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Wetland Trail Design and Construction

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Finishing Details - (continued)

Pedestrian Railing Types

Inadequate railing systems have high potential for failing and injuring visitors. We recommend engineering review of railings and their connections.

Safety must be the first consideration in selecting a railing system. Safety requirements are primarily determined by the relative accessibility of the trail. Railing types must fit the appropriate Recreational Opportunity Spectrum class. Railings are of three basic types:

  • Railings attached to buildings, such as visitor centers, must meet building code requirements such as the Uniform Building Code (UBC) 509. This code requires a railing at least 42 inches high that a 4-inch sphere will not pass through.

  • Handrails on bridges need to meet the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges. Although most of the structures described in this book are not bridges, we offer these specifications for information. AASHTO requires 42-inch-high guardrails on all pedestrian highway bridges. Bridges on fully handicapped-accessible trails usually need this type of railing. This code requires handrail at least 42 inches high for pedestrian traffic and at least 54 inches high for bicycle or equestrian traffic. A 6-inch sphere must not pass through the railing in the bottom 27 inches, and an 8-inch sphere must not pass through the area above 27 inches.

  • Handrails for more remote trail bridges must be at least 42 inches high for pedestrian traffic and at least 54 inches high for bicycle or equestrian traffic. These handrail systems must also have at least one intermediate rail so that vertical distances between rails do not exceed 15 inches. Three-fourths of all Forest Service trail bridges fall in this category.

Not all wetland trail structures need railings. If the trail itself has more hazardous drops than the trail bridge would have without a handrail, a handrail is probably not required. Other considerations, such as convenience, may justify installing a handrail. Although UBC requirements and AASHTO specifications do not govern trail construction, they can serve as guidelines. As a general rule, any fully accessible trail with a drop of 4 feet or more, or a more remote trail with a drop of 8 feet or more, should have a pedestrian railing system. All accessible trails should at least have a curb. A wheelchair handrail is required for any accessible trail bridge on a grade of 5 percent or steeper.

Railing Installation

Install the railings after the posts and deck are complete. Most railings consist of a top and bottom rail, usually 2 by 6s, although 3 by 6s make a better splice and a stronger rail. The stronger rail permits posts to be spaced more widely than if 2 by 6s were used for rails. The rail can also be cut and drilled in a shop where the splices can be cut accurately and more efficiently.

Often there is no clear direction regarding splicing the railings if the span exceeds 16 feet, the longest lumber that is readily available. It is difficult to butt splice a railing to the surface of a post that is less than 6 inches wide without an awkward splice or a maintenance problem (figure 61).

Image of rail splices
Figure 61-Four methods of splicing rails.
It is best to cut the rails in the shop.

Walking on the top rail is a potential problem. Round logs or poles have been used to discourage visitors from walking on them, as well as 4 by 4s and 6 by 6s laid diagonally with one corner up. Another technique is to cut the tops of all posts at an angle and place a 2 by 6, or 2 by 8, on the cut surface.

The edges of all rails should be "edges eased." Edges eased is a trade term indicating that the corners along the edges of the piece of wood are rounded. To reduce splinters, the radius of the handrail edge should be ½ inch or more.

Installing a handrail on a curved bog bridge or angled boardwalk can be a challenge. One way to do this is to use steel angles. Measure the distance between posts and cut the rail to that length. Nail or screw the angles at the ends and to the outside of a 2- by 4-inch or 2- by 6- inch rail. The angles will have to be bent slightly to conform to the different alignment of the posts. Hold the rail in place and nail or screw the angle to the side of the post with the inside face of the board flush with the inside face of the post. Measure the distance between the centerline of the two posts and cut a 2 by 6 to that length. Round the ends slightly and bolt the 2 by 6 to the 2 by 4. The result will be a stronger rail than a single piece of material. This technique may also be used for straight sections of railing to avoid nailing or screwing into the face of the post (figure 62).

Image of rail installation on curved boardwalks
Figure 62-One method of installing rails on curving boardwalks using steel angles
bent to accommodate the curvature of the structure.

For rails on curved trails, short wedge-shaped pieces of lumber can be used as shims between the posts and the rails. The wedges should be oak or cedar. Wedges are difficult to cut in the field. You could notch posts to the correct angle to accept the rails, but this is also difficult.

Cable or wire rope can be used as a railing system in some specialized applications (figure 63). Often the posts are close, 4 to 6 feet, and the cable is strung through holes drilled in the posts or through screw eyes. A single piece of cable may be strung through all the holes in the upper part of the posts, down the last post to the next lower hole and continuing this process back to the beginning through the lower holes, reducing the need for many splices. Use cable tensioners as needed.

Photo of wire rope
Figure 63-Wire rope is used here as part of the railing system.

Curbs (Bull Rails)

Curb and bull rail are two names for the same thing. If the drop from a boardwalk is about 30 inches or less, a curb is usually installed. A curb is required for accessible trails. Curbs present a potential tripping hazard for pedestrians (figure 64).

Image of curbs (bull rails)
Figure 64-Curbs or bull rails are typically used
when the deck is no more than 30 inches off the ground.

Curbs placed directly on the surface of a wood deck can cause the deck planking to rot. Leaves, needles, and dirt accumulate against the curb, absorb water, and cause additional rot. During the winter, ice and snow will build up on the deck, causing a hazardous condition.

To keep the deck from rotting, place the curbs on blocks. A finished block of 2 by 4 lumber is only 1½ inches thick. Leaves and dirt can still build up against the curb and under it. With just 1½ inches of space between the curb and the deck, it is difficult to get a shovel under the curb, making this area almost impossible to clean. A better solution is to use two blocks of 2 by 4 lumber, one on top of the other, or one block of 4 by 4 lumber (figure 65). The increased clearance under the curb will not trap litter, and melting ice and snow will run off more quickly.

Image of the clearance under a curb
Figure 65-Having at least 4 inches
of clearance under the curb is best.

Bulkheads (End Dams, Faceplates)

Bulkheads must be installed where wood construction meets the earth trail at each end of a puncheon, bog bridge, or boardwalk. Faceplates function as retaining walls to support the earth. They also protect the end grain of the stringers from rot and insect damage (figure 66).

Image of bulkheads
Figure 66-Bulkheads serve as retaining walls to support
the earth, and they protect the stringers from rot and insect damage.
Here are two different ways to install them.

There are two ways to install a faceplate, depending on the climate. The faceplate may be installed with its top level with the top of the deck. This installation will leave a small gap between the deck plank and the faceplate, allowing some water to percolate down to the absorbent end grain of the stringer. In a dry climate, the amount of water is negligible. However, in a wet climate it is common to install the faceplate's top level with the top of the stringers, covering the gap with a piece of deck plank. If the faceplate is level with the deck, the exposed outside edge should be rounded to a ½- to 1-inch radius.

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Updated: 4/14/2014
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