Crashworthy Work-Zone Traffic Control Devices (2006)

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13 CHAPTER 5 PERFORMANCE ASSESSMENT AND CATEGORIZATION Although the state of the practice presented in Chapter 3 shows that considerable progress has been made, further research in the area of work-zone traffic control devices is certainly warranted. Many of the existing crashworthy de- signs that are compliant with NCHRP Report 350 guidelines are proprietary. Although these devices meet performance requirements, they sometimes cost considerably more than some of the devices shop-fabricated from readily available materials. Primary among the Category 2 applications of interest under this project are portable sign supports, barri- cades, and barricades with sign attachments. A discussion of these applications is presented in the following sections. 5.1 PORTABLE TEMPORARY SIGN SUPPORTS Portable temporary sign supports are typically free-standing systems that have sign panels mounted at various heights. Low-mounting-height systems have mounting heights that range from 0.3 m to 0.9 m (1 ft to 3 ft) from the ground to the bottom of the sign. High mounting heights are defined as those with a mounting height between 1.5 m and 2.1 m (5 ft to 7 ft). The low-mounting-height systems present a design challenge because of their propensity to rotate into the wind- shield of the impacting vehicle. Most of the acceptable alter- natives available for this application are proprietary sign stands that must be used in combination with a roll-up fabric or vinyl sign panel. Although some of these systems can offer advantages such as portability, ease of erection, and adjust- able mounting height, their cost can sometimes be prohibi- tive. Furthermore, the use of a more rigid sign substrate is desirable to improve legibility and retro-reflectivity in windy conditions. High-mounting-height, portable sign stands are typically fabricated with larger support members. If the supports do not readily fracture or release upon impact, they may yield around the front of the impacting vehicle and carry either the sign panel and/or top of supports into the windshield. As with low-mounting-height sign stands, rigid sign panel substrates are more problematic with collisions of this nature. Remedial measures for these types of problems have involved weaken- ing the supports at or near bumper height, installing break- away mechanisms at bumper height, or providing sign panel release mechanisms. Sometimes combinations of these design modifications are incorporated. As mentioned previously, the configuration of the sign stand and selection of an appropriate sign substrate are equally im- portant in the design of a portable sign support system. Several generic sign stands with various sign substrates including ply- wood, aluminum, FRP, and corrugated plastic have been suc- cessfully tested. However, further work is needed to develop additional generic sign stand alternatives that can be used with rigid or semi-rigid sign substrates at different mounting heights. A review of the existing portable sign support systems yielded the following observations: • A large number of the devices are proprietary. • Most proprietary support devices are fabricated from square steel or aluminum tubing and are available with both rigid and non-rigid sign substrates. • Many of the proprietary X-base supports are adjustable for varying site conditions. • A small portion of the proprietary supports are fabricated from various plastics. • Generic supports are mostly fabricated with wood or plas- tic lumber, perforated steel tubing, and/or PVC pipe and are generally not well suited for varying site conditions. • Generic rigid sign substrates are generally fabricated with sign-grade plywood or aluminum. • Proprietary rigid sign substrates include laminated com- posites and extruded plastics. • Portable sign supports with signs mounted at 1.5 m (5 ft) or higher experience more favorable results in crash tests when some type of fracture or release of the support occurs near bumper height of the impacting vehicle or when early release of the sign panel is achieved. 5.2 BARRICADES AND BARRICADES WITH SIGN ATTACHMENTS Because the standards of some states permit the use of a barricade as a sign support for various project limit and guide signs, sign attachment mechanisms for some of the crash- worthy Type III barricade designs should be developed. Re- sults of full-scale crash testing indicate that existing wooden

14 Type III barricades, with or without sign panel attachment, pose potential hazards to impacting vehicles because of the propensity for the sign panel and/or fractured vertical supports to impact and penetrate the windshield. (3) Testing has also shown that, because of their rigidity and mass, the use of ply- wood sign substrates can be problematic at mounting heights ranging from 0.3 m to 1.5 m (1 ft to 5 ft). (3) Depending on the specific barricade design and sign attachment mechanism, a mounting height of 2.1 m (7 ft) is more accommodating of plywood sign substrates because direct windshield contact can be avoided. As mentioned in previous sections, full-scale crash testing has demonstrated the crashworthiness of improved Type III barricade designs constructed from materials such as perfo- rated steel tubing, steel angle sections, hollow-profile plastic (e.g., HDPE or PVC), and FRP. (3, 4, 10) Given that these generic barricades are crashworthy, the next step is to develop and evaluate appropriate sign panel attachment mechanisms. There are two basic sign attachment mechanisms. If the mounting height is sufficiently low, the sign panel can be attached directly to the barricade rails and supports. If a rigid sign substrate is used, the sign panel must be attached to the supports and not the rails alone. Wooden rails will fracture on impact and, therefore, can permit the sign panel to release and travel into the windshield of the impacting vehicle. Plas- tic rails may not possess sufficient stiffness to support the sign panel and accommodate wind loads. When taller mounting heights (e.g., 1.5 m to 2.1 m [5 ft to 7 ft]) are desired, the sign panel must be attached to support members that extend above the barricade. These support mem- bers can be attached to the barricade structure in one of two ways. In the first alternative, the sign support members are bolted directly to the barricade rails. This alternative requires the use of wooden rail elements since, as mentioned previ- ously, hollow-profile plastic rails are typically too flexible to support the sign panel and the required wind loads. Direct attachment to the wooden rails may be acceptable at the higher mounting heights if contact of the sign panel with the wind- shield can be avoided. In the second alternative, the sign supports can be bolted to cross braces extended between barricade supports or to the barricade supports themselves if the barricade width is not too great. The cross braces are provided in two locations behind the upper and lower barricade rails. Because the loads applied to the sign panel are not transferred through the bar- ricade rails, i.e., the barricade rails are not used as structural members, the rails can be either hollow-profile plastic or wood. The specific design details (e.g., sign support material type and size, connection methods, sign panel substrate, acceptable mounting height) may vary depending on the configuration of the barricade system to which the sign is being attached. Under the FHWA pooled fund project mentioned previ- ously (12), a perforated steel-tube barricade with a 1.2-m × 1.2-m (4-ft × 4-ft) plywood sign panel attached at a 2.1-m (7-ft) mounting height was successfully designed, devel- oped, and tested. Under this same project, a barricade system with PVC uprights and sign support members having a ply- wood sign panel of the same dimensions attached at the same mounting height did not pass crash testing. The researchers believe the deficiencies of this system can be overcome by using HDPE instead of PVC material for the barricade up- rights and sign supports. The HDPE is more ductile than PVC and would prevent fracture of the supports, thereby eliminating exposure of the connection bolts that penetrated the windshield of the test vehicle. A review of existing barricades and barricades with signs yielded the following observations: • A significant number of states use all-wood barricades that have not been crash tested. • A number of states have adopted the generic, crash- tested, perforated steel-tube design using both wood and hollow-plastic horizontal rails. • Proprietary Type I and II barricades are largely molded plastic, A-frame installations. • Generic Type I and II barricades are generally fabri- cated with steel angle and wood for A-frame installa- tions and perforated steel tube and wood for other Type I and II installations. • There are a wide variety of proprietary Type III barri- cades using many combinations of steel, PVC, HDPE, PP, aluminum, and wood. • Some states have indicated successful crash testing of all-wood Type III barricades, but reports have not been provided. • Information on barricades with signs indicates a limited number of successfully crash-tested devices. 5.3 RECOMMENDATIONS FOR PHASE II Based on the state-of-the-practice review and the avail- ability of generic, crashworthy designs manufactured from readily available materials in the different categories of inter- est, the researchers prepared a list of devices for considera- tion by the panel for further development and testing under Phase II of this project. The following sets of generic work- zone traffic control devices were selected by the panel for further development and testing under Phase II of the project: 1. Type III barricade with rectangular sign attached. 2. Small, portable work-zone sign with 1.2-m × 1.2-m (4-ft × 4-ft) rigid sign panel substrate mounted 0.3 m (1 ft) above ground. If design with rigid substrate is unsuccessful, use of a semi-rigid (hollow-plastic) sub- strate will be investigated. 3. Portable work-zone sign with rigid sign panel substrate mounted 1.5 m (5 ft) to 2.1 m (7 ft) above ground.

15 4. Type III barricade with good functionality, site adapt- ability, and attached warning lights. The scope of the first set was later expanded by the panel to also include 1.2-m × 1.2-m (4-ft × 4-ft) diamond-oriented sign panels in addition to the originally specified 0.8-m × 1.5-m (2.5-ft × 5-ft) rectangular sign panel. The first and fourth sets were combined such that testing of the barricade with sign also included an evaluation of attached warning lights. For each of these sets of work-zone devices, the researchers developed several design alternatives for review and prioriti- zation by the panel. The researchers used the panel’s prioriti- zation of the designs to formulate a full-scale crash testing plan for each set of devices. A total of 10 crash tests were con- ducted on the selected barricade and sign support systems. Details of the design, development, testing, and evaluation for each set of devices are presented in the following chapters of this report.