Vision for Safety
Vision for Safety is a Thai driving safety training program that emphasizes the importance of driver vision in decreasing road related risks. Good vision is essential for road safety. If you can't see properly, you can't drive safely. Statistics show that one driver in 14 has a vision defect that may affect his driving performance. In addition to the driver’s visual function, the media through which he sees (windshield and vehicle glazing) and the lighting condition of the subject are equally important.
Any significant loss of visual function, such as visual acuity or visual field, will diminish a person’s ability to operate a motor vehicle safely on today’s congested, high-speed roadways. A driver with a marked visual defect may fail to perceive a potentially dangerous situation altogether or may see it too late to react appropriately. A driver whose vision is impaired by opaque materials on the windscreen or other vehicle glass areas will not be able to see and react, even if his visual function is perfect.
The importance of road safety demands that the components of safe driving be understood these components are:
The interaction of these factors is complex and cannot be inferred from the evaluation of one component alone. For example, a driver with excellent visual acuity and fair mobility but impaired cognition may be unsafe, whereas one whose only impairment is moderate visual acuity may be safe. Another applicant with a combination of moderately impaired visual acuity, moderately prolonged reaction time, and moderately impaired motor ability may be unsafe. And finally, any impairment to vision caused by the glass areas of the vehicle or the lighting situation of the subject is unsafe, even if the driver possesses all of these components.
The SDE Vision for Safety program evaluates the following components of visual sensory ability to assess an individual's ability to drive safely and emphasizes the need to maintain clear windscreen and vehicle glass to protect the effectiveness of these components:
You have to be able to see clearly to drive safely. Even the simplest reactions can take 0.4 seconds. If your distance vision is poor, you may not see hazards until it's too late to react safely. The faster you travel, the less time you have to see things and react to them. Poor distance vision and excessive speed can have disastrous results.
Distance vision can also be affected by the state of your windscreen and glasses. These should be kept clean and free of dust, scratches, and opaque materials which can greatly reduce vision on bright days and at night.
The easiest parameter to test is visual acuity. In Thailand this is the only criterion applied when issuing a driver's license. However, there are no consistent data confirming that visual acuity is a valid predictor of driving ability and safety. In fact, current data indicate that factors other than visual acuity are more accurate predictors of safe driving. Glasses or contact lenses can be worn as needed to optimize visual acuity.
Corrected visual acuity standards are:
A driver’s visual acuity must at least be such that he has time to detect and to react to obstacles, pedestrians, other vehicles and signs while moving at the maximum posted speed in daylight and in darkness. Greater levels of visual acuity are required for certain types of vehicle to ensure public safety. Road signage should be designed to be easily legible at a safe distance for all drivers who meet the minimum visual acuity standard. There should be no flaws in windshield glass and it should be kept clean and free of dust, scratches, and opaque materials which can greatly reduce vision on bright days and at night.
The ability to see to both sides is important. You need to be able to see cross traffic, pedestrians, road signs, and animals at the roadside, without having to look away from the road ahead. An adequate continuous field of vision is important to safe driving. Any significant restriction in the binocular visual field can make driving dangerous. The driver should have a 120 degree continuous view along the horizontal meridian and 15 degrees above and below fixation with both eyes open and examined together. Make the best use of your side and rear view mirrors, and keep them adjusted correctly. None of this area should be blocked by opaque materials on any glass area.
There is evidence that peripheral vision plays an important role in safe driving. Studies have used a variety of definitions of visual field impairment, however, which has resulted in a lack of consensus on the breadth of visual field necessary for safe driving. A driver with a restricted visual field but excellent scanning ability, for example, may be safer than a driver with a full visual field but no neck rotation. Individuals with some degree of peripheral visual field loss who are cognizant of the parameters of their visual field may master compensatory scanning techniques sufficient to drive safely. For some peripheral visual field defects, enlarged side and rear-view mirrors may be useful. The vision for safety evaluates the extent of a driver’s peripheral vision and emphasizes the importance of maintaining both good clear visual lines and developing the scanning ability of the driver.
Useful Field of View: Visual Attention
A useful field of view (UFOV) test has been developed to access an individual’s ability to process and react in a timely fashion to multiple visual events occurring simultaneously. It defines the visual field within which rapidly presented visual material can be used. The test includes processing speed, selective attention, and divided attention. A reduction in the UFOV has been associated with increased future crash involvement, whereas a moderate reduction in visual acuity, contrast sensitivity, and visual field were not.
Because the UFOV test relies on both visual sensory and cognitive skills, it provides a more global measure of visual functional status than either sensory or cognitive tests alone. It is a good predictor of driving performance and it is better than chronological age for identifying drivers at risk for crashes.
Contrast Sensitivity and glare recovery
A new study has associated severe reduction in contrast sensitivity with increased crash risk. Drivers with reduced contrast sensitivity may benefit by limiting their driving to the hours between dawn and dusk, and some find their contrast sensitivity improved by wearing yellow filters. The SDE Vision for Safety program evaluates a driver’s visual contrast sensitivity using modern eye testing equipment and recommends that film not be applied to windshields or other glass which would reduce the driver’s contrast sensitivity.
Glare recovery is the speed and efficiency by which the pupil re-adapts to night conditions after being flooded with a sudden bright light – like that of oncoming traffic. The vision screener simulates these adverse night driving conditions with special high-intensity bulbs nestled within the testing unit.
Contrast sensitivity measures the ability to see details – in this case curbs, pedestrians, and traffic signs – in adverse driving conditions like fog, darkness and snow. The vision screener targets show images at different levels of contrast, using reflective light to mimic real world vision.
You need to be able to judge distances well to pass other vehicles and change lanes, especially in busy traffic. If you've recently lost the use of one eye you need to take extra care. You might need to stop driving for a while, until your vision has adjusted. The SDE Vision for Safety program evaluates the driver’s ability to judge depth using modern driver vision screening equipment. This equipment can test for glare and contrast sensitivity.
Accommodation (near vision focusing)
When you're driving, you need to look from the road to the dashboard and back again quite often. This ability to change focus from far to near is called accommodation or near vision focusing. Over the age of 45, most people have increasing difficulty with near vision, and may need glasses to see the dashboard instruments clearly.
You need to be able to see in low and variable light conditions, and recover quickly from the glare of oncoming headlights. Glare recovery is best in drivers under the age of 30, and night vision can deteriorate after the age of 40.
Eyes are much slower to adapt to night-time light levels after they've been exposed to bright light. Being outside in the sun for only a few hours can slow the dark adaptation process, so you might not have your normal night vision for several hours after dark. Some people find their night vision has deteriorated and they can't drive safely at night at all.
Color plays an important part in road safety. Drivers must instantly recognize traffic lights, indicator signs, hazard warning lights and stop lights, and people with color vision defects may react slower to them. Avoid using sunglasses, because they can seriously interfere with some people's ability to distinguish traffic light colors.
The visibility and protective systems of your vehicle
Automotive engineers always aim to design cars with the greatest range of visibility. They continually increase the total amount of glass area around the driver until they reach the limits of design. Windshield design is a compromise between strength and visibility. The glass must protect the driver and passengers from the environment but must not distort or block their vision. The glass must also act as a support for the steel roof of the vehicle. If it were possible designers would make the roof and supporting structure of glass or other transparent materials so as to give totally unobstructed vision lines all around the driver. Additionally, the glass must be strong enough to hold the driver and passenger inside the car in the event of an accident, but be weak enough that the occupants can be easily removed from the car by emergency workers. Automobile glass makes up a large portion of any automobile. The glass may look the same as it has for decades, but there have been subtle changes. Most of the changes involve the windshield.
Windshield (or windscreen) design is an extremely critical safety feature of any car. Glass must withstand dramatic changes in surface temperature and must be able to handle large differences in temperature on the outside versus the inside of the car. The glass must withstand internal versus external pressure differences. The glass must protect against wind, insects, and animals as well as stones and rocks hitting it at high impact speeds. In some cases, the glass must even protect against bullets. Still designers must use glass or another transparent material that permits maximum visibility and the greatest transparency. Anything that causes windshield glass to lose its transparency suddenly, such as fog, steam, rain, dust, mud, coverage by opaque material such as cloth, paper or plastic is cause for alarm. Breaking, shattering, or cracking of a windshield can cause physical damage to the driver as well as a reduction in vision.
Automobiles produced before the 1950's used flat glass for the windshields and two piece windshields were common. The first major change occurred in the 1950's with the use of curved glass. Flat sheets of glass were heated as they moved on a conveyor belt and the glass was allowed to sag into shaped over molds. Curved automobile glass is still manufactured by this method today.
Safety glass windshields have been used for decades by the manufacturers. These windshields have a tough plastic sheet bonded between two layers of glass. Today's automobiles use this type of windshield but many use a colored sheet of plastic to give the windshield a "tinted" appearance. The plastic layer holds the glass together in an accident and makes it difficult for an object to be thrown through the windshield.
Today, glass has become a structural part of the car body. All fixed or non-opening glass is glued in place to add strength to the upper body. In the past, fixed windows were installed in rubber moldings or held in place with clips and sealed with a ribbon of sticky butyl rubber. Now, urethane adhesive is used to bond the glass in place. This strong glue takes several hours to cure, so often the vehicle must sit overnight when a new windshield is installed. To prevent the urethane adhesive from breaking down under sunlight, the glass is colored black around the edges.
The glass has also become thinner. Compare a windshield from twenty years ago to a new one today and the new one will be about half as thick and weight. In the quest to lighten the automobiles and reduce vehicle weight for improved fuel economy, glass has been changed too, but the method of bonding the glass in place has made the assembly stronger than ever.
There are few options when it comes to repairing windshields. Injecting an epoxy resin into the crack can repair short cracks and large chips. The repair and the crack become almost invisible, but it can be seen if inspected carefully. Many glass shops can perform this repair, but the windshield may require replacement if the cracks are large.
Finally, windshields are expensive. Most automotive glass comes from only a few manufacturers. The windshields with the best optical clarity are used by the automobile manufacturers for new car production and replacement glass sold at dealerships. The rest of the glass goes to the aftermarket glass shops. There may be slight flaws so the glass is cheaper, but if the flaws are not obvious, then the glass is a good deal.
Side and rear windows
Side and rear windows are also a form of safety glass, but they are not laminated like the windshield. Instead, the manufacturer tempers (surface hardens) the glass after it is formed. When tempered glass breaks, it shatters into a million tiny pieces. The small pieces are sharp but not big enough to cause extremely serious injuries.
Rear windows are often equipped with electric defoggers. Some cars have electrical wipers installed to keep the rear window clean.