Appendix B: Treatment of Pavement Drop-offs in Work Zones

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Section 1: Overview

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Scope

These guidelines apply to construction zone work where continuous pavement edges or drop-offs exist parallel and adjacent to a lane used for traffic. These guidelines do not apply to short term operations. The Texas Manual on Uniform Traffic Control Devices (TMUTCD) defines short term operations as daytime work from one to twelve hours.

These guidelines do not constitute a rigid standard or policy; rather, they are guidance to be used in conjunction with engineering judgment.

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Types of Treatment

Treatment may consist of either or both of the following:

  • warning devices (such as signs or channelizing devices)
  • protective barriers (such as concrete traffic barriers or metal beam guard fence).
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Factors Affecting Treatment Choice

The type of treatment (warning device or protective barrier or both) selected depends on several factors, including engineering judgement. These guidelines are based on the following factors:

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Factor

Definition

Notes

edge condition

slope of the drop-off

For more information, see “Edge Condition” subheading below.

Lateral clearance

distance from the edge of the travel lane to the edge condition

See Figure B-1 for description.

edge height

depth of the drop-off

See Figure B-1 for description.



 Definition of Terms. (click in image to see full-size image) Anchor: #i999011grtop

Figure B-1. Definition of Terms.

In addition to the factors considered in the guidelines, each construction zone drop-off situation should be analyzed individually, taking into account other variables, such as:

  • traffic mix
  • posted speed in the construction zone
  • horizontal curvature
  • practicality of treatment options.

    In urban areas where speeds of 30 mph [50 km/h] or less can be predicted for traffic in a particular construction zone, there may be a lesser need for signing, delineation, and barriers. Even so, sharp 90 degree edges greater than 2 inches [50 mm] in height, if located within a lateral offset distance of 6 feet [1.8 m] or less from a traffic lane, may indicate a higher level of treatment.

    If distance Y (as described in Figure B-1) must be less than 3 feet [0.9 m], use of positive barrier may not be feasible. In such a case, if a positive barrier is needed (according to Figure B-2), then consider one of the following:

  • moving the lane of travel laterally to provide the needed space
  • providing an edge slope such as Edge Condition I.
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Edge Condition

“Edge condition” refers to the slope of the drop-off. The following table describes three edge condition types used in these guidelines. These edge conditions may be present between shoulders and travel lanes, between adjacent or opposing travel lanes, or at intermediate points across the width of the paved surface. Due to the variability in construction operations, tolerances in the dimensions shown in the figures may be allowed by the engineer.

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Condition Type & Description

Notes

Edge Condition I

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S = 3:1 or flatter slope rate (H:V)

Most vehicles are able to traverse an edge condition with a slope rate of 3 to 1 (horizontal to vertical) or flatter. The slope must be constructed with a compacted material capable of supporting vehicles.

Edge Condition II

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S = 2.99:1 to 1:1 slope rate (H:V)

Most vehicles are able to traverse an edge condition with a slope between 2.99 to 1 and 1 to 1 (horizontal to vertical) as long as D does not exceed 5 inches [125 mm]. Undercarriage drag on most automobiles will occur as D exceeds 6 inches [150 mm]. As D exceeds 24 inches [0.6 m], the possibility of rollover is greater for most vehicles.

Edge Condition III

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S is steeper than 1:1 slope rate (H:V)

Slopes steeper than 1 to 1 (horizontal to vertical) where D is greater than 2 inches [50 mm] can present a more difficult control factor for some vehicles, if not properly treated. For example, in the zone where D is greater than two up to 24 inches [50 mm to 0.6 m] different types of vehicles may experience different steering control at different edge heights. Automobiles might experience more steering control differential in the greater than 2 up to 5 inch [50 to 125 mm] zone. Trucks, particularly those with high loads, have more steering control differential in the greater than 5 up to 24 [50 mm to 0.6 m] zone. As D exceeds 24 inches [0.6 m], the possibilities of rollover is greater for most vehicles.

NOTE: Milling or overlay operations that result in Edge Condition III should not be in place without appropriate warning treatments, and these conditions should not be left in place for extended periods of time.



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Guidelines for Treatment

The following guidelines show the recommended treatment for given combinations of edge condition, lateral clearance, and edge height. Remember to consider other factors listed above and use engineering judgment.

Anchor: #i1001421Treatment Guidelines for Pavement Drop-offs in Construction Work Zones

Edge Condition

Lateral Clearance

Edge Height

Usual Treatment (See Note 3)

I

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(slope is 3:1 or flatter)

30 ft. [ 9 m]

0 to 1 in.

[0 to 25 mm]

no treatment

-

--

>1 to 2 in.

[>25 to 50 mm]

CW 8‑11 signs

-

--

> 2 in.

[> 50mm]

CW 8‑9a or CW 8‑11 signs plus channelizing devices

-

> 30 ft. [> 9 m]

Any height

no treatment

II

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(slope is between 2.99:1 and 1:1)

20 ft. [ 6 m]

0 to 1 in.

[0 to 25 mm]

no treatment

-

-

>1 to 2 in.

[>25 to 50 mm]

CW 8‑11 signs

-

-

>2 to 5 in.

[>50 to 125 mm]

CW 8‑9a or CW 8‑11 signs plus channelizing devices

-

-

>5 to 24 in.

[>125 to 600 mm]

CW 8‑9a or CW 8‑11 signs plus drums

(see Note 1)

-

-

> 24 in.

[> 600 mm]

Check indications for positive barrier

(See Note 2)

-

> 20 ft. but 30 ft. [> 6 m but 9 m]

0 to 1 in.

[0 to 25 mm]

no treatment

-

-

>1 to 2 in.

[>25 to 50 mm]

CW 8‑11 signs

-

-

> 2 in.

[> 50mm]

CW 8‑9a or CW 8‑11 signs plus channelizing devices

-

> 30 ft. [> 9 m]

Any height

no treatment

III

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(slope is steeper than 1:1)

20 ft. [ 6 m]

0 to 1 in.

[0 to 25 mm]

no treatment

-

-

>1 to 2 in.

[>25 to 50 mm]

CW 8‑11 signs

-

-

>2 to 24 in.

[>50 to 600 mm]

CW 8‑9a or CW 8‑11 signs plus drums

(see Note 1)

-

-

> 24 in.

[> 600 mm]

Check indications for positive barrier

(See Note 2)

-

> 20 ft. but 30 ft.

[> 6 m but 9 m]

0 to 1 in.

[0 to 25 mm]

no treatment

-

-

>1 to 2 in.

[>25 to 50 mm]

CW 8‑11 signs

-

-

> 2 in.

[> 50mm]

CW 8‑9a or CW 8‑11 signs plus channelizing devices

-

> 30 ft. [>9 m]

Any height

no treatment

NOTE: Where restricted space precludes the use of drums, use channelizing devices. An edge fill may be provided to change the edge slope to that of the preferable Edge Condition I.

NOTE: Check indications for positive barrier (Figure B-2). Where positive barrier is not indicated, CW 8‑9a or CW 8‑11 signs plus drums may be used (with Note 1 also applying) after consideration of other applicable factors.

NOTE: Channelizing devices for the purpose of dropoff conditions are defined as: vertical panels, edge-line channelizers, or drums.



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Use of Positive Barriers

provides a practical approach to the use of positive barriers for the protection of vehicles from pavement drop-offs. Other factors, such as the presence of heavy machinery, construction workers, or the mix and volume of traffic, may make positive barriers appropriate, even when the edge condition alone may not justify the barrier.

NOTE: An approved end treatment should be provided for any positive barrier end located within a lateral offset of 20 feet [6.0 m] from the edge of the travel lane.

Conditions Indicating Use of Positive Barrier. (click in image to see full-size image) Anchor: #i1000532grtop

Figure B-2. Conditions Indicating Use of Positive Barrier.

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