MASH (AASHTO’S MANUAL FOR ASSESSING SAFETY HARDWARE)
WHAT IS MASH 2016?
AASHTO’s Manual for Assessing Safety Hardware (MASH), released in the spring of 2016, serves as an updated replacement for NCHRP Report 350. At a high level, MASH provides “uniform guidelines for crash testing permanent and temporary highway safety features and recommends evaluation criteria to assess test results.” Beyond expanding on the testing requirements of NCHRP 350, MASH also provides guidance on when MASH-tested and approved attenuators must be used on TMA trucks.
KEY DIFFERENCES FROM NCHRP 350?
Compared to NCHRP Report 350, MASH introduces several changes that make testing stricter and more challenging for attenuators. To understand these differences, we first look at the original NCHRP 350 tests.
Test level 2: Mandatory
- Test 50: The first mandatory test done was set to, “to evaluate risks to occupants of a small car impacting the TMA.” An 820C vehicle weighing 816 kg / 1,800 lbs struck the TMA at 70 km/h (≈ 43.5 mph).
- Test 51: Same scenario but with a 2000P pickup truck weighing 4,400 lbs.
Optional tests in NCHRP 350
The NCHRP Report 350, also listed two optional tests for a TMA to undertake. The report even says that, “Tests 52 and 53 are new tests and there is no assurance that current TMA designs can meet requirements of these tests. Moreover, there is no assurance that new TMA designs can be made to meet these test requirements without significant increases in cost or without detrimental effects on truck handling, TMA durability, or other operational considerations.”
- Test 52: 2000P pickup strikes the TMA offset from center.
- Test 53: 2000P pickup hits the center of the TMA at a 10-degree angle.
Test level 3: Mandatory if the attenuator is being certified for TL-3 performance
It involves the same tests as Test Level 2 (the basic level) but conducted at a higher speed of 100 km/h (≈ 62 mph), while applying the same evaluation criteria.
THE CRITERIA
All the tests were judged on the same criteria, including:
- “Acceptable test article performance may be by redirection, controlled penetration, or controlled stopping of the vehicle”
- “Detached elements, fragments or other debris from the test article should not penetrate the occu pant compartment, or present an undue hazard to other traffic, pedestrians, or personnel in a work zone.”
- “The vehicle should remain upright during and after collision although moderate roll, pitching and yawing are acceptable.”
- “After collision it is preferable that the vehicle’s trajectory not intrude into adjacent traffic lanes”
- “Fully assembled BLADE-TMA attenuators shipped and easy to install using the truck bracket, no additional assembly (labor) costs!”
CHANGES INTRODUCED BY MASH
At the time these tests were created (1993), they were considered adequate for evaluating TMAs, but they are now outdated compared to modern vehicle and traffic conditions.
Now that we know what exactly the NCHRP 350 tests for truck mounted attenuators entailed, we can examine the changes that the MASH testing made.
First change: Heavier impact vehicles
- Small car: 820C has been increased to a 1100C vehicle (1,097 kg / 2,420 lbs)
- Pickup truck: 2000P has been increaed to a 2270P vehicle (2,268 kg / 5,000 lbs)
These changes were made to reflect the increased weight of new passenger vehicles on the market today compared to when the tests were originally created. With the evaluation criteria remaining the same, a heavier impact vehicle makes passing the tests a much more difficult task.
Second change: Mandatory Tests 52 & 53
- Unlike NCHRP 350, these previously optional tests are now required.
- This ensures the TMA is tested under realistic crash conditions, as vehicles rarely hit the attenuator perfectly centered or straight.
In short: by making Tests 52 and 53 mandatory, the attenuator is better tested to mimic real life scenarios it will face.
PURPOSE OF MASH TESTING
The changes in MASH testing aim to ensure that TMAs on the market today can withstand real-world crash scenarios commonly encountered in modern work zones. With worker safety as the top priority, a MASH-approved TMA clearly indicates that the unit is reliable and safe for deployment in active work zones.
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