Toll booth clocks [LWN.net]

Toll booth clocks

Posted Jun 12, 2008 6:25 UTC (Thu) by man_ls (subscriber, #15091)
In reply to: Unfortunately it's for real by oak
Parent article: Stallman attacks Oyster's 'unethical' use of Linux (ZDNet)

I believe keeping the clocks in sync is the worst practical problem. Radar detectors have to be certified by an authority that they are in working order. Certifying that toll booth clocks are accurate to a certain extent (in the order of tens of seconds) could be quite expensive. Regular use of e.g. NTP would synchronize the clock, but it would not certify it.

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Toll booth clocks

Posted Jun 12, 2008 19:20 UTC (Thu) by aegl (subscriber, #37581) [Link]

My son got a ticket from a traffic cop with a radar gun. Two days later he got a letter in the mail saying that the ticket had been canceled because the radar gun used had failed its end-of-day accuracy check.

I think that it would be relatively simple to certify that the clocks are synced in a way that would satisfy a court. Just have a cop visit each machine at the beginning and end of each day, check each toll booth clock against a reference clock and then sign-off that the clocks showed the same time. If someone fights the ticket on the grounds that the clocks were not accurate, then the cop gets hauled into court to testify that (s)he personally witnessed that the clocks were working correctly on the date of the alleged offense.

Toll booth clocks

Posted Jun 12, 2008 20:29 UTC (Thu) by man_ls (subscriber, #15091) [Link]

A bit too labor-intensive, and subject to manipulation. An automatic mechanism would be more efficient... like an NTP log showing how automatic synchronizations did not drift more than a few milliseconds apart. But you probably don't want the defense to make you bring an expert witness every time someone fights a ticket -- hence some kind of certification process would be a good idea.

Too much effort, maybe. This mechanism would only catch a percentage of speedy drivers anyway: those who only speed occasionally would come out clean. Radars (and their instant speed measurement) seem to be more immediate and practical, even if their inner workings are wonderfully complex.