E 322 Clearances

Clearance is that distance by which a vehicle clears an object (such as other cars, hillsides, structures, walls, abutments, curbs, or pavements, etc.) or the clear space between them.

On projects involving structures and requiring structural design, the Bridge and Structural Design Division of the Bureau of Engineering concerns itself with the use of the State’s standards on clearances. The street project engineer is usually concerned only when realignment, widening, resurfacing, and/or grade changes are contemplated under or over existing structures.

Other areas in which the street designer is concerned are determination of clearances for sight distance, steep driveways, and turning radii in channelization or intersection projects. See Subsection E 321.5, Minimum Turning Radii.

Some of the methods used for checking clearances are included in this manual, such as design charts, tables, and formulas. Where they do not apply, it usually is necessary to resort to field measurements or to scaling of dimensions on plans, or the use of templates.

Two plastic vehicular templates are available in the pocket cover of this manual. These templates are used for determining the vertical clearance between the undercarriage of the vehicle and the critical pavement sections on steep streets and driveways. One template represents the composite shortest passenger vehicle; the other represents the composite longest passenger vehicle.

Both templates should be used in checking vertical clearances. For additional instructions on their use, see Subsection E 535.4, Design Check of Vehicular Vertical Clearance. For psychological as well as visual reasons, greater horizontal clearances are required between the vehicle and the obstruction on:

1. The vehicle’s right side than on the left side.
2. Underpasses than on overpasses.
3. Short-length than on long-length structures.

In addition, because of higher allowable speeds and larger volumes of truck traffic, greater horizontal clearances are required on major highways than on local streets.

E 322.1 State of California Standards

The following is taken from the State’s Planning Manual Part 7 – Design Structure Clearances (7-309). See Section E 020F(5b). Only the numbers referring to paragraphs in the State’s Manual have been changed to correspond to this Part of the Manual.

E 322.11 Through Roadbeds

These clearances are for through highways other than interchanges, grade separations, and miscellaneous structures.

E 322.111 Structure Clearances — State

The clearances given below constitute minimum standards.

1. Horizontal Clearances: In determining the horizontal clearance to bridge piers, abutments, sign structures, and light standards, measurements should be from the edge of the traveled way unless otherwise stated.  Additional horizontal clearance should be provided where necessary to meet sight-distance requirements.
   1. Two-lane State Highways: 10 feet on each side.
   2. Through Roadbed on Divided Highways and Freeway to Freeway Connections: The clearance to the left of traffic should be 6 feet on 4-lane and 6-lane designs and 9 feet on separated road- ways and on facilities with more than 6 lanes. On the right side, the clearance should be 11 feet.
   3. Single-lane Ramps: The clearances should be 4½ feet to the left and 9 feet to the right of traffic. If curbs are to be used, the clearance on the left is measured from the curb line; if there are no curbs, it is measured from the edge of the traveled way. On the right it is measured from the edge of the traveled way regardless of curbs.
   4. Two-lane Ramps, Speed-change Lanes, and Collector Roads: The clearances should be 4 ½ feet to the left and 9 feet to the right of traffic when there is a full shoulder.
   5. Other Roads and Frontage Roads: On all other roads, including frontage roads, the clearances to the lace of bridge piers, abutments, retaining walls, and other obstructions should be as follows:
      1. Two-way traffic: 6 feet on each side.

      2. One-way traffic: 4.5 feet on the left and 6 feet on the right in the direction of traffic.

         Where the provision is to be made for sidewalks, the pier, abutment, or wall should be placed at the edge of the sidewalk nearest the property line.

          

2. Vertical Clearances:
   1. Major Structures: The standard clearance should be 15 feet over the traveled way and 14 feet above the shoulders. The 14-foot clearance may be reduced over the top of curb or sidewalk area if the traveled way clearance requirements are also satisfied. A clearance of 16.5 feet is required on certain routes.
   2. Minor Structures: The vertical clearance for pedestrian overcrossings and other structures of a similar nature should be 17 feet over the traveled way and 16 feet above the shoulders. If a pedestrian structure is protected by a major structure, a clearance greater than that of the major structure need not be provided. The clearance for overhead sign structures should be 18 feet. These clearances should be measured in the same manner as for major structures.  When a vertical clearance of 16 ½ feet is provided over major structures, the requirements of Subsection E 322.112 (2) should apply.

E 322.112 Structure Clearances — Interstate

Except for the vertical clearances established below, the policy on structure clearances set forth under Subsection E 322.111 should apply to highways which are part of the National System of Interstate and Defense Highways.

1. Major Structures: The vertical clearance should be 16½ feet over the entire width of traveled way and shoulders of the through facility, speed-change lanes, ramps, and collector roads on all parts of the Interstate System classified as rural and on selected portions classified as urban.
2. Minor Structures: The vertical clearance for pedestrian overcrossings should be 18½ feet on portions of the highway system where the major structure clearance is 16½ feet. If such an over- crossing is protected by a major structure, a clearance greater than that of the major structure need not be provided.

The foregoing clearances should be measured in the same manner as for major structures. Where the 16-foot clearance is not provided for major structures, the clearances should conform to Subsection E 222.111 (2b). Sign structures should have a clearance of 18 feet.

3. Clearances for Frontage Roads: See Subsection E 222.111 (1e).

E 322.113 Tunnel Clearances

In one-way highway tunnels, the minimum side clearance from the edge of the traveled way should be 4.5 feet on the left and 6 feet on the right. For two-way tunnels, this clearance shall be 6 feet on each side.

The minimum vertical clearance should be 15 feet measured at any point over the traveled way and 14 feet above the gutter at the curb line.

E 322.114 Lateral Clearances for Elevated Structures

The minimum horizontal clearance between elevated highway structures, such as freeway viaducts and ramps, and adjoining buildings or other structures should be 15 feet for single-deck structures and 20 feet for double-deck structures. Spot encroachments on this clearance are permissible only with the advance approval of the State Division of Highways.

E 322.115 Structures Across or Adjacent to Railroads

Regulations governing clearances on railroads and street railroads with reference to side and overhead structures, parallel tracks, crossings of public roads, highways, and streets are established by the State Public Utilities Commission.

1. Normal Horizontal and Vertical Clearances: Although General Order No. 26-D specifies a minimum vertical clearance of 22½ feet above tracks on which freight cars not exceeding a height of 15½ feet are transported, a minimum of 23 feet is to be used in design to allow for ballasting and normal maintenance of track. See Subsection E 041.6 (10).

At underpasses, General Order No. 26-D establishes a minimum vertical clearance of 14 feet above any public road, highway, or street. However, the clearances specified under Subsection E 222.111 (2) should be used.

All curbs, including median curbs, should be designed with 10 feet or clearance from the track centerline measured normal thereto.

The principal clearances which affect the design of highway structures and curbs are summarized in Figures E 222.115A and B, below. It should be noted that collision walls may be required for the clearances given in Columns (3) and (4) of Figure E 222.115B, below. Usually, no collision walls are required if the clearance is 10 feet or more on tangent track and 11 feet or more on curved track.

2. Off-Track Maintenance Clearance: The 18- foot horizontal clearance is intended for sections of railroad where the railroad company is using or plans to use off-track maintenance equipment. This clearance is provided on one side of the railroad right of way.

On federal-aid projects, where site conditions are such that off-track maintenance clearance at an overpass is obtained at additional cost, federal- aid funds may be used for the costs of such overhead designs that provide up to 18 feet horizontal clearance on one side of the track. In such cases, the railroad is required to present a statement that off-track maintenance equipment is being used or is planned to be used along that section of the railroad right-of-way crossed by the overhead structure.

3. Over height Freight Car Clearance: On certain railroad lines described below, the Public Utilities Commission requires increased vertical clearance to allow for the operation of over height freight cars (more than 15 ½ feet high). The minimum clearance prescribed for these lines is shown in Figure E 222.115A, below. It should be noted that these certain railroad lines are subject to additions or deletions by the Public Utilities Commission from time to time.
4. Approval: All plans involving clearance from a railroad track should be submitted to the railroad for approval as to railroad interests. Such clearances are also subject to approval by the Public Utilities Commission.

To avoid delays, early consideration must be given to railroad problems when design is started on a project.

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E 322.12 Miscellaneous Roadbeds

These clearances are for roadbeds that are part of other than through structures, such as interchanges, grade separations, etc.