordination with FEMA and the local community responsible for administering the NFIP under different floodplain encroachment scenarios. of this manual explains TxDOT procedures for compliance with these requirements.