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Section 4: Profiles

Public driveways and commercial driveways should be constructed with a vertical curve between the pavement cross-slope and the driveway approach and between changes in grade within the driveway throat length. A private residential driveway may be constructed without vertical curves provided that a change in grade does not adversely affect vehicle operations. Typically a change in grade of three percent (3%) or less and a distance between changes in grade of at least eleven feet [3.3 m] accommodates most vehicles. However, literature suggests that a six percent (6%) to eight percent (8%) change in grade may operate effectively. Individual site conditions should be evaluated to accommodate the vehicle fleet using the driveway.

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Driveway Grades

To achieve satisfactory driveway profiles, some of the significant factors to be considered are:

  1. Abrupt grade changes, which cause vehicles entering and exiting driveways to move at extremely slow speeds, can create:
    • The possibility of rear end collisions for vehicles entering the driveway.
    • The need for large traffic gaps that may be unavailable or infrequent, causing drivers to accept inadequate gaps.
  2. Where sidewalks are present, or in developing areas where pedestrians may be expected now or in the future, slower turning speeds may be beneficial and special design requirements apply. See Section 6 for more information.
  3. The comfort of vehicle occupants and potential vehicle damage, (i.e., prevent the dragging of center or overhanging portion of passenger vehicles).
  4. Grades must be compatible with the site requirements for sight distance and drainage, to prevent excessive drainage runoff from entering the roadway or adjacent property.

Because a large combination of slopes, tangent lengths, and vertical curves will provide satisfactory driveway profiles, some generalizations should be considered relative.

On curb and gutter sections, placement of vertical curves should be at the extended gutter line and not closer to the travel lanes unless curb and gutter returns and proper drainage are provided. On curb and gutter sections, the entire curb and gutter for the length of the curb cut should be removed and the gutter pan recast as an integral part of the driveway apron.

As shown in Table C-4, the suggested changes in driveway grades with a vertical curve (between the pavement cross slope and the driveway apron slope) are approximately 10 percent for private residential driveways and approximately 8 percent for all other driveways.

Anchor: #i1006176Table C-4. Suggested Change in Grade with a Vertical Curve

Driveway

Change

in Grade (A)(1)

Private Residential Driveways

10%

All Other Driveways

8%

(1)Change in grade between the pavement cross-slope and the driveway apron slope



Construction practice can provide a suitable sag vertical curve between the pavement cross-slope and the driveway apron when the apron length La (see Figure C-8) is equal to or greater than 20 feet [7 m].

Suggested Dimensions to Achieve an Appropriate
Vertical Curve (click in image to see full-size image) Anchor: #XWLGDHFSgrtop

Figure C-8. Suggested Dimensions to Achieve an Appropriate Vertical Curve

Maximum driveway grades should be limited to 12 percent for private residential driveways and to 8 percent for other driveways. Where possible, the driveway grade should be limited to 6 percent or less within the roadway right-of-way.

A construction easement is required for construction beyond the right-of-way line. For construction beyond the right-of-way, it is necessary for the property owner to furnish the construction easement or right of entry required.

Also, within the limits of curb return radii, no drop curb should be allowed except as required for curb ramps.

The length of the vertical curve between the pavement cross-slope and the driveway apron is a function of the algebraic difference in the grades. Table C-5 provides the desirable and minimum lengths for these vertical curves.

Anchor: #i1006192Table C-5. Length of Vertical Curve L (feet) For a Change in Grade Between the Pavement Cross-Slope and the Driveway Apron Slope

Change in

Grade,

A

 

 

 

 

Crests

 

Sags

 

Des.

Min.

 

Des.

Min.

 

ft (m)

ft (m)

 

ft (m)

ft (m)

4-5%

6-7%

8-10%

5 (1.5)

6 (1.8)

8 (2.4)

3 (0.9)

4 (1.2)

5 (1.5)

 

7 (2.1)

8 (2.4)

10 (3.0)

4 (1.2)

5 (1.5)

7 (2.1)

Rounded: Parabolic curvature. The plans may specify a particular type of curvature.

Des.: Desirable Minimum Length

Min.: Minimum Length

Where practical, greater lengths should be provided to achieve a flatter and smoother profile.

C-9 through C-11 illustrate typical driveway profiles.



The length of the vertical curve at other points of driveway grade change is also a function of the algebraic difference in the grades. Table C-6 provides the typical lengths for these vertical curves.

Figures C-9 through C-11 illustrate typical driveway profiles.

Anchor: #i1006238Table C-6. Typical Length of Vertical Curve, L, For Change in Grade in Driveway Profile

 

 

 

Crest

 

Sag

 

Change

in Grade

A

 

Private

Residential

Driveways

 

Other

Driveways

 

Private

Residential

Driveways

 

Other Driveways

 

ft (m)

ft (m)

 

ft (m)

 

ft (m)

4-5%

6-7%

8-10%

2 (0.6)

3 (0.9)

4 (1.2)

5 (1.5)

5 (1.5)

6 (1.8)

 

3 (0.9)

5 (1.5)

6 (1.8)

 

6 (1.8)

7 (2.1)

8 (2.4)



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Profiles on Curb and Gutter Sections

Roadway with Curb and Gutter, Driveway
Profiles on an Upgrade (click in image to see full-size image) Anchor: #AGRRWLOAgrtop

Figure C-9. Roadway with Curb and Gutter, Driveway Profiles on an Upgrade

Roadway with Curb and Gutter, Driveway
Profiles on a Downgrade (click in image to see full-size image) Anchor: #MKNYUUKIgrtop

Figure C-10. Roadway with Curb and Gutter, Driveway Profiles on a Downgrade

See Tables C-5 and C-6 for lengths of vertical curves.

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Profiles with Drainage Ditch

 Driveway Profiles on Roadway with Drainage
Ditch (click in image to see full-size image) Anchor: #LKVRKAPTgrtop

Figure C-11. Driveway Profiles on Roadway with Drainage Ditch

See Tables C-5 and C-6 for lengths of vertical curves.

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