The Light at the End of the Tunnel

James R. Schmidt, Jr., BSME, Collision Reconstruction Engineering Analyst

Okay, if it’s not speed from video that I’m writing about, then it’s sun glare!

Sun Glare 1

Sun Glare 2

Sun Glare 3

Sun Glare 4

Sun Glare 5

Recently, while heading westbound on the Pennsylvania Turnpike on the approach to Mid-County through to Valley Forge, there it was … sun glare!

This sequence of images shows the forward-facing view relative to the direction of travel over a 6-minute period in the ~15 minutes prior to sunset. While these images hardly do it justice, it was the in-your-face kind of sun glare, with one exception: some clouds on the horizon, in the otherwise clear sky, that eased the severity of the glare…a bit.

The exact positioning of the sun at the precise time and location of each image was researched and plotted on an aerial photograph.

aerial photograph

As an example, the researched sun position along with a closer view of the corresponding plot for the middle of the five image locations is shown below:

Sun Position

aerial photograph
As you can see, the alignment of the sun (i.e. the yellow line on the aerial photograph above) relative to the roadway at that location is nearly head-on (i.e. in-your-face).

Over the course of these five images, the altitude of the sun decreased from 2.7 degrees to 1.6 degrees, and its position was within about 6 degrees of straight ahead (some closer to straight ahead than others). While there are other factors that may contribute to determining whether there’s a sun glare situation (i.e. fix objects, roadway grade, cloud cover, windshield conditions inside and outside, etc.), the low altitude of the sun and its close alignment with the roadway, as shown in these images, are required for a “true” sun glare situation.

James R. Schmidt, Jr., BSME, Collision Reconstruction Engineering Analyst with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.

 

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