Sun Glare Dangers
Photo by Ralph Bouwmeester
In the April 1, 2010, edition of the Omaha World-Herald, staff writer Nancy Gaarder spoke of the early morning sun blinding those driving to work at this time of year. To read the World-Herald article, click here. For similar articles on this topic, see our Site Map.
During a telephone interview with Ms. Gaarder, we were asked to explain why sun glare is such a problem at this time of year in so many cities. There are several reasons.
The sun rises and
sets in line with
Since the sun rises and sets in an east-west direction at the beginning of spring and fall (around March 21 and September 21), and given the east-west / north-south orientation of street grids in so many cities, the sun just so happens to rise and set in line with east-west streets at those times of year. After the change to Daylight Saving Time on the second Sunday in March, sunrise occurs one hour later, namely, around 7:30 a.m. CDT or so in the Omaha area, that is, during the thick of the morning rush.
While the spring and fall present challenges for drivers on east-west streets at sunrise and sunset, other street directions will be equally challenging at other times of year. Note that in Omaha the sun rises and sets more or less northeast and northwest during summer, and southeast and southwest during winter. Drivers should always make themselves aware of where the sun is or where it might be as they round a curve or crest a hill.
Living west of
your place of work means
In cities such as Omaha where a large number of commuters live west of downtown, "a significant number of commuters are driving directly into the sun" during the morning commute in spring and fall. And the evening commute home can be equally dangerous.
Cooler temps mean less haze and brighter sun
Another factor that adds to the intensity of the sun's glare during spring and fall is that temperatures are generally cooler resulting in an atmosphere that is less humid and hazy.
First and last hour of daylight most dangerous
Sun glare seems to be most problematic for drivers during the first and last hour or so of daylight. At least this appears to be the trend in traffic accident cases we have been involved with. There are exceptions - in fact, visibility can be compromised anytime the sun is shining and particularly when it lies within the field of view of one's windshield. Generally speaking, the closer the sun gets to one's line of sight to an object, say another vehicle or a pedestrian, traffic light or stop sign, the more difficult it will be to detect the object. But it should also be noted that sun glare is not only a problem when the sun lies ahead - traffic signals and brake lights can be "washed out" when it shines from behind.
Be especially cautious when the sun is behind you
A special word of caution to drivers and pedestrians alike - if you see your shadow or the shadow of your car straight ahead of you in the road, you should assume that oncoming drivers are having difficulty seeing you. In other words, be extra cautious when the sun is behind your back and your shadow points toward an oncoming vehicle. Pedestrians can be fooled when the front of an approaching vehicle is lit up brightly by the sun - however, chances are the driver cannot see you very well. Be aware and be safe - assume they cannot see you at all!
Ralph Bouwmeester, P. Eng.
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