The clear zone, or clear recovery area, is provided along highways to allow vehicles veering off the travel lane opportunity for safe recovery or stopping. The clear zone width (always measured from the edge of the travel lane) depends on several factors, including:

The

Roadway Design Manual

contains a full discussion of the clear zone and provides the minimum and desirable widths for various roadways.

Light poles should be offset at least 2.5 feet from the curb face. All pole offset dimensions shown in this section are measured to the pole centerline.

The clear zone table from the

Roadway Design Manual

is duplicated in Chapter 10 of this manual.

“House side mounting” refers to the placement of luminaires between the curb and right-of-way line.

“Median mounting” refers to placement on open medians or medians with concrete traffic barrier.

There are two types of poles used for conventional lighting: non-breakaway and breakaway. Non-breakaway poles are rigidly mounted, usually remaining upright when hit by a vehicle. Breakaway poles are designed so that the base will shear easily on impact. The table below briefly explains the advantages and disadvantages of both types when struck by an errant vehicle.

Because of their respective advantages and disadvantages, both types of poles have appropriate uses. However, unless special circumstances exist, breakaway poles are preferred over the non-breakaway type.

Breakaway poles should not be used in situations where they are more hazardous than non-breakaway poles and situations in which the breakaway feature would be useless. Breakaway poles are not normally used if:

Other considerations frequently come into play. The preceding list is provided only as an overview.

When a non-breakaway pole is used inside the clear zone, it must be protected from traffic. Acceptable methods of protection include mounting the pole:

Curbs are not considered adequate protection for non-breakaway poles.

Generally, non-breakaway roadway lighting poles may be used on the house side of roadways when placed outside of the clear zone or inside the clear zone when protected from impact.

Non-breakaway poles should be placed as close to the right-of-way line as lighting design and practicality permit. Wherever possible, non-breakaway poles should be placed among other nonyielding structures to minimize the hazard.

If non-breakaway poles are used and are not protected, the poles must be outside the clear zone and as close to the right-of-way line as possible subject to good lighting design practice.

Non-breakaway poles mounted behind metal beam guard fence should be placed at least 2.5 feet behind the guard fence

to allow for deflection of the guard fence if hit

.

Joint usage of poles is encouraged to reduce roadside clutter and the number of fixed objects along the roadside. When lighting is provided at signalized intersections and when conditions permit, the luminaires should be mounted on the traffic signal pole. Note that luminaires mounted on traffic signal poles should be powered from the signal electrical service.

Luminaires mounted on traffic signal poles should be oriented perpendicular to the centerline of the roadway being lighted.

To understand the use and placement of breakaway poles, it is important to understand the concept of “falling area.” Research shows that most errant vehicles striking light poles are traveling at an angle less than 20 degrees from their original path and that light poles fall within one mounting height from the foundation along the direction of vehicle travel. A breakaway pole falls within 2/5 (40 percent) of its mounting height in a direction perpendicular to and away from the lane in which the errant vehicle was traveling (see Figure 6‑3, “Falling area — final position of 50 feet luminaire support.”) Therefore, to prevent knocked down poles from encroaching onto other traffic lanes, breakaway poles should be placed so that they have a falling area of at least 2/5 of the mounting height behind the poles and one mounting height on the side of the pole.

EXAMPLE: In Figure 6‑3, the falling area is calculated as follows:

2/5 × 50 ft. mounting height = 20 ft. falling area

Unprotected roadway lighting poles located inside the clear zone should be breakaway, unless conditions dictate otherwise.

Breakaway poles placed on the house side of freeways should be 15 feet from lane edge and should provide a clearance behind the pole of 2/5 of the mounting height. For highways other than interstates, breakaway poles placed on the house side of travel lanes should be 15 feet from lane edge where practical. If sufficient right-of-way does not exist for this clearance, the poles may be placed just inside the right-of-way line, but not closer than 2.5 feet from lane edge.

For house side lighting, the poles should be located as far from the shoulder edge as practicable. Generally, the minimum should be 15 feet from the lane edge.

Figure 6-4 shows typical house side lighting of a controlled access roadway with a median less than 30 feet wide. If the median width were 30 feet or greater, then median lighting could be used.

Breakaway poles placed in medians should not be closer than 2/5 of the mounting height from either main lane edge. Breakaway poles should not be placed in medians less than 30 feet wide, except as noted in the following paragraph.

Median lighting in narrow medians should be avoided. If no other alternative is possible, an exception may be made for divided city streets with curbed medians, speed limit of 45 MPH or less, and where pedestrian traffic allows the use of breakaway poles. In this situation, breakaway poles may be used if placed at least 2.5 feet from any curb face, the pole height should not exceed 30 feet and pole mast arm lengths should not exceed 4 feet. Light poles should not be installed in urban median areas less than 30 feet wide if any other design is practical.

The turning lane of a divided city street may be included as part of the median width when determining the falling area. Remember, though, 2.5 feet offset from curb face should be maintained.

Breakaway poles placed in city street medians should also be placed at least one mounting height back from the end of the median at intersections.

Non-breakaway poles should not be placed in medians unless properly protected.

The following illustrations show typical median lighting designs for various controlled access roadway sections.

Example 1 — Unprotected Median:

Figure 6‑5 shows a typical median lighting design for a controlled access roadway having an unprotected median 30 feet or greater in width. Here breakaway poles should be used.

Example 2 — Concrete Median Barrier:

Figure 6‑6 shows a typical median lighting design for a controlled access roadway having a concrete median barrier. Median width in this situation is typically 20 feet.

The following table shows the recommended lighting for concrete median barriers.

Avoid placing lighting poles in channelizing (dividing) islands, as the falling area of the pole is difficult to obtain except in cases where the island is very large.

Figure 6-7 and Figure 6-8 show examples of breakaway pole placement and respective minimum applicable distances recommended for each of the cases listed in the following tables.

The distances shown and described in these guidelines as well as the clear zone definitions are minimum values. Even though breakaway poles may be placed in the clear zones, both breakaway and non-breakaway lighting poles should be placed as far away from the roadway as practical while maintaining the required light levels.

The Americans with Disabilities Act (ADA) accessibility guidelines (36 CFR, Part 1191) stipulate that public sidewalks, where provided, must contain a continuous passage at least 36 inches wide. For this reason, the placement of poles in sidewalks should be avoided. Where such placement cannot be avoided, the sidewalk may need to be widened around the pole to maintain the required passage.

Foundations for luminaire supports should be set flush with the ground line. Foundations placed on slopes should have the edge closest to the travel lanes flush with the ground.

Tests have shown that breakaway luminaire supports may not operate properly when the vehicle strikes the pole too high above the ground. Breakaway poles should, therefore, not be placed in areas where they are likely to be struck more than 28 inches above the top of the foundation. Limiting the negative side slopes to 1:6 between roadway and luminaire supports should ensure acceptable striking height.

, “Breakaway Light Poles,” provides a discussion of the frangibility requirements for breakaway poles.