Archives

Thursday, September 20, 2012

Better safe than sorry: roadway departure crashes

Adhering to the
posted speed
limit is important.
By Kohinoor Kar and Mike Cynecki
Guest Bloggers

What is a roadway departure crash?

By definition, a roadway departure crash is a non-intersection crash that occurs after a vehicle crosses an edge line or a centerline, or otherwise leaves the traveled way.

However, not all roadway departures result in crashes. While a roadway departure incident in itself may not initially be harmful, the

secondary events or crashes resulting from the roadway departure can be deadly. 

How to avoid a roadway departure?
There may be various reasons why a vehicle departs from its lane or runs off the road. However, most times it happens due to driver error, such as speeding on a sharp curve or a steep grade (particularly on rural two-lane highways), distraction, inattention, intoxication, fatigue, nighttime visibility or vehicle issues such as tire blowouts, and some may involve roadway issues such as ponding water or icy roads. The best way to avoid a roadway departure is to always be alert, attentive and clear-headed when driving and to conduct periodic inspection and maintenance of your vehicle.

Successful measures for safe driving also include paying proper attention to the road in front of you as well as to nearby vehicles; driving at an appropriate speed for the existing roadway, traffic and weather conditions; and avoiding any kind of distraction, such as using handheld communication devices, changing a CD or radio station, setting the GPS unit while driving or engaging in intense conversations with passengers.

Approaching curves and freeway ramps
Unfortunately, many drivers approaching curve warning signs with a lower advisory speed plaque do not slow down in conformance with the advisory speed. The reason for an advisory speed is to warn the driver of a specific roadway or traffic condition recommending a need for a reduced speed. If the traffic or weather condition is not suitable for the advisory speed posted for a curve or any other roadway condition(s) on a stretch of highway, one must slow down to a reasonable speed that may even be lower than the advisory speed.

The same driving behavior is quite often observed at freeway ramps. While exiting a freeway, notice how many black tire marks are visible on the concrete barrier or ramp. It’s not necessarily the ramp design that causes drivers to run off the road. Instead, it is usually driver error that causes these impacts. Most of these crashes are due to drivers not slowing down enough prior to entering the ramp, not heeding the advisory speed or not driving consistent with the existing conditions.

Overcorrection can be deadly!
Many single-vehicle roadway departure crashes often result in serious injuries and fatalities, especially since most occur at high speeds. According to Arizona crash statistics, slightly more than 18 percent of the total crashes in 2011 were single-vehicle crashes, but these crashes accounted for more than 40 percent of the statewide fatal crashes. These numbers clearly indicate the severity of single-vehicle crashes.

Sometimes a driver is surprised by an animal that runs into the road or a vehicle that appears to be moving into their lane, which causes a reflexive action to avoid the crash. When a driver, who is travelling at a high speed and is distracted, drowsy or inattentive, runs off the road even slightly, he/she often makes an attempt to remedy the situation quickly by jerking the wheel in the opposite direction. This sudden movement of the wheel causes the car to veer to the other side, often sending the car across the roadway or causing it to roll. In fact most drivers who run off the left side of the roadway, do so after running off to the right side and overcorrecting when trying to get back onto the roadway.

To have better control of the steering wheel, you must always use both hands when driving. You will have better control of your vehicle if you think of your steering wheel as an analog clock and place your hands at the 9 and 3 o’clock (middle) positions. The 9 and 3 positions are intended to maximize the leverage on the steering wheel. Always keep both hands on the wheel. Doing so can help avoid lane departures, and if you do inadvertently run off the road, it will allow you to have better control of the steering wheel under emergency conditions. At very high speeds, depending on the roadway geometry, it may be a better option to take these steps:
  • Don’t panic. 
  • Slow down by easing off the gas pedal. 
  • Slowly apply the brakes. 
  • Safely stop on the shoulder or on the roadside as appropriate. 

The key is to bring the vehicle to a full stop rather than try to get back on the road immediately. In some cases, hitting a bush or minor objects on the roadside after an unexpected roadway departure will probably result in less of an impact and have a lower potential for serious injuries and damages.

Every roadway departure situation can be different and unique in nature. However, certain driver behaviors can save lives or prevent serious injuries and damages by always staying alert and avoiding overreaction. Preventing a roadway departure is not difficult, and common sense can help avoid life-changing incidents behind the wheel. Undoubtedly, it is always better to be safe than sorry.
-----------------------------------
Kohinoor Kar, Ph.D., P.E., PTOE, a professional engineer with 23 years of combined experience in the roadway, traffic and safety field, has been with the State of Arizona for past eight years.

Michael J. Cynecki, P.E. retired from the City of Phoenix after a career of 26 years in the Street Transportation Department, and is currently with the consulting firm of Lee Engineering, LLC.

Disclaimer: Opinions expressed in this article are those of the authors or references cited herein and may not necessarily represent the views of the agencies they are affiliated with. Information contained in this article are for general awareness only and are not intended to substitute for professional advice to any particular person or case. Some of the information might change over time in which case the current practice would supersede all previous practices.
Posted by Angela DeWelles   |  Labels:  
Back