# Flashing Hignbeams at Streetlights

**URL:** <https://boards.straightdope.com/t/flashing-hignbeams-at-streetlights/234428>\
**Category:** Factual Questions\
**Created:** [March 15, 2004, 2:56pm UTC](https://boards.straightdope.com/t/flashing-hignbeams-at-streetlights/234428 "2004-03-15T14:56:22Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Stupendous\_man](https://avatars.discourse-cdn.com/v4/letter/s/a8b319/32.png) [@Stupendous\_man](https://boards.straightdope.com/u/Stupendous_man)\
**Post date:** [March 15, 2004, 2:56pm UTC](https://boards.straightdope.com/t/flashing-hignbeams-at-streetlights/234428/1 "2004-03-15T14:56:22Z")

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I’ve seen many people do this as they approach a red light at an intersection. The apparant logic behind it is that emergency vehicles with flashing lights approaching an intersection will cause a sensor to activate and change the light to green in their direction, thus eliminating the need to cut through opposing traffic. However, I remain skeptical, given that I have never seen a sensor, nor have I noticed the flashing light trick be successful. What I do see often is police, fire, and ambulance vehicles cutting through opposing traffic carefully, with no lights changing other than is normal for their timing.

Do these sensors exist? If so, can automobile headlights be flashed to activate them?

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**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\
**Post date:** [March 15, 2004, 3:07pm UTC](https://boards.straightdope.com/t/flashing-hignbeams-at-streetlights/234428/2 "2004-03-15T15:07:04Z")

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Yes, they do exist, but [drivers’ high beams can’t affect traffic light sensors](http://www.defrance.org/artman/publish/article_484.shtml)

> [@](#):
>
> [A]ccording to Pennsylvania Department of Transportation officials… you’d have to flash your headlights 14 times per second to activate the pre-emption receivers that are controlled by strobes.

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**Author:** ![Stupendous\_man](https://avatars.discourse-cdn.com/v4/letter/s/a8b319/32.png) [@Stupendous\_man](https://boards.straightdope.com/u/Stupendous_man)\
**Post date:** [March 15, 2004, 3:09pm UTC](https://boards.straightdope.com/t/flashing-hignbeams-at-streetlights/234428/3 "2004-03-15T15:09:51Z")

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Excellent. Thanks for the response.

Thread can now be closed at mod’s discretion.