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Superseded on 10/7/2015 by Relationship between Design Speed and Posted Speed

Subject: Design Speed Date: Nov 4, 1988
From: /s/ Original signed by:
Director, Office of Engineering
Refer To: HNG-14
To: Regional Federal Highway Administrators
Direct Federal Program Administrator

Mr. E. Dean Carlson's April 15, 1985, memorandum, "Implementation of New Design Criteria for Federal-aid Projects," established the FHWA policy that for Federal-aid projects the selected design speed is to be equal to or exceed the posted or regulatory speed limit of the completed facility. Mr. Ronald E. Heinz's August 21, 1985, memorandum "Design Speed," provided guidance for applying that policy.

Since the issuance of the two memoranda, there has been considerable discussion of concerns over the application of that policy. These concerns have been primarily associated with, but not necessarily limited to, 3R projects and have focused on the perceived need for additional and unnecessary paperwork associated with justifying design exceptions.

Therefore, in order to clarify our position on this issue, and to emphasize the flexibility afforded by the provisions of the 23 CFR 625 and the actions taken to accept the Transportation Research Board (TRB) Special Report 214, Designing Safer Roads, Practices for Resurfacing, Restoration, and Rehabilitation, the following guidance is being provided for selecting appropriate design speeds for Federal-aid projects.

  1. For all nonfreeway 3R projects the design speed for specific elements may be determined and sel ected-as described in Technical Advisory (TA) T5040.28, "Developing Geometric Design Criteria and Processes for Nonfreeway RRR Projects", dated October 17, 1988. The TA provides for selecting a design speed that equals or exceeds the posted or regulatory speed limit or as an alternate, the use of specific, measured 85th percentile speeds for design of individual or series of horizontal and vertical curves as recommended in the TRB 3R study. The alternative procedure may be used whether or not the State has FHWA approved special 3R criteria.
  2. For all new and reconstruction projects,and all Interstate System projects, the geometric design should be consistent with speed implied to the driver by the posted or regulatory speed. Therefore, the design speed chosen for such projects should equal or exceed the posted or regulatory speed in order to assure that drivers operating at the legal speed limit can do so without unwittingly exceeding the safe design speed of the facility.

The intent of this policy is not to require speed limit posting or advisory speed signing to correspond to the actual design speed of the project or to an individual design element within a project. However, when the legal driving speed exceeds the design speed of a project element, the need for signs and markings should be based on recognized traffic engineering practice, accepted State policy, and be in accordance with the MUTCD.

/s/ original signed by
Thomas 0. Willett

Updated: 06/27/2017
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