Guardrail, median barriers and crash cushions: how they work and what to ask road owners
How roadside barriers are chosen, tested and repaired, and how to report damage
Safety Behind the Wheel Foundation built this guide from Federal Highway Administration (FHWA) guidance and data, the Washington State Department of Transportation (WSDOT) design manual, Insurance Institute for Highway Safety (IIHS) data and published research on roadside barriers. Every source is listed at the end.
Why roadside barriers matter
When a vehicle leaves its lane, the next thing it meets shapes the outcome. In 2024, 7,979 people died in fixed object collisions, about 20% of the 39,254 motor vehicle deaths in the United States that year [7]. Trees were the object in 3,456 of those deaths and utility poles in 910. Traffic barriers came third, with 785 deaths, or about 10% of the fixed object total [7].
That last number is not an argument against barriers. Engineers place them where the alternative is worse, such as a steep slope, a bridge pier or oncoming traffic [4, 8]. But it shows that a barrier is a real object. It must be built and kept up so that hitting it does far less harm than hitting what it protects.
Engineers call these devices roadside safety hardware. The Federal Highway Administration (FHWA) calls them the last line of defense once a driver has lost control. The group includes guardrail, crash cushions and breakaway posts [1]. FHWA reports that deaths in collisions with guardrails fell 47%, from 568 in 1980 to 302 in 2017, and credits steady improvements in engineering and design [1].
The first question: can the hazard go away?
Roadside safety decisions follow a set order of questions. The first is whether the hazard can be taken away. Could the tree be removed, the pole moved or the slope flattened? A clear zone is the flat, open strip beside the road where a driver can recover. It only helps if it is truly clear.
Barriers come next, and only when needed. The Washington State Department of Transportation (WSDOT) says a barrier should not be used unless it is likely to make a collision less severe. Its manual warns that a barrier is not guaranteed to redirect a vehicle without injury or without causing another wreck [2].
Crash cushions follow the same logic. WSDOT describes them as protection for rigid objects that cannot be removed, relocated or made breakaway [3]. A breakaway support is built to snap or bend away when struck.
That order explains what you see. A guardrail often stands where a steep slope, bridge pier, retaining wall or row of utility poles sits close to the lane [8].
Guardrail: how the rail and its end work
FHWA says a guardrail exists mainly to protect a driver who has left the road from something worse beside it. Depending on the collision, it may send the vehicle back onto the road, bring it to a stop or slow it enough to let it continue past the rail [8].
Two parts do most of the work [8]:
- The face is the long rail beside the road. It redirects the vehicle.
- The end terminal is an energy absorbing piece at the start of the run.
The end behaves differently depending on the angle of the hit. In a head on hit, the rail is pushed through the end piece and bends away from the vehicle. In an angled hit, the end can swing out of the way so the vehicle slows down behind it. FHWA says guardrail crash tests use vehicles traveling about 62 miles per hour [8].
Length and anchoring matter too. WSDOT defines length of need as how much barrier is required to cover a fixed hazard. A run that is too short leaves part of the hazard open. WSDOT also calls for an anchor at the end of a run so the rail can pull tight along its whole length [2].
Median barriers: cable, concrete and metal beam
A median is the strip between opposing lanes on a divided highway. A median barrier stops a vehicle that drifts into that strip from reaching the other side. FHWA describes median barriers as long barriers that separate opposing traffic and redirect vehicles that hit either face [4].
The risk is severe. FHWA says head on collisions cause 8% of all deaths on divided highways, and median barriers cut cross median collisions by 97% on rural four lane freeways [4]. The AASHTO Roadside Design Guide recommends them on high speed roads with a median 30 feet wide or less and more than 20,000 vehicles a day [4]. AASHTO is the national association of state transportation agencies.
The table shows the three common types.
Comparison compiled by Safety Behind the Wheel Foundation
Three common types of median barrier
| Type | How it behaves | What to weigh |
|---|---|---|
| Cable | Flexible. Cables are strung on weak steel posts [4] | Needs room to bend. Needs more frequent repair [2, 4] |
| Metal beam | Semirigid. A W beam or box beam rail sits on steel or timber posts [4] | Often needs no repair after minor hits [4] |
| Concrete | Rigid. Little to no give on impact [4] | Lower upkeep cost. Suits narrower medians [2] |
Every type gives a little when hit. WSDOT lists typical deflection, the distance a barrier moves on impact, as 6 to 10 feet for cable barrier and 5 feet for its standard beam guardrail [2].
Indiana crash data from 2008 to 2012 shows why barriers matter. Occupants who hit a barrier had lower odds of injury than those who hit a pole or rolled over. The drop ranged from 39% for a concrete median wall to 85% for a cable barrier on the near side of the median [9]. The authors favored cable over guardrail, and guardrail over concrete walls, where conditions allow [9].
Placement and slope matter. A North Carolina study found less severe outcomes when a median barrier sat farther from the road. Cable barrier on slopes between 6:1 and 10:1 went with more severe collisions than cable barrier on flatter slopes [10]. A 10:1 slope drops one foot for every ten feet across.
Crash cushions: protecting what cannot be moved
A crash cushion, also called an impact attenuator, guards a hazard that cannot be moved. FHWA gives a bridge pier as an example. The device slows the vehicle or reduces the force of the hit [1]. WSDOT says these systems either bring a vehicle gradually to a stop in a head on hit or redirect it away in a side hit [3].
Choosing one starts with speed. WSDOT tells designers to match the system to the posted speed and says a unit rated for at least 60 miles per hour will typically fit [3]. All of these systems are proprietary, meaning each is a manufacturer’s own product [11].
Upkeep is the hard part. After a head on hit, some systems must be almost entirely replaced or have key parts swapped out, such as cartridges and braking parts. Others only need a reset. The cheapest units usually do not survive one impact [3]. A unit that is crushed or out of place cannot be counted on to protect the next vehicle.
Repair crews work close to traffic. WSDOT tells designers to weigh that exposure. It lists narrow gore areas, the wedges where an exit ramp splits from the main road, among the tough spots for repair [3].
MASH: how these devices are crash tested
MASH stands for the Manual for Assessing Safety Hardware. AASHTO publishes it. It sets one standard way to crash test permanent and temporary safety devices and to score the results. It updated an older standard, NCHRP Report 350. Since January 1, 2016, changes to devices tested under the old standard need MASH testing. The 2016 edition was current when FHWA last updated its page in August 2025 [12].
The National Highway System (NHS) is the federal network of major roads. Under a joint agreement between AASHTO and FHWA, NHS contracts put out for bid after set dates may use only hardware evaluated under the 2016 MASH edition. It applies to newly installed permanent hardware and to complete replacements. The dates were staggered by device. Cable barrier, cable terminals and crash cushions came due at the end of 2018. Other devices fell between the end of 2017 and the end of 2019 [5].
Roads outside the NHS may follow other rules or the owner’s own policy, so ask which applies. FHWA also issues optional “eligibility letters” for tested devices. A state does not need one to install a device or to get federal reimbursement for it [13].
Passing MASH tests does not make a device crash proof. It performs as tested only when it suits the site and is installed correctly.
When a barrier makes things worse
Poor barrier selection can create new risks. Watch for these problems:
- Swapping one collision for another. A study of 2,049 Indiana collisions from 2003 to 2012 described barriers as swapping high risk crashes for less risky ones. It also linked barriers near the travel lanes to a higher chance of vehicles being redirected back into traffic [14].
- Riders on two wheels. In U.S. motorcycle collisions from 2004 to 2008, hitting a guardrail was about 7 times as likely to be fatal as a collision with the ground alone [15]. Hitting a tree was almost 15 times as likely [15]. A barrier was less deadly than a tree, but far from soft.
- Too little space or length. If a hazard sits inside the deflection space, or the run is too short, the vehicle can still reach it [2].
- Ends and wrong parts. In 2016, FHWA asked agencies to review their guardrail selection, installation, repair and maintenance policies. It urged system wide inventories of guardrail terminals [6]. Safety Behind the Wheel Foundation encourages every road owner to do the same.
Upkeep: what happens after a hit
A tested barrier protects only while it is intact and set up as designed. Repair needs differ by device, as the median barrier table showed. Narrow medians also leave little room to work and may require lane closures [2]. Owners differ in the details, but a sound routine after a hit looks like this:
- Record the location of the hit and the device that was struck.
- Inspect the whole run, including the end terminal and anchors, not only the visible dent.
- Decide whether to repair, reset or replace. Cushion systems differ on this point [3].
- Use the parts the maker specifies, with trained crews who follow the installation manual [6].
- Update the inventory of terminals and parts so the next inspector knows what is there [6].
Who chooses, buys and installs barriers
On public roads, the road agency decides. States handle state highways, while counties and cities handle local streets. Public barriers must be selected, designed and installed by authorized agencies and their contractors. Residents should never install or alter them.
Typical buyers include road agencies, municipalities, campuses and private road owners. Most use three channels. A traffic engineering firm designs the layout. An infrastructure supplier sells the tested system. An approved installation contractor builds it.
What you can do as a driver or resident
As a driver, you help most by staying on the road. Set your speed before curves and keep your belt on. Slow down and give room to crews working at a barrier or cushion. Our guide to roadway departure safety covers what to do if your wheels leave the pavement.
If you hit a barrier or cushion, move to safety if you can and call 911 if anyone is hurt. Then report the damage to the road owner, because a damaged device may not protect the next driver [3].
To ask for a review of a barrier near you, follow these steps.
- Find the road owner. It may be the state, a county, a city, a campus or a private owner. Public works or 311 can point you to the right office.
- Note the exact spot: road name, nearest cross street, mile marker and direction. Take photos from a safe place. Never stand on the road.
- Describe what you see, such as a bent rail, a missing end piece, a loose cable or a crushed cushion.
- Ask specific questions. Is the device MASH tested? When was it last inspected? Is a repair scheduled?
- If collisions keep happening there, ask for a road safety review. Local crash data can help you make the case.
- Follow up in writing and keep a copy.
Frequently asked questions
What is the difference between a guardrail and a crash cushion?
A guardrail is a long barrier beside the road that shields a driver from a hazard behind it [8]. A crash cushion sits in front of a single hard object, such as a bridge pier, and slows the vehicle or reduces the force of the hit [1].
Are cable barriers safe?
A cable barrier is a flexible system that catches a vehicle and slows it down. In Indiana data, a near side cable barrier was linked to the largest drop in injury odds among the types studied [9]. Placement matters, though, and cable barrier needs more frequent repair [4, 10].
Can a barrier be more dangerous than no barrier?
Yes, if it is chosen or placed badly. Engineers use a barrier only when it is likely to lower collision severity compared with the hazard behind it [2]. A barrier that is too short, too close to a hazard, damaged or poorly installed can fail that test.
Do older barriers have to be replaced to meet MASH?
The federal agreement covers newly installed hardware and complete replacements on the National Highway System [5]. WSDOT says older crash cushions that still work fully may stay on the road and be repaired when needed [3]. So older hardware may remain on some roads. Ask the owner how it tracks and upgrades it.
Who fixes a damaged barrier, and can my neighborhood group install one?
The road owner fixes it. That is usually the state, county or city, or the owner of a private road or campus. A neighborhood group cannot install a barrier on a public road. It can report the exact location and ask the agency for a review. On private land, the owner should hire a traffic engineering firm and an approved contractor.
The bottom line
Recommendation from Safety Behind the Wheel Foundation
Safety Behind the Wheel Foundation urges road owners to remove or move a roadside hazard first, and to choose, install and repair every barrier with care. Guardrail, median barriers and crash cushions are the last line of defense after a vehicle leaves the road. They work best when engineers first ask whether the hazard can go away. Then they choose a MASH tested device that suits the site. They install it as the maker specifies and repair it fast after each hit.
You can help. Report damage, ask the road owner clear questions and bring local crash data to any review request. A well chosen, well kept barrier can turn a deadly wreck into one a family can recover from.
Related articles
- Roadway departure safety: curves, drop offs and how to recover safely
- Safer road design: a field guide to the safety fixes on your street
- Safe System approach: how road design protects you from human mistakes
- Rural road safety: why country roads are deadlier and how to drive them
- Local crash data and safety maps: how to find and read your area's data
Sources and further reading
- 1Federal Highway Administration (FHWA). Roadside Safety Hardware: The Last Line of Defense (fact sheet FHWA-SA-19-003). Undated fact sheet. Data year: 1980 and 2017 (guardrail death comparison). highways.dot.gov/media/13756
- 2Washington State Department of Transportation (WSDOT). Design Manual M 22-01.23, Chapter 1610: Traffic Barriers. Revised September 2024. wsdot.wa.gov/…/1610.pdf
- 3Washington State Department of Transportation (WSDOT). Design Manual M 22-01.23, Chapter 1620: Impact Attenuator Systems. Revised September 2024. wsdot.wa.gov/…/1620.pdf
- 4Federal Highway Administration (FHWA). Proven Safety Countermeasures: Median Barriers. No date shown on the page; opened October 2026. Data year: not stated on the page (the 97% figure refers to rural four-lane freeways). highways.dot.gov/…/median-barriers
- 5AASHTO and Federal Highway Administration (FHWA). AASHTO/FHWA Joint Implementation Agreement for Manual for Assessing Safety Hardware. 2016. highways.dot.gov/media/13516
- 6Federal Highway Administration (FHWA), Office of Safety Technologies. Memorandum: ACTION: Guardrail Terminal Installations and Repairs. November 30, 2016. highways.dot.gov/media/13571
- 7Insurance Institute for Highway Safety (IIHS). Fatality Facts 2024: Collisions with fixed objects and animals. Posted June 2026. Data year: 2024. iihs.org/…/collisions-with-fixed-objects-and-anim…
- 8Federal Highway Administration (FHWA). Guardrail 101. Updated August 11, 2020. highways.dot.gov/…/guardrail-101
- 9Zou Y, Tarko AP, Chen E, Romero MA. Effectiveness of cable barriers, guardrails, and concrete barrier walls in reducing the risk of injury. Accident Analysis and Prevention 72:55-65. Published July 2014. Data year: 2008 to 2012 (Indiana crashes). pubmed.ncbi.nlm.nih.gov/25003970
- 10Hu W, Donnell ET. Median barrier crash severity: some new insights. Accident Analysis and Prevention 42(6):1697-1704. Published 2010. Data year: five years of North Carolina rural divided highway crashes (years not stated in the abstract). pubmed.ncbi.nlm.nih.gov/20728619
- 11Washington State Department of Transportation (WSDOT). Roadside safety. Updated May 26, 2026. wsdot.wa.gov/…/roadside-safety
- 12Federal Highway Administration (FHWA). AASHTO Guidance (Manual for Assessing Safety Hardware and Roadside Design Guide). Updated August 6, 2025. highways.dot.gov/…/aashto-guidance
- 13Federal Highway Administration (FHWA). Federal-aid Reimbursement Eligibility Process. Updated February 10, 2026. highways.dot.gov/…/federal-aid-reimbursement-eligibility-…
- 14Zou Y, Tarko AP. An insight into the performance of road barriers – redistribution of barrier-relevant crashes. Accident Analysis and Prevention 96:152-161. Published 2016. Data year: 2003 to 2012 (Indiana crashes). pubmed.ncbi.nlm.nih.gov/27529451
- 15Daniello A, Gabler HC. Fatality risk in motorcycle collisions with roadside objects in the United States. Accident Analysis and Prevention 43(3):1167-1170. Published 2011. Data year: 2004 to 2008. pubmed.ncbi.nlm.nih.gov/21376915
This article reflects the safety priorities of roadside safety hardware and forgiving roadside design. It is general education, not legal, medical, insurance or design advice. Standards change, so verify details with official sources. For a specific road, contact the agency that owns it, such as your state transportation department, county road office, city public works or campus facilities office. For injuries or claims, talk with a medical professional or your insurer. Reviewed October 2026.
Cite this article: Safety Behind the Wheel Foundation. “Guardrail, median barriers and crash cushions: how they work and what to ask road owners.” drivewithcare.org, https://drivewithcare.org/guardrail-median-barriers-crash-cushions-explained/. Reviewed October 2026.
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