State of California  Business, Transportation and Housing Agency

M e m o r a n d u m



Date : March 30, 2000

File: 608-309.2

 Subject: Vertical Clearances on the Rural and Single Interstate Routing System

This memorandum supersedes the August 20, 1993 memorandum on the 26,000 mile Priority Network (more recently termed the 42 000 km Priority Network). We are now issuing a revised map and table describing the limits of the new rural and single interstate routing system. The Department has received notification from the Federal Highway Administration (FHWA) that the previously established 42 000 km "Priority Network" is being eliminated, based on an agreement between the FHWA and the Military Traffic Management Command Transportation Engineering Agency (MTMCTEA). The new requirement is that all rural and "Single Routing Interstates" through urban areas will be required to meet the 4.9 m vertical clearance standard over the entire roadway width, including shoulders, as well as ramps and collector-distributor roadways. Exceptions to the 4.9 m vertical clearance standard will require approval by FHWA and the MTMCTEA. The Federal agencies plan to select a name for the revised system in the immediate future. Once a name has been selected, it will be included in an update to the Highway Design Manual.

In coordination with MTMCTEA, the FHWA has identified a subset of the Interstate System that would meet the most urgent national defense needs. FHWA has committed to the MTMCTEA that a 4.9 m minimum vertical clearance will be maintained where it already exists and clearances of less than 4.9 m will be upgraded as rapidly as practical. All projects on the rural and single interstate routing system will be closely scrutinized to ensure compliance with this vertical clearance standard. Exceptions to this standard, regardless of funding, whether for new construction, a project which creates a nonstandard situation, or for a project which does not provide for the correction of existing nonstandard vertical clearance (including 3R projects and CAPM), will be subject to Federal review.

Current Caltrans practice for projects on the Interstate System requires approval through the design exception fact sheet process for any proposed vertical clearance of less than 5.1 m for new construction or 4.9 m for overlay projects. Design exceptions for clearances of less than 4.9 m on the rural and single Interstate routing system must first receive internal review and approval within Caltrans. If the exception is approved by the Project Development Coordinator, the Project Engineer (PE) must submit the completed Design Exception Fact Sheet, with appropriate signature blocks, to the FHWA Division office. The transmittal must note whether or not the fact sheet addresses additional nonstandard design features on the proposed project. If the FHWA Division office approves of the exception to vertical clearance standards, FHWA will contact the MTMCTEA directly. The MTMCTEA has agreed to a maximum 10-day turnaround in review and response to a vertical clearance exception request. Due to this additional process, potential requests for design exception must be identified as early as possible and discussed with both the Project Development Coordinator, from the office of Design and Local Programs, and the FHWA.

For Interstate routes not on the rural and single Interstate routing system, the PE shall complete the Design Exception Fact sheet, submit to the Project Development Coordinator, and upon PDC approval, notify both the FHWA Division office and the MTMCTEA directly.

Wherever possible, vertical clearances should continue to be designed to comply with the Caltrans standards as described in the Highway Design Manual, Section 309.2. All exceptions to mandatory design standards (including the same vertical clearance) shall continue to require approval of a "Fact Sheet" as outlined in Section 82.2 of the Highway Design Manual (HDM), and as described in the Project Development Procedures Manual Chapter 21, format found in Appendix BB. Once the final approval is obtained, the Project Engineer shall send two copies of the approved Design Exception to Design and Local Programs and file the original in the project files.

Attached to this memo are two revised descriptions of the Interstate routes within California. One is a tabular description of the rural and single Interstate routing system, and the other is a map providing a quick general reference for both the rural and single Interstate routings and other Interstate routes. These descriptions will be included in the new HDM update as the revised HDM Table 309.2 and revised HDM Figure 309.2, respectively.

If you have any questions regarding this information, please contact either the Project Development coordinator or the Design Reviewer (formerly Geometric Reviewer) from the Office of Design and Local Programs assigned to your District.

Original signed by:
Program Manager
Design and Local Programs


Return to Design Memos Home Page