# Those "Readers" Over Some Interstates (Not Tolls)
**URL:** https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608
**Category:** Factual Questions
**Created:** [July 26, 2022, 6:46pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608 "2022-07-26T18:46:02Z")
**Posts on this page:** 11
**Page:** 1
### Author:  [@Jinx](https://boards.straightdope.com/u/Jinx)
#### Post date: [July 26, 2022, 6:46pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/1 "2022-07-26T18:46:03Z")
Just west to southwest of Philly runs the “Blue Route”, a 20 mile section of I-476 highway. And, maybe every 3 miles, there is some sensor centered over the highway on a cantilevered arm hung off a pole. It must be some camera or detector, but what? For what purpose. It looks like the same hardware configuration one may find near weigh scales on some highways. (I’m not sure what those really do, either.)
The latter are few and far between, The former are spaced apart in presumably even intervals along the stretch of highway. Maybe our good Philly SDopers can explain what they are? (For those unfamiliar with this route, this section is toll-free, so it is not for electronic toll collection.)
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [July 26, 2022, 7:08pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/2 "2022-07-26T19:08:21Z")
This?
> **[PrePass weigh station bypass applications and transponders](https://prepass.com/services/weigh-station-bypass-service/)**
>
> The most comprehensive and trusted weigh station bypass system available. PrePass uses transponders and applications for the most bypasses possible.
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### Author:  [@Jinx](https://boards.straightdope.com/u/Jinx)
#### Post date: [July 26, 2022, 7:15pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/3 "2022-07-26T19:15:39Z")
Well, that probably addresses that latter half of my question, But, (a) I-476 never had and still lacks weigh stations, and (b) the video at your link doesn’t show a device hanging over the road (unless I missed it)…so I can’t identify the device I am picturing.
(FYI: I hate how this Board posts “replies”.)
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### Author:  [@Voyager](https://boards.straightdope.com/u/Voyager)
#### Post date: [July 26, 2022, 8:45pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/4 "2022-07-26T20:45:41Z")
I have no idea about the Blue Route, but in California there are multiple sensors and cameras over roads to help monitor the flow of traffic, some of which are used by the morning news traffic reporters. Could it be some of them?
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### Author:  [@hocow](https://boards.straightdope.com/u/hocow)
#### Post date: [July 27, 2022, 3:40pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/5 "2022-07-27T15:40:48Z")
I frequent the Blue Route, and know exactly what you’re referring to. I have always believed those to be sensors to calculate the estimated travel time to specific points that are displayed on the traffic signs. Typically on the Blue route they display estimated travel time to Route 1, Interstate 95, and the Schuylkill Expressway. [This link](https://www.fox43.com/article/news/local/contests/electronic-message-signs-providing-travel-times-in-south-central-pennsylvania/521-198b3df1-77f3-4cf9-a21c-43114e8be36d) seems to support this theory, and provides a sample of the sign to which I’m referring.
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### Author:  [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)
#### Post date: [July 27, 2022, 3:47pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/6 "2022-07-27T15:47:29Z")
Cameras that can recognise number plates are often used to calculate time of transit and issue fines. Might be something like that.
The systems that predict travel times don’t need to use cameras necessarily. Some systems listen for bluetooth signals from whatever devices are in cars and track them by the unique ID of the device. Which is trifle scary. Those systems just need antennae over the road.
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### Author:  [@Topologist](https://boards.straightdope.com/u/Topologist)
#### Post date: [July 27, 2022, 4:21pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/7 "2022-07-27T16:21:13Z")
In the New York area, I believe the travel times are based on scanning for EZPass tags (even on non-toll roads).
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### Author:  [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)
#### Post date: [July 28, 2022, 2:28am UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/8 "2022-07-28T02:28:56Z")
> [@Topologist](#):
>
> In the New York area, I believe the travel times are based on scanning for EZPass tags (even on non-toll roads).
I am fairly certain this is what the OP is describing on the Blue Route. They are the same shape as the EZPass scanners on toll roads.
The Blue Route also has pretty accurate “time to exit x” signs, so some means of measuring flow is in place.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [July 28, 2022, 3:49am UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/9 "2022-07-28T03:49:47Z")
We’re seeing EZPass readers going up all over the major highways. This is partly the start of tolls on trucks, and everyone is sure tolls on regular passenger vehicles is sure to follow.
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### Author:  [@Jinx](https://boards.straightdope.com/u/Jinx)
#### Post date: [July 30, 2022, 2:20pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/10 "2022-07-30T14:20:34Z")
Thanks, all! Monitoring the flow of traffic n my particular experience makes the most sense. Thanks, all for your input!
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### Author:  [@Voyager](https://boards.straightdope.com/u/Voyager)
#### Post date: [July 31, 2022, 9:11pm UTC](https://boards.straightdope.com/t/those-readers-over-some-interstates-not-tolls/968608/11 "2022-07-31T21:11:51Z")
> [@TriPolar](#):
>
> We’re seeing EZPass readers going up all over the major highways. This is partly the start of tolls on trucks, and everyone is sure tolls on regular passenger vehicles is sure to follow.
In the Bay Area the HOV lanes have FastTrak readers, and those without enough people in the car can use them if they pay. (The transmitters have a switch to let you give the number of people in the car.) Signs give the price to a given exit, which changes with traffic density. We also have time to exit signs.
Back when I was commuting Google Maps gave estimated times and speeds based on location info from Android phones, but it was never very accurate. The government estimates are much better.