Experimental Study of Breakaway Highway Sign Connections

Highway signs require breakaway base connections. These connections will slip under impact, therefore preventing injuries to the occupants of an impacting vehicle. The breakaway connection works as long as the tension of the bolts is maintained between an allowable range. A method to ensure that the bolts are tensioned to the proper value is presented. It is based on the use of Belleville spring washers. Laboratory and field tests were performed to verify the adequacy of the new method. Seven signs were selected along Florida highways. At each sign, the variations of tension in bolts installed with flat washers and with spring washers were monitored over a period of 1 year. The measurements showed that, at the time of installation, the new method was significantly more effective in ensuring the proper tension in the bolts. Similarly, over the long term, the bolts installed with spring washers maintained the tension in the bolt more effectively and without any loosening. The effectiveness of the breakaway connection with spring washers was also demonstrated during an actual car accident.