Guiderail
Impact Attenuators
Crash cushions installed ahead of fixed hazards to absorb impact energy, across New York, New Jersey, Pennsylvania, Delaware & Maryland.
Overview
Impact attenuators — also called crash cushions — are engineered systems installed directly in front of a fixed roadside hazard that cannot practically be removed or shielded any other way: a bridge pier, a gore-area sign structure, an overpass column, or the blunt end of a barrier run itself. Rather than redirecting a vehicle the way guiderail does, an attenuator is designed to collapse and absorb the vehicle's energy in a controlled way, cushioning the impact and reducing the severity of a crash that would otherwise be a direct hit on a rigid object.
Attenuators come in several designs — some using crushable modules, others using sand- or water-filled barrels, and others using a combination of a sacrificial nose and internal energy-absorbing elements — but they share the same underlying purpose. Selecting the right type and length for a given site depends on the approach speed, the available space ahead of the hazard, and the shape of the hazard being shielded.
Selecting the right attenuator for a given site is a function of approach speed, the width and shape of the hazard being shielded, and the space available ahead of it — a unit sized for a low-speed local road application won't provide adequate protection on a higher-speed highway approach, and a hazard with a narrow profile may call for a different system than a wide bridge pier or a full-width barrier end. Getting that selection right during design, before installation ever begins, is as important to the system performing correctly as the installation itself.
How & Why It’s Used
Attenuators are specified at the specific pinch points on a highway where a fixed hazard sits close enough to the travel lane that a runoff-road vehicle could strike it directly — gore areas where an exit ramp splits from the mainline, bridge piers in a median or along a shoulder, and the blunt ends of guiderail or concrete barrier runs where a vehicle could otherwise hit the barrier end-on. Our crews install new attenuator systems to the manufacturer's specification and the project's engineering plans.
Like guiderail, attenuators are designed to be hit — that is their job — and a unit that has absorbed an impact needs prompt inspection and, in most cases, replacement of the crushed or damaged modules before the site is protected again. Rapid post-crash attenuator replacement is a routine, time-sensitive part of our work on DOT maintenance and repair contracts, since a damaged or missing attenuator leaves a fixed hazard unprotected.
Typical Applications
- —Gore-area protection where exit ramps diverge from the mainline
- —Bridge pier and overpass column shielding in medians and along shoulders
- —Blunt-end protection at the terminal ends of guiderail and concrete barrier runs
- —Toll plaza and gantry approach protection
- —Post-crash attenuator replacement and module repair
- —New attenuator installation as part of highway safety improvement and widening projects
Frequently Asked Questions
Guiderail is designed to redirect a vehicle back toward the travel lane. An attenuator is designed to absorb and dissipate the vehicle's energy through controlled collapse, cushioning a more direct impact at a fixed hazard that cannot be shielded by a redirective barrier alone.
Common locations include gore areas at exit ramps, bridge piers and overpass columns, and the blunt ends of guiderail or concrete barrier runs — anywhere a fixed hazard sits close enough to the road to be struck directly.
In most cases, yes — the crushable or sacrificial elements that absorb the impact are generally consumed in the process, so prompt inspection and replacement is standard practice to keep the hazard protected.
We treat attenuator replacement as time-sensitive work, since a damaged unit leaves a fixed hazard exposed, and we prioritize getting a site back to protected condition promptly under our DOT maintenance and repair contracts.
Selection is typically driven by the project's engineering design based on approach speed, hazard geometry, and available space, and our crews install to that specification rather than substituting a different system on site.
In some cases, yes — if an approach speed or hazard configuration changes due to a roadway redesign, an existing attenuator system may be relocated or resized rather than replaced outright, depending on the unit and the new site conditions.
Our crews document the damage with photos and measurements before beginning replacement, since that documentation is typically required for DOT maintenance records and, where applicable, insurance or at-fault recovery on the impacting vehicle.
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