State of California

Business, Transportation and Housing Agency

M e m o r a n d u m

To:	ALL HOLDERS OF THE 5TH EDITION OF THE HIGHWAY DESIGN MANUAL PROGRAM MANAGERS AND DIVISION CHIEFS FOR DESIGN , MAINTENANCE, TRAFFIC & CONSTRUCTION	Date :December 15, 1999 File: 608-309.2
From:	DEPARTMENT OF TRANSPORTATION DESIGN AND LOCAL PROGRAMS MAIL STATION 28
Subject:	Maintaining Vertical and Horizontal Clearances

With the recent attention focused upon the available clearance at structures, it is prudent that all designers take special care to ensure that their design complies with all vertical and horizontal clearance design standards, please refer to Topic 309 of the Highway Design Manual (HDM). Of particular concern is the vertical clearance remaining following an overlay. All projects, including new construction, RRR, and CAPM, must meet the appropriate minimum clearance design standard for the type of facility, as shown in Index 309.2 of the HDM, (for falsework, see Index 204.6). As always, it is the Engineer in Responsible Charge who must assure that all minimum design standards are either met or exceeded, or that any exceptions to the minimum standards are properly justified and documented, in accordance with Index 82.2 of the HDM.

In all cases, project managers should include the District Permit Engineer and the Regional Permit Manager in the decision to modify the vertical clearance of an existing structure, either permanently or temporarily. Efforts should be made to avoid decreasing the existing vertical clearance whenever possible, and consideration should be given to the feasibility of increasing the vertical clearance even where it currently exceeds our standards. The analysis should include consideration of other vertical clearances (existing and future) along the route, and available routing around any such reduced clearance structures.

Original signed by:
ROBERT L. BUCKLEY
Program Manager
Design and Local Programs

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