Deflection Limits for Temporary Concrete Barriers

Whenever a traffic control plan is developed that utilizes temporary barriers, it is important to define acceptable barrier deflection criteria. However, the acceptable deflection criteria can be expected to vary, depending on the application. When temporary concrete barriers are used on the edge of a bridge, the risk of the entire line of barriers falling off of the deck requires that deflection limits be selected to preclude such behavior in almost all impact scenarios. Hence, it is recommended that at the edge of a bridge deck, design deflection limits should be selected to contain more than 95 percent of all crashes. In all other barrier applications, the consequences of a barrier exceeding the design deflection criteria are not severe. In these situations, a more modest deflection limit criterion based on an 85″ percentile impact condition is more appropriate. Previous crash testing according to NCHRP Report No. 3 SO has shown that most temporary barrier systems have produced large lateral deflections, high vehicle climb, and high roll angles when subjected to such an extreme impact. However, it is generally accepted that the Test Level 3 (TL-3) strength test with a ‘/4-ton pickup truck represents an extreme impact severity that is infrequently encountered in real world accidents. Additional crash tests could be conducted to determine the deflection of temporary barriers at reduced impact condition but the cost would be extremely high. Therefore, computer simulation was used to estimate the deflection of barriers impacted under the 85″ percentile impact conditions. Finally, recommendations were made pertaining to the two different design deflection limits that should be used for the Iowa temporary concrete barrier.