Driveways should be designed to minimize possible conflicts between the users of parking facilities and all users and modes of the abutting street system. The design should address pedestrian safety, sight distance, lane dimensions of the curb lane (i.e., a narrow curb lane may require a wider driveway), size and turning characteristics of vehicles using the driveway, (i.e. delivery trucks require wider driveways), complexity of vehicular movements, density of traffic on the abutting street, speed of vehicles on the abutting street, arrival or departure rate of vehicles using the driveway, and any other considerations that would affect the safety and efficient use of City streets. It should be recognized that driveway design recommendations may vary depending upon site constraints, location, and usage.
The street designer is usually required to design only that portion of the driveway lying between the curb and the property line. However, occasionally driveways located on private property may also have to be designed. This may require meeting certain Department of Building and Safety driveway requirements and other design considerations. See Section E 535.3, . In addition, the problems encountered may differ for driveway design on fully improved streets as opposed to partially improved or unimproved streets. Standard driveway design as well as design under unique conditions will be covered below with additional recommendations provided in the Driveway, Access, and Circulation Design Guidelines prepared by the City of Los Angeles Department of Transportation (LADOT).
E 535.1 On Improved Streets
An improved street usually has an officially established street grade. Using this established grade, the longitudinal and transverse driveway grades are determined. The transverse driveway grade is usually laid parallel to, and in the same vertical plane as, the longitudinal street curb grade. The curb is then depressed, and a longitudinal driveway grade is designed to connect the top of the depressed curb to the property line. The various driveway components that may require design include the depressed curb, the side slopes or curb returns, the Y slope, and the sidewalk area of the apron.
E 535.11 Depressed Curbs
The treatment of existing and proposed depressed curbs depends on the property owner’s intent and continued use of the driveway. The extent to which the existing or proposed street has been or will be improved may also affect the depressed curb design details.
E 535.111 Existing
Driveways or depressed curbs which have been abandoned should be removed. The depressed curb should then be replaced with full-height curb (prevailing curb height). The border portion should be completed to conform to the City’s border requirements. See Section E 650, Borders. The sidewalk area of the apron may be left in place if it is in satisfactory condition.
If a portion of the driveway has been previously constructed and meets the City’s standards as to grade, condition, and thickness (a minimum of 3 inches thick for existing residential driveways), a change of curb grade requires a new Y slope to be constructed. Under these conditions, the remaining portions of the driveway may remain in place and be joined by the new driveway Y slope. If an existing driveway is to remain in use and the depressed curb does not conform to the latest Standard Plans, the nonconforming depressed curb should be removed before a new Y slope is constructed. The new depressed curb and Y slope should then be constructed monolithically, as indicated in Subsection E 535.112, below.
E 535.112 Proposed
The proposed depressed portion of the curb (lip) is constructed 1 inch above the existing flow line of the concrete pavement or gutter. Where the prevailing curb face in the vicinity of the driveway is 6 inches or less, and if the pavement adjacent to the curb is bituminous material, the depression may be constructed flush with the pavement (0-inch lip). If the prevailing curb lane is higher than 6 inches, a 0-inch curb face may result in too steep a slope for the driveway apron.
It may be necessary to provide better vertical clearance due to the scraping of the vehicle’s underparts on high roadway crowns, steep driveways, abrupt grade breaks, etc. If the adjustment of these factors appears unfeasible, a maximum of a 2-inch-high lip may be used if it will help correct the vertical clearance impairment.
E 535.12 “Y” Slope of Driveway Apron
The design standards used for the Y slope construction are based on Driveways Standard Plan (S-440-4). As the table on Figure E 630A (1) indicates, the horizontal length of the apron to be used is dependent on the existing or proposed curb face. Where the length of apron used will result in the top of the Y slope extending into the sidewalk area, a Case 2 or Case 4 driveway should be used.
These figures are based on standard streets with standard borders (distance between curb and property line). However, on some streets, particularly hillsides, there may be only a substandard width border available or some other peculiar existing condition. This may require the use of some combination of curb face and Y slope, as indicated on the table of Figure E 635.12. In any case, the combination used should not result in a percentage slope of the apron below the heavy line shown on the chart. If these values are exceeded, the vehicle’s vertical clearance must be checked by use of the templates, as discussed in Section E 535.4.
E 535.13 Sidewalk Area of Apron
The driveway grade should be set extending upward from the top of the Y slope at the rate of 2 ½ percent. See the sketch on Figure E 635.12. However, in certain situations some latitude in driveways slope is required to meet existing improvements or to improve the impaired vertical clearance of a vehicle traversing the driveway. The driveway slope may vary upward from the top of the Y slope to the property line, from a minimum of 1 percent to a maximum of 6 percent.
E 535.2 On Unimproved or Partially Improved Streets
Driveways may be constructed on streets that are unimproved or partially improved but may be subject to certain conditions as described below.
E 535.21 Where a Street Grade Has Been Previously Established
The unimproved or partially improved streets may have existing abutting property which is undeveloped or partially or fully developed. It may be found that where the street grades have been established in prior years, little or no regard was given to these grades when some or most of the abutting property was developed. Or another situation may be found where the existing improvements have been constructed to the established grade, but a construction problem exists at a particular proposed driveway location.
E 535.211 Driveway Construction to Meet Established Street Grade
Where little or no improvement has been made to abutting property, a property owner must construct the driveway to the established street grade. In hillside streets at the site of the proposed driveway, the existing terrain may be considerably above or below the established grade.
A transitional grading section must be provided between the proposed grade of the driveway and the existing street grade on either or both sides of the driveway. This transition section must provide a smooth grade, adequate sight distance, and good drainage. Under these circumstances the driveway construction may create grading and drainage problems, as discussed below.
- Grading — The transition grading may require the raising or lowering of existing garage floors, the remodeling or redesigning of existing buildings or buildings being designed, or the construction or reconstruction of sidewalks, walls, driveways, etc., on private property.
Due to the varied nature of the problems encountered in this regard, reference is made to other Parts of the Manual and other Chapters, Sections, or Subsections of this Part of the Manual. It is further urged that the street designer consult with other offices. For example:
- Storm Drain Design Division or the Storm Drain Section of the District — On drainage.
- Bureau of Standards — On slopes.
- Bridge and Structural Design Division or the Department of Building and Safety — On structures.
- Street Opening and Widening Division or the Bureau of Right of Way and Land — On right of way.
- City Attorney – On legal matters.
- Other involved entities – On their specialties.
2. Drainage — Drainage problems may develop because of extensive grading, by erosion, or by the creation of a sump.
- Erosion control — Street runoff from a small residential lot may be considered a negligible drainage factor. However, the roof, parking area, and other impervious surfaces of the lot may drain toward the street. When the driveway is constructed to concentrate and channelize the flow of water to the unimproved street, some form of drainage control must be included with the driveway construction. Driveways should not normally be designed nor permits automatically issued for this drainage situation. However, it may be determined by field inspection or design study that the driveway pavement will eliminate poor drainage conditions, such as local water pockets in a graded gutter, and will not worsen the drainage situation. If this is the case, the driveway construction should be permitted.
- Sump elimination — The elimination or accumulated water where a sump may be created occurs when the driveway construction and the accompanying grading result in the formation of a sump in the street or the blocking of drainage from abutting property.
When the street is unimproved and the development is limited to only one or two properties, the costs incurred by one owner due to drainage and construction problems may be prohibitive. This may prevent property development until such a time as the entire street is improved and the costs shared by all or most of the property owners.
E 535.212 Driveway Construction Not to Meet Established Street Grade
Where most of the property has been developed, it may be extremely costly to require all of the property owners to build or rebuild the driveways and possibly garages, walls, sidewalks, etc., to the established street grade. In this case it may be found expedient to reestablish the street grade to meet the existing improvements. The proposed roadway and the proposed driveways would then be constructed to the new grade. However, before attempting to redesign the established street grade, the Division or District Engineer or his assistant should be consulted.
E 535.22 Where No Street Grade Has Been Previously Established
A grade should be determined for the entire street where no street grades have been previously established. The design criteria as outlined by this Part of the Manual should be used. The driveway grade is then superimposed on the proposed street grade profile. Adjustments should be made to the proposed street grade at the proposed driveway site to minimize the cost of the driveway construction. However, this adjustment should be made without sacrificing the City’s design standards or policies and should not be made at the expense of the existing or future development of abutting properties.
E 535.23 Streets With Curb Only (Roadway Not Paved)
At locations where curb has been or will be constructed and where there is no existing or proposed roadway pavement, the elevation of the top of the depressed curb should be 7 inches below the top of a theoretical 8-inch curb lane, 6 inches below the top of a 7-inch curb face, 5 inches below a 6-inch curb face, etc. These streets are subject to erosion problems, as discussed in Subsection 535. 211.
E 535.24 Streets With No Curb and With or Without Pavement
Generally, streets that are unimproved or partially improved have little or no drainage control, as discussed in Subsection E 535.211. Where there is no existing or proposed curb on the street, construction of the driveway curb, which may extend into the traveled roadway, may constitute a traffic hazard. Therefore, adequate safety measures must be added to warn or divert traffic. These measures may include installation of such appurtenances as guard rail, warning rail, or guideposts; also grading, the construction of temporary berms, etc. When the street is further improved, these protective devices may be modified or removed.
If installing these protective devices is not deemed desirable, it may be advisable to use a temporary asphalt driveway. See Section E 531, Types of Pavement. The asphalt driveway is then constructed to the established grade. The pavement is constructed flush with the surface, and curbs are omitted.
E 535.3 On Private Property
The proposed street and driveway grades should be adjusted to avoid any abrupt grade or alignment difference between such driveway within the public street and the existing driveway on private property. Where this abrupt difference cannot be eliminated, a sufficient portion of the driveway located on the abutting property should be removed. A smooth transition can then be constructed to offset these differences.
The Department of Building and Safety standards for driveways on private property should be met, where possible. These standards are:
- The grade used for access to any garage or required parking area should not exceed 20 percent.
- The cross slope of the driveway should not exceed 10 percent.
- The maximum slope of a required parking space in any direction should not exceed 5 percent.
- The minimum dimensions for the above parking space should be 8 by 18 feet.
- The minimum vertical clearance for the vehicle entrance to the garage is 6 feet, 6 inches. This should be considered in changing the driveway grade or approach slab elevation.
Where right of entry or easements are required for work done on driveways, the right of way sketch should show the maximum grade to which the driveways are to be reconstructed.
E 535.4 Design Check of Vehicular Vertical Clearance
The Bureau may permit the driveway grade on private property to exceed 20 percent. However, the most critical section of any driveway design should always be checked for vehicular vertical clearance and negotiability.
A suggested method is to use the clear plastic automobile templates which are included in the pocket of the cover of this Part of the Manual. These templates are designed as the composite shortest and longest vehicles referred to in Section E 322, Vehicular Clearances. They have been scaled to 1-inch equals 2 feet horizontally and vertically.
For testing the traversability of the driveway, the profile of the most critical vehicular paths should be plotted on 10 x 10 cross-section paper. The most critical path is usually where the vehicle is backing out of the driveway toward the uphill direction of the street. The profile should be plotted on the same scale as the templates; that is, 1-inch equals 2 feet horizontally and vertically. This profile should include the length of the existing or proposed street grade. The plotting should extend from the driveway onto the street to at least the street centerline or along the probable path of a vehicle both entering and leaving the driveway. It should also include a length of plotted profile of the existing driveway extending from the property line onto the abutting property a sufficient length to permit the vehicle’s access to such property. The proposed driveway grade is then superimposed between these limits.
The templates should be moved along the plotted profile, noting whether any under portion of the vehicle touches the profile line. Any contact with the vehicle with the profile line should be avoided by design adjustments. When using this testing and design procedure, it may be found that satisfactory vehicle access cannot be economically provided. (This information should be transmitted to the Bureau of Right of Way and Land according to the procedure outlined in Section E 800, Procedural Steps for Proposed Improvements.)1
Footnotes
- The text in parenthesis is from the legacy Street Design Manual text and is no longer in use.
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