Bridges & Structures

Additional Guidance on 23 CFR 650A

Formerly Federal-aid Policy Guide Non-Regulatory Supplement NS 23 CFR, Part 650A,
September 30, 1992, Transmittal 5
See Order 1321.1C FHWA Directives Management

1. Storm Drainage Responsibility (23 CFR 650.115(a)). The analysis of design alternatives required by 23 CFR 650.115(a) for encroachments should include a determination of responsibility if a storm drain installation is proposed. The following guidance is separated by recommended responsible agency:
   1. State Highway Agency Responsibility
      1. Where facilities are in existence which convey storm water to the highway either by surface drainage or by existing storm drains, the highway agency is believed responsible for providing drainage on and across the right of way. The facilities for this drainage should avoid diversion and concentrations of water as much as possible.
      2. Drainage designs should be adequate and provide for increased runoff from developments within the drainage areas for 20 years hence.
   2. Municipality Responsibility
      1. If the municipality requests additional main drains or outlet sewers beyond the needs and responsibilities of the highway project, then the cost of providing this betterment should be borne by the municipality.
      2. In locations where municipalities wish to drain additional areas into the highway system to avoid constructing a separate system or for some other reason costs should be shared on an equitable basis. Such cooperative projects are believed desirable, but an agreement should be drawn upstating clearly the responsibilities if each agency involved.
         1. One method to prorate cost is in proportion to the storm water supplied to the proposed facility. This should be done using the same frequency of runoff for all areas considered, unless a control for regulating is possible.
         2. In cooperating with local municipalities, the highway agencies should guard against permitting overloading of the drainage system on or near the highway with the resulting hazard of damage by floods.
2. Cast-in-place Non-reinforced Concrete Pipe (23 CFR 650.115(a)).

   The analysis of design alternatives required by 23 CFR 650.115(a) for encroachments should not include consideration of non-reinforced cast-in-place pipe (CIPP) under the pavement or under high fills. Non-reinforced CIPP is considered acceptable on Federal-aid highway projects at locations such as storm drain and irrigation systems which are not subject to highway live loads or under high fills.

3. Design Standards for Flood Plain Encroachments (23 CFR 650.115(a)(1)).

   The intent of the statement, "as appropriate, a risk analysis or assessment," in section 23 CFR 650.115(a)(1) is to allow judgment as to the detail of design studies. Where site conditions or structural requirements substantially limit practicable design alternatives, the conventional hydraulic analysis coupled with a risk assessment should meet the requirements of the design standards. Where site conditions permit a range of design alternatives and flood losses are anticipated, an abbreviated or partial risk analysis may be appropriate. We would anticipate that use of the full scale detailed economic (risk) analysis as described in Hydraulic Engineering Circular number 17 would not be necessary for normal stream crossings, but would apply to unusual, complex or high cost encroachments involving flood losses.

4. Design Standards for Highways in National Flood Insurance Program Mapped Floodplains (23 CFR 650.115(a)(5))
   1. Federal-aid highway funds should not be used either (1) for payments to property owners or (2) for more costly highway facilities if, in either case, the costs are incurred to meet State standards that require less than 1-foot rise in water surface elevation of the 100-year flood. Exceptions for designs that limit the water surface to less than a foot may be granted on a case by case basis where the cost effectiveness of such designs can be demonstrated by an economic analysis.
   2. If it is cost effective to exceed the 1-foot increase, FHWA will participate in right-of-way costs for insurable buildings in order to limit flood damage increase for which the State or NFIP might be responsible. See Attachment 1 for options which should be considered if the 1-foot increase is to be exceeded.
   3. On April 21, 1992, the above policy was rescinded for all except Interstate completion and Interstate new construction and reconstruction projects. For all other projects, State highway agencies may use determined in accordance with their respective laws.
5. Procedures for Coordinating Highway Encroachments on Floodplains with the Federal Emergency Management Agency (FEMA) (23 CFR 650.115(a)(5).

   The procedures contained in Attachment 2 shall be followed to meet FHWA's responsibility to be consistent with the standards of the National Flood Insurance Program (NFIP) as set forth in 23 CFR 650, Subpart A, Location and Hydraulic Design of Encroachments on Flood Plains. The procedures establish some flexibility for achieving cost-effective encroachments on floodplains within communities that are in the NFIP. For all locations outside of NFIP communities or NFIP identified flood hazard areas, 23 CFR 650, Subpart A shall be followed for encroachment design.