Changing a Broken Sign Post in Ten Minutes or Less

Problem

Wooden signposts along California's highways are subject to being knocked down by errant drivers. Many of these, such as EXIT, MERGE, and STOP signs, are located in tight curves, narrow shoulders, and medians, where the task of replacing them creates hazardous traffic conditions for highway maintenance crews and the motoring public. Using typical methods, a two-person crew usually takes thirty to forty minutes to replace these signs, and more if a lane closure is required. Thirty-six Caltrans employees were fatally struck by vehicles between 1992 and June of 1999, some of them in the process of replacing signs. However, researchers at Caltrans have developed a simple method to reduce the time it takes to change a battered sign to just ten minutes. Ongoing field evaluations, with feedback from Caltrans crews, helped refine the design and installation to make them as simple and cost-effective as possible. The less time it takes crews to replace the signs, the less risk there is to their safety

Findings

The key to the quick change strategy is using a permanent concrete footing designed to accommodate wooden signposts that vary slightly in width and shape. Once the footing has been properly installed, signposts can be placed quickly by inserting them into a deep hole in the footing and securing them with two specially designed plastic wedges. The footing and the wedges fasten the sign upright in the face of wind and rain. If a vehicle strikes and breaks off the wooden post, the footing and wedges hold the stub of the post in place.

Replacing a broken post becomes a simple matter of prying out the wedges (using tools like pickaxes and crowbars that highway crews already carry), removing the broken post, placing a new one, and replacing the wedges. Where proper installation is carried out to begin with, it takes an average of ten minutes to exchange the signs.

The concrete footing specifically designed for this project is heavy enough (1600 lbs) to withstand the wind force on the face of the sign, and the hole for the signpost is deep enough to hold it upright and steady. This hole is slightly offset, which makes the footing somewhat thicker on the two sides which resist the force of an impact. To ensure that it is installed correctly, the footing is marked with an arrow indicating the direction of traffic flow. It's also reinforced with rebar to help prevent breakage, and has threaded inserts for hoisting it into place. Proper compaction of the soil when first installing the footing is crucial, so that rain and erosion do not cause it to lean or shift.

The wedges are made of a tough plastic (recycled carpet fibers formed into blocks by an extrusion process) that can be cut and shaped with ordinary hand and power tools, doesn't readily absorb water, and is environmentally benign. Their design allows for variations in the width of standard signposts, and only two of them are necessary to secure the sign firmly. They can become difficult to remove if they are hammered into place: practice has shown that only foot pressure is needed for them to do their job. Because of the shape of the footing and the placement of the wedges, this system won't work where signs are subject to being hit by wrong-way traffic.

The footings cost $100 to manufacture and $91 to install, but subsequent signpost replacements are $32 cheaper than current methods. This makes them financially reasonable for "high-hit" locations, where signs are knocked down five to six times a year. More importantly, the safety benefit from reduced worker and public exposure to hazardous traffic conditions makes the system extremely attractive.

There are currently several ongoing field evaluations (in Districts 1, 2, 3, and 4) to test the design and get feedback from highway crews on possible improvements.

For a full report on this, see http://www.dot.ca.gov/hq/newtech/research/qcsp/qcsp.htm