For the past 15 years, NCHRP Report No. 350 established the guidelines used to test roadside hardware, including work-zone devices.To become a crashworthy, FHWA-accepted device, work-zone systems were crash tested at Test-level 3 of NCHRP 350. This included 2 tests, which were conducted with a one-thousand, eight hundred and eight pound small car, the 820C, impacting at 22 and 62 mph. The low-speed test was usually omitted for devices weighing less than 100 lbs. Devices were normally tested at 0 degrees, which is head-on to the sign as normally placed on roads, and 90 degrees, which is end-on to the sign which may occur at the intersection of roads.A system could not penetrate the windshield or any of the occupant compartment, and significant windshield cracking and deformation could not occur.It was recommended that a four-thousand, four-hundred and nine pound pickup truck, the 2000P, be used in lieu of or in addition to the small car tests when occupant compartment penetration was the primary concern. Penetration was almost always the primary concern, but the recommendation was ignored.
Work-zone devices over the past 10 years have only been tested with the 820C small car, which is not very representative of the current vehicle fleet.These devices were tuned to small car geometry, for example, by extending the mast height of WZ sign stands so it will easily pass over top the car and not impact the windshield, as shown in the picture.In 2003, 18 bogie tests with a pickup truck frame were conducted at MwRSF. All sign systems tested were existing, FHWA-accepted systems. Some of these systems showed a potential for failure.NCHRP 350 was recently replaced by the Manual for Assessing Safety Hardware, or MASH, which requires both small car and pickup truck testing for work-zone devices. The problem is that current work-zone sign systems may not meet the new evaluation criteria, due to the fact that vehicles are currently heavier than they were 15 years ago and the geometry of the vehicles has changed.
This is a high-mounted sign system was an aluminum panel oriented at 90 degrees.[PLAY]The aluminum panel penetrates the windshield area, which may cause a safety concern.
The research objectives were first, to determine if existing crashworthy work zone sign systems will meet the new MASH standards. Then, to identify work-zone hardware parameters that increase the propensity for failure. And finally, to provide guidelines and recommendations about which parameters of work-zone systems are likely to have an unsafe performance.
The research consisted of an analytical study that included all full-scale tests previously conducted at MwRSF. From thefull-scale tests, individual hardware features of sign stands were studied to select work zone sign systems that showed a propensity for failure with MASH criteria. The hardware features considered were the properties of the actual systems as tested including the base, mast, sign panel, etc. Based on the analytical study, a total of 4 full-scale tests were conducted with systems that had the potential for failure. There were 2 small car tests and 2 pickup truck tests, with 2 systems per test. So a total of 4 systems were tested with each vehicle.
There were 157 previous tests conducted with a small car that were used in the analysis. There were an additional 18 simulated pickup truck frame bogie tests that were also analyzed for the pickup truck only. All systems, including both successes and failures of NCHRP 350 criteria were included in the analytical study. The system parameters and results from each of the system tests were documented in one comprehensive table.
System parameters are the heights, dimensions and materials of the important features of work zone signs. The 2 systems shown are two typical work zone systems. The one on the left is a X-footprint base, which is classified by its X-shaped legs, and the one the right is a parallel dual uprights base, which has two parallel legs. The basic parameters of sign systems are labeled. At the top there may or not be flags with a flag holder. The main support structure is a mast which may have telescoping stages, so the system is more compact when not in use. The sign panel may be aluminum, plywood, or a flexible vinyl material. Then there is a sign-locking mechanism which holds the sign in place, like the rigid brackets in the left or the bolted connection in the sign on the right. The base usually consists of vertical or horizontal springs and legs.
5 methods of failure were considered for all MwRSF work zone sign tests. These are severe windshield cracking and failure, windshield indentation, windshield penetration, other occupant compartment penetration, and roof deformation. From NCHRP 350, the methods of failure were not objectively defined. In MASH, windshield indentation is limited to less than 3 inches and no tear in the plastic liner, and roof deformation is limited to less than 4 inches. Windshield penetration, occupant compartment penetration and roof deformation are considered the more critical failures, because they have the potential to comprise the safety of the occupant more so than windshield indentation or cracking
To make predictions on how systems would perform with MASH criteria, vehicle parameters were evaluated for the old and new test vehicles. The hood length, height to bumper, height to roof, windshield angle measured from horizontal, and windshield length were five vehicle parameters important to consider. Since previousfull-scale tests were done with the 820C small car, predictions for the 1100C and 2270P vehicles were made by comparing to the 820C dimensions. As shown in the table, the small cars had small differences in dimensions except height to bumper. The pickup trucks mainly differed in hood length, windshield angle and windshield length.
Sign trajectory was predicted by comparing vehicle dimensions to prior test videos and photos. Each system was then given a ranking from 1-4 based on the chance of failing MASH. A 1 designates the systems with the highest chance of failure base on my predictions and a 4 has the lowest chance of failing MASH. The systems with a Ranking of 1 and 2 had a fairly significant chance at failure, and these systems were considered to be the most critical for the rest of the analysis.
If 50% of more of systems that had a given parameter were predicted to fail the MASH requirements, then the parameter was important.The important parameters for both vehicles are height to top of mast, sign panel material, mast stages, mast material, flag staff material, and orientation.Parameters important only for the small car are height to top of flagsand sign-locking mechanism.The parameter important only for the pickup truck was base layout.
Next, the important parameters were used to analyze entire systems. Systems were considered that were ranked either a 1 or 2, which were a 50-100% predicted chance of failing MASH, by the 3 most critical methods of failure: windshield penetration, other occupant compartment penetration or roof deformationSystems were analyzed by sorting systems by combinations of important parameters. The different combinations of parameters were considered to be systems with a high likelihood of failure.
These are the general categories of systems that were found to be critical for failure with the pickup truck and were recommended for testing.Each of the red bullets describes the parameters of one system that might be critical for failure with MASH.For example, a low-mounted sign system with an X-footprint spring base with flags with either an aluminum or vinyl panel at a 0- or 90-degree test orientation was believed to be critical for failure.
The same done for the small car, and these were the general categories of systems that were found to be critical for failure with the small car and were recommended for testing.
Based on the analysis and crash testing program, these WZ hardware parameters were determined to be important for causing failure with MASH evaluation criteria. Aluminum sign panel material is important for both the pickup truck and the small car.The critical range for the height to the top of the mast for the pickup truck is 75 to 135 in. and the critical range for the height to the top of the mast for the small car is 59 to 110 in. The presence of flags was more critical for the pickup truck without flags, and both with and without flags can be critical for the small car, depending on the specific system. The sign locking mechanism, and specifically rigid brackets, needs to be evaluated for each system to determine if the sign panel will or will not disengage upon impact with the small car. The X-footprint base is critical for the pickup truck, especially in the 0 degree orientation when the legs have an increased opportunity to penetrate the floorboard. Other parameters may be contributing to the safety performance of work zone sign support systems, but these are some specific parameters that manufacturers need to be aware of that may cause an unsafe performance, especially with certain combinations.
Four flowcharts were created as design aides for determining the performance a system will have with MASH. These were done for the small car and pickup truck for X-footprint base and dual upright base work zone signs. Chance of Failing MASH rankings are 1 for 75-100% chance of failing MASH, 2 for 50-75%,3 for 25-50%, 4 for 0-25%, and 5 if unknown GIVE AN EXAMPLEThe other flowcharts can be found in the report referenced on the final slide.
Safety Performance of WorkZone Devices under MASH Testing
Safety Performance of Work- Zone Devices under MASH Testing Jennifer Schmidt Graduate Research Assistant Midwest Roadside Safety Facility Nebraska Transportation Center University of Nebraska-Lincoln
Midwest Roadside Safety Facility Disclaimer The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presentedherein. This document is disseminated under thesponsorship of the Department of Transportation University Transportation Centers Program, in the interest of information exchange. The U.S.Government assumes no liability for the contents or use thereof.
Midwest Roadside Safety FacilityObjectives• New crash standards for work zone sign supports• Some of the previously accepted supports crash tested with NCHRP Report 350 may produce an unsafe interaction with certain passenger vehicles• Potentially unsafe design parameters for work zone sign supports when testing with MASH
Midwest Roadside Safety Facility Background• NCHRP Report No. 350• Crash test conditions at Test- Level 3 (TL-3) – 1,808-lb small car (820C) • 22 mph 0°Orientation • 62 mph – Normally tested at 0°and 90° orientations – 4,409-lb pickup truck (2000P) not used 90°Orientation
Midwest Roadside Safety Facility Problem Statement• Work zone signs only tested with small car• Systems tuned for small car• Simulated pickup truck tests indicated failure• MASH requires pickup truck testing• Current WZ sign systems may not meet MASH
Midwest Roadside Safety Facility Pickup Truck Bogie Testing Potential for sign to penetrate windshield6
Midwest Roadside Safety FacilityResearch Objectives• Determine if current WZ sign systems meet MASH• Identify WZ hardware parameters that increase propensity for failure• Provide guidelines and recommendations
Midwest Roadside Safety Facility Research Plan• Analytical study – Evaluate all full-scale tests – Study individual hardware parameters – Select work zone sign systems with a propensity for failure• Conduct 4 full-scale tests – 2 small car and 2 pickup truck – 2 systems per test
Midwest Roadside Safety FacilityPrevious Testing• Small Car Crash Tests – 157 full scale• Pickup Truck Tests – 157 full scale – 18 bogie tests
Midwest Roadside Safety Facility Important Parameters for Failure • ≥50% of systems with a parameter were predicted to fail for either vehicle • Both Vehicles • Car Only – Height to top of mast – Height to top of – Sign panel material flags – Mast stages – Sign-locking mechanism – Mast material • Truck Only – Flag staff material – Base layout – Orientation1
Midwest Roadside Safety Facility System Analysis• Systems that were predicted to fail MASH by: – Windshield penetration – Other occupant compartment penetration – Roof deformation• Analyzed systems based on combinations of important parameters
Midwest Roadside Safety FacilityCritical Parameters for 2270PTest FailureLow-Mounting Height High-Mounting Height• X-footprint base • X-footprint base – Spring base – Spring base or slipbase – Aluminum and vinyl panel – Aluminum panel – 0 and 90 degree orientations – 90 degree orientation – With flags – With flags• Parallel Dual Uprights • Parallel Dual Uprights – Aluminum panel – Aluminum panel – 0 degree orientation – 90 degree orientation – Without flags – Without flags
Midwest Roadside Safety FacilityCritical Parameters for 1100CTest FailureLow-Mounting Height Low-Mounting Height• X-footprint base • Parallel Dual Uprights – Spring base – Aluminum Panel – Flags – 0 and 90 degree orientations – Aluminum panel @ 0 degree – No flags orientation – Vinyl panel @ 90 degree orientation
Midwest Roadside Safety FacilityTest Summary• 3 of the 8 systems passed MASH evaluation criteria – 3 of the 4 systems failed with the pickup truck – 2 of the 4 systems failed with the small car• Comparing systems with similar parameters can be difficult
Midwest Roadside Safety Facility Important for MASH Failure Designers cautioned against using important parameters Parameter Pickup Truck Small Car Sign Panel Material Aluminum Aluminum Height to Top of Mast 75-135 in. 59-110 in. With and Without Presence of Flags Without Flags Flags Both 0 and 90 Both 0 and 90 Orientation degrees degrees Sign Locking Mechanism NA Rigid Brackets Base Layout X-footprint NA
Midwest Roadside Safety FacilityDesign Aides 11Breakaway Mechanism Height: Low ≤ 24”, High > 24” or no breakaway mechanism2Chance of Failing MASH: 1 - 75 to 100%, 2 – 50 to 75%, 3 – 25 to 50%, 4 – 0 to 25%, 5 –Unknown