234.1 Access to Interstate Highways

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234.1 Interchange Justification for Interstate Highways.jpg

Interchanges are considered where conflicting high traffic volumes exceed those that can be handled efficiently and safely with at-grade intersections. They are also used to control access to the main highway. The location study for a proposed improvement recommends the type and location of a proposed interchange necessary to address these concerns. A precise analysis of traffic movement that justifies the necessity for an interchange is required. Depending on the complexity, appropriate modeling can include microsimulation or analysis using the Highway Capacity Manual. Access management guidelines are considered in analysis of operational and safety concerns.

MoDOT intends to provide access for all traffic movements at an interchange on the state highway system. In some cases, traffic volumes may not warrant the provision of ramps at the time of initial construction. However, right of way will be purchased to provide for the future ramps. The plans for initial construction of the interchange will show the location of future ramps for these traffic movements.

Justification for new or revised access to an interstate highway requires approval from FHWA. This approval is a two-step process that consists of concept approval and final approval. MoDOT requests concept approval from FHWA with an Access Justification Report (AJR). After concept approval has been obtained, final approval is automatic after the NEPA requirements have been fulfilled assuming no significant changes have been made to the original concept. This approval is necessary in order to receive federally controlled funding for the project(s) that will create the new or revised interstate access. Detailed guidance concerning the analysis and documentation necessary to justify a change in access to an interstate highway can be found on the FHWA Missouri Division website. Recent national policy guidance provides the following information:

  • Applicability: The policy is applicable to new or revised access points to existing interstate facilities regardless of the funding of the original construction or regardless of the funding for the new access points.
  • Access Point: Each entrance point to or exit point from the mainline, including a “locked gate” (for fire, medical or other emergency vehicles to reduce travel time or for maintenance activities or land access in remote locations), is considered to be an access point (e.g., a diamond interchange configuration has four access points).
  • Revised Access: A change in the interchange configuration even though the number of actual points of access may not change. This is subject to the complexity of the revision being made.

The intent of the national policy is to maintain an interstate highway at its highest level of service in terms of safety and mobility. With this in mind, each interstate access revision will need to be analyzed on a case-by-case basis to confirm that the safety and traffic operations of the interstate highway are not adversely affected.

Although not comprehensive, the following information identifies the major categories of projects that will or will not require an AJR.

234.1.1 Revisions Requiring FHWA Access Approval and an AJR

Concept approval by the FHWA Headquarters Office (Washington, D.C.) is required for the following types of interstate revised access:

  • A new freeway-to-freeway interchange.
  • Major modification of freeway-to-freeway interchange configuration (e.g., adding new ramp(s), abandoning or removing ramp(s), completing basic movements).
  • New partial interchange or new ramps to or from continuous frontage road that create a partial interchange.
  • New freeway-to-crossroad interchange located in a Transportation Management Area (TMA). A TMA is an urbanized area with a population of more than 200,000 people determined by the latest decennial census, or other area when the TMA designation is requested by the Governor and the MPO (or affected local officials), and officially designated by the administrators of FHWA and the Federal Transit Administration (FTA).

The FHWA Division Office (Jefferson City) can give concept approval for the following types of interstate revised access:

  • A new freeway-to-crossroad interchange not located in a TMA.
  • Modification of existing freeway-to-crossroad interchange configuration.
  • The completion of basic movements at a partial interchange.
  • Locked gate access.
  • The abandonment of ramps or interchanges.

Proposed shifts or breaks in the interstate access control lines may require an abbreviated AJR, depending on the extent of impacts resulting from the proposed revisions. At a minimum, access revisions that involve major traffic generators will be analyzed for traffic impacts to the interstate highway. The extent of the documentation will be consistent with the complexity and expected impact of the proposed access revision.

234.1.2 Revisions Not Requiring FHWA Access Approval

The following types of revisions to an interchange do not require FHWA approval:

  • The addition of left turn storage lanes, right turn storage lanes, and through travel lanes, traffic signalization improvements, or relocation or shifting the existing ramp termini at the crossroad.
  • Increasing the length of any deceleration or acceleration lanes on existing ramps. MoDOT will conduct an operational analysis and evaluation of spacing between interchanges to ensure safe weaving, diverging, merging maneuvers and good directional signing are provided.
  • Addition of continuous travel lanes to an existing ramp.
  • New signing, striping, and/or resurfacing of existing interstate ramps, where the geometric features are not changed.
  • Installation of roadside guardrail and concrete barriers (3R and safety projects).

All FHWA approvals for new or revised access are conditioned on MoDOT complying with all applicable federal regulations, including planning and right-of-way regulations and NEPA. FHWA approval constitutes a federal action that requires NEPA procedures to be followed. This even applies when changes to an interstate facility are not financed with federal funds. The earliest final approval can be given for an access request is after the completion of the NEPA process.