THE SAFETY EDGE
What Is the Safety Edge?
The Safety Edge is a simple but highly effective solution to reduce crashes on roadways. Shaping the edge of the pavement to 30 degrees minimizes the problem of vertical drop-off. This angle provides a safer roadway edge that allows drivers to re-enter the paved road safely. The Safety Edge also improves pavement density, which makes the edge durable.
Drop-offs are a safety challenge
Safety Edge can mitigate shoulder drop-off
Safety Edge can increase pavement edge durability
The Safety Edge
The purpose of this overview is to introduce the purpose and need for the Safety Edge; the practical solution the Safety Edge provides; and the features and benefits. This presentation also is an opportunity to answer questions and discuss the advantages of the Safety Edge.
Three messages are key to communicating the benefits of the Safety Edge. The Safety Edge—
- Saves lives.
- Is low cost.
- Improves durability.
This Safety Edge Technical Overview contains the following:
- Purpose and Need
- A Practical Solution
This is your elevator speech to all your partners. The Safety Edge-
- Reduces crashes and saves lives by mitigating pavement edge drop-off
- Is a low cost, systematic improvement applied during paving
- Improves durability by reducing edge raveling
Communicate that the Safety Edge is a simple but extremely effective solution that can help save lives by allowing drivers who drift off highways to return to the road safely. The FHWA's goal is to accelerate the use of the Safety Edge technology, working with States to develop specifications and adopt this pavement edge treatment as a standard practice on all new and resurfacing pavement projects.
Stress that conventional paving leaves a near vertical edge that research has shown to be more difficult to traverse by a tire than a 30-35 degree Safety Edge.
Indications from multiple recent field demonstration projects as well as a 6-7 year in-place safety edge project indicate that the Safety Edge produces a more durable outside edge to the pavement.
The Safety Edge: Purpose and Need
Safety Edge Installation: Iowa
Purpose and Need
- Crash Types and Problem Locations
- Risk Factors in Edge Drop-off Crashes
2009 Fatal Crashes (Based on FARS)
Note: Pie chart needs to be modified to reflect 2009 data. The actual numbers (18,807 & 33,808) have been updated to 2009 FARS data.
Based on the new FHWA Roadway Departure criteria that was developed alongside the new definition, the 2008 data in National Highway Traffic Safety Administration’s (NHTSA) Fatal Analysis Reporting System (FARS) indicates 52% of fatal traffic crashes can be attributed to roadway departures—17,818 fatal crashes resulting in 19,794 people killed. These are crashes in which the first event involves a vehicle running off the roadway. These are typical crashes where the pavement edge may be involved as a factor in the crash. Roadway departure crashes designated crossovers (crossing the centerline or the median) are also considered roadway departures and could potentially involve a pavement edge.
With such a significant number, if we can achieve notable reductions in roadway departure fatalities, we can significantly impact the total number of annual fatalities. Although we don’t have specific information on the number of non-fatal injury crashes that involve roadway departures, we can safely assume the cost there is also significant.
1 ROR Fatality Every 29 minutes
50 people will die in a roadway departure crash in the United States today.
How many related to drop-offs?
The AASHTO Strategic Highway Safety Plan includes an initiative to “minimize the consequences of leaving the road”. Similarly, FHWA has an initiative to reduce roadway departure fatalities. In 2008, 55% of all fatal crashed happened on rural-undivided highways. A Georgia Tech study noted 56% of fatalities had edge rutting on rural roadways. North Carolina noted 47% of fatalities had edge rutting on rural roadways.
2006 AAA Drop-Off Study
(On rural paved roads with unpaved shoulders)
- Drop-off crashes were 17.7% of ROR crashes in Iowa
- Drop-off crashes were 24.5% of ROR crashes in Missouri
- Drop-off crashes in Iowa were four times as likely to be fatal as all rural crashes and twice as likely to be fatal as other rural ROR crashes
- Drop-off crashes in Missouri were twice as likely to be fatal as all rural crashes on similar roads
Talking points: The study used probable and possible drop-off crashes to define drop-off crashes. In Iowa 5.8% of drop-off crashes were fatal where 3% of other ROR crashes were fatal (i.e., twice).
Are Drop-Offs a Problem?
This section of pavement was the site of a terrible crash. As you can see in the far background, there are sports field lights from a local High School. As reported in the Atlanta Journal Constitution, the morning of March 2003 a group of four high school students were on their way to school, their vehicle left the roadway at this horizontal curve. On re-entry the vehicle went into the opposing lane, colliding with a school bus.
Three teens died in a crash where this drop-off may have been a contributing factor. The decision on whether the drop-off was a contributing factor is a case for the courts to decide. What we do know is that crashes associated with edge drop-offs are some of the most severe (i.e., head on collisions, roll over, opposite-direction sideswipe or the driver may run off the road again and crash into a roadside object).
Background: Excerpt from article, The Low-Cost Dropoff Solution, published in Public Roads magazine, September/October 2007.
Four teenage boys from a high school in Clayton County, GA, were driving to school on a rural two-lane highway on a March morning in 2003 when something went terribly wrong.
About a quarter-mile from campus, the car's right tires slipped off the pavement and dropped onto the sandy shoulder. While attempting to return to the pavement, the 16 year-old driver overcorrected and lost control. The compact sedan crossed the centerline and slammed head-on into a school bus coming in the opposite direction. The driver and one passenger were pronounced dead at the scene; another passenger died later at the hospital. The fourth teenager was seriously injured but eventually recovered. The driver of the school bus, which was carrying no passengers, suffered only minor injuries.
One cause of the crash, according to the police report, involved a condition known as pavement edge dropoff (PEDO), the uneven edge or vertical dropoff between the paved travel lane and the unpaved shoulder. Highway safety experts consider a dropoff of 12.7 centimeters (5 inches) or more to be unsafe, especially if the edge is at a 90-degree angle to the shoulder surface. A dropoff of 5.1 centimeters (2 inches) or more is considered a potential driving hazard. The dropoff along the stretch of highway where the teens’ car slipped off the pavement ranged from about 5.1 to 10.2 centimeters (2 to 4 inches), according to two safety engineers from the Federal Highway Administration (FHWA) who visited the site the day after the crash.
When a vehicle slips off the pavement and onto an unpaved shoulder, the steep edge can make it difficult "This is likely what happened in the Lovejoy High School crash," says FHWA Safety Engineer Frank Julian, who visited and took photographs of the crash site and learned that there was evidence of scrubbing on the inside edge of the vehicle’s right tires. According to the police report, skid marks were found coming back onto the roadway, leading the inspectors to believe that "overcorrection played a role in the [crash]."
Typical Drop-Off Crash with Tire Scrubbing
Without a Safety Edge
With a Safety Edge
The Safety Edge:
The Practical Solution
Approach to Reducing
Roadway Departure Crashes
Safety Edge Installation: Georgia
- Low-Cost Solutions
- Highly-Effective Countermeasures
- Systematic Application
67% of all fatal roadway departure crashes occur on rural highways, most of them on 2-lane roads.
This is the type of roadway where the Safety Edge can have the most benefit.
The Safety Edge is a solution to a problem that can occur on almost any roadway, which can be incorporated into our systems as we pave and repave the roadways at very little cost. As you’ll see in the following presentation, there are both safety and pavement longevity benefits to be gained with this low-cost improvement.
The Safety Edge can and should be applied to other roadway types (divided and pavement with paved shoulders, and urban roads without curbs), but these type of pavements are the most critical in terms of potential fatality reduction.
Maine Non-Safety Edge Control Section
Looking more closely at the section where the Safety Edge shoe was not used on the project (about 100 feet from the location shown on the previous photo), note the crack in the edge highlighted by the pen sticking in it. The asphalt beyond the crack will break off and be wasted.
Safety Edge Installation: Georgia
Six years after this Safety Edge installation, the shape is still in ‘Like New’ condition.
The control section without the safety edge has raveled to a near vertical edge (Shape B in previous graph).
Notice the cracking that is beginning to develop near the edge on the section w/o the safety edge.
These are the locations where there were edge drop-offs noted in the preconstruction evaluation.
Even though these shoulders were pulled back flush with the pavement the drop-offs re-emerged after just one year. Can you guess why??
These Locations were both in full shade during most of the day and grass did not re-establish.