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MUTCD Guidelines For Sign Bases And Posts

Sign bases and posts play vital roles in maintaining public safety, because even the clearest signs will do little good if not properly supported.  The Manual on Uniform Traffic Control Devices (MUTCD) describes and regulates the various types of bases and supports commonly used.  The following information summarizes and discusses these rules.

 

Materials for Sign Supports

 

  • Wood

Wood is often used for sign bases as an economical alternative to steel.  The MUTCD does not prescribe the specific species of wood that should be used, but pressure-treated standard lumber pieces are often chosen, as they are infused with anti-rot chemicals to withstand decay for extended periods, even after prolonged exposure to the elements.

 

The MUTCD provides several guidelines for the size and use of wooden sign supports.  Posts can be either 4”x4” or 6”x8” in width, but in areas where breakaway signs are required, a 6”x8” post should have two 3” holes drilled through it.  These should be in a perpendicular direction from passing traffic.  Wooden posts should also be buried between 30” and 36” deep, depending on local soil conditions, wind levels, and the risk of theft or vandalism.  Using two posts to support a single sign is permissible if engineers feel that local conditions warrant their use, although placing poles closely together should be avoided if doing so is likely to affect crashworthiness.

 

  • U-Channel Steel Posts

Sign bases made of hot rolled steel are considered breakaway supports as long as they weigh less than 3lbs. per linear foot, as a vehicle strike to such a post will cause it to bend, break, or uproot.  The post should be buried no deeper than 42” underground, and installers should avoid using concrete to secure the base, as this will interfere with breakaway considerations.

 

If heavier-weight steel is used, the sign base should have a stub post installed at ground level to enhance breakaway.  Use of a stub post not only enhances safety in case of a vehicle collision, it also makes replacement or repair a simpler process.

 

  • Square Steel Tubes

Perforated steel tubes are commonly used as signposts, and they meet MUTCD breakaway standards as long as the posts measure no more than 2.25” in width.  These posts should be driven deep enough in the ground to prevent local winds or erosion from causing them to tip, and concrete should not be used around the sign base.  Steel assemblies or slip couplings can be used at ground level to make the sign easier to repair or replace in the event of a collision or other damage.

 

  • I-Beam Sign Supports

I-beams are used to support large road signs, and often there are two or more placed side by side.  I-beam posts provide exceptional support, but they also limit breakaway due to their inherent strength.  To remedy this issue, installers typically pour concrete and steel foundations for the supporting beams and then connect the beams onto break-away bases so that, in the event of a collision, the sign will slide out of and away from the base.

 

Temporary/Portable Signs

The MUTCD discourages the use of non-permanent signs when other methods are possible, but this is not always an option.  Some of the instances in which portable signs are warranted include the following: when permanent highway safety systems have been damaged or destroyed; when power outages make permanently installed signal devices useless; when other means such as local officers directing traffic by hand are not available; and when traffic needs to be controlled around school zones.  In such cases, a sign base designed for ease of transportation is recommended.  Portable signs should only be used on an as-needed basis and removed when not in use or no longer necessary.

 

The use of sign bases and posts remains an inexact science due to the necessity of balancing stability with breakaway factors.  By following the rules set forth in the MUTCD, however, engineers and installers can ensure that these important components in the nation’s traffic system continue to do their jobs safely and effectively.