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Crash Cushion

A crash cushion is an energy-absorbing barrier system designed to decelerate an errant vehicle and protect occupants from collision with fixed roadway hazards such as bridge piers, barrier ends, and gore points. Also known as impact attenuators or fixed attenuators, these devices gradually absorb kinetic energy through controlled deformation or displacement of internal materials. They are critical safety devices in work zones and permanent highway installations where hazards cannot be relocated or removed.

Modèles

TL-2 or TL-3

MASH Test Level

Marques

Fonctionnement

Crash cushions absorb impact energy through one or more mechanisms: crushable cartridges that deform permanently, sand or water-filled modules that displace upon impact, or honeycomb structures that compress in a controlled manner. When a vehicle strikes the cushion, the device decelerates the vehicle over a longer distance and time than would occur in a direct collision with the fixed object, reducing peak forces on vehicle occupants. Most systems are designed for single or limited impacts and require inspection or replacement after each collision. The cushion's length, width, and energy-absorption capacity are engineered to match the posted speed limit and approach conditions of the protected site. Some models are reusable after low-speed impacts, while high-speed collisions typically require component replacement.

Types et variantes

Sand Barrel Array: Multiple sand-filled barrels arranged in a cluster or line; simple, low-cost solution for lower-speed applications with weight-based energy absorption
Crushable Cartridge Attenuator: Uses deformable honeycomb or plastic cartridges within a frame that crush progressively during impact to dissipate energy
Water-Filled Module System: Linked modules filled with water that displace and absorb energy through fluid dynamics; often reusable after minor impacts
Steel Frame Attenuator: Rigid steel framework with energy-absorbing elements designed for redirective impacts at barrier terminals and high-speed applications
Temporary Work Zone Attenuator: Portable or trailer-mounted systems designed for quick deployment and relocation in construction zones

Spécifications clés

Spécification	Plage typique	Signification
MASH Test Level	TL-2 or TL-3	Performance rating under Manual for Assessing Safety Hardware crash testing; TL-2 for lower speeds, TL-3 for freeway speeds
Length	12–50 ft (3.7–15.2 m)	Deceleration distance required varies with test level and approach speed; longer systems accommodate higher energy
Width	4–12 ft (1.2–3.7 m)	Lateral dimension at widest point; must accommodate the hazard width plus redirection envelope
Impact Resistance	Single-use or limited reuse	Most systems require inspection and component replacement after collision; some water-filled units allow multiple low-speed impacts

Comment l'industrie le dimensionne

The industry sizes crash cushions primarily by MASH test level, which determines the crash test performance standard the device has passed. TL-2 systems protect fixed hazards on lower-speed roads (typically 45 mph design speed) and are common in urban and work zone applications. TL-3 systems are engineered for freeway-speed impacts (70 mph design speed) and protect barrier ends, bridge piers, and gore points on high-speed facilities. Selection also considers the specific hazard geometry, approach conditions, and whether the installation is temporary or permanent.

Applications

Protection of bridge piers and overhead sign supports on highways
Shielding barrier terminals and gore points at freeway interchanges
Temporary protection of construction equipment and material stockpiles in work zones
Permanent installation at toll plaza islands and median barrier ends
Shielding utility poles, signal cabinets, and other fixed roadside obstacles
Protection of temporary concrete barrier transitions and tapers

Sécurité et opération

Proper anchoring and ballasting are critical; inadequate securing can cause the cushion to displace prematurely and reduce effectiveness
Post-impact inspection protocols must be followed to assess structural integrity and determine replacement needs
Visibility enhancement with reflective sheeting and markings ensures approaching drivers can detect the protected hazard
Installation must follow manufacturer specifications and approved plans to ensure crash-tested performance is achieved in the field
Regular inspections check for displaced components, vandalism, deterioration of materials, and proper alignment with the protected hazard

Normes et certifications

AASHTO MASH · Manual for Assessing Safety Hardware: Defines crash test criteria and performance evaluation for TL-2 through TL-6 test levels used to certify impact attenuators
FHWA · Eligibility List: Federal Highway Administration maintains list of approved crash cushions eligible for use on federal-aid highway projects
MUTCD · Manual on Uniform Traffic Control Devices: Provides guidance on placement, visibility, and markings for crash cushions in work zones and permanent installations
NCHRP · Report 350 (legacy): Previous crash test standard now superseded by MASH; many existing installations were certified under NCHRP 350 criteria

Questions fréquentes

What is the difference between TL-2 and TL-3 crash cushions?

TL-2 systems are tested and certified for lower-speed roadways (typically 45 mph design speed), while TL-3 systems meet more rigorous crash test criteria for freeway-speed impacts (70 mph). TL-3 units are generally longer and more robust to absorb the higher kinetic energy of faster-moving vehicles.

Can a crash cushion be reused after an impact?

It depends on the system type and severity of impact. Water-filled and some modular systems may be reusable after low-speed impacts with minor component replacement. Crushable cartridge and sand barrel systems typically require significant repair or complete replacement after any collision that causes deformation.

How is a crash cushion different from a guardrail?

Guardrails redirect vehicles along a continuous length of roadway edge, while crash cushions are point-protection devices that decelerate vehicles through energy absorption at specific fixed hazards. Crash cushions are often installed at the ends of guardrail runs or to shield objects that cannot be protected by redirection alone.

What maintenance do crash cushions require?

Regular inspections verify proper alignment, check for vandalism or deterioration, ensure reflective markings are visible, and confirm all components remain securely fastened. After any reported or suspected impact, immediate inspection determines whether repair or replacement is necessary to restore crash-tested performance.