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Comment by pc86 | Hacker News Reader

> At 4:27 p.m. last Wednesday, the system caught a Route 11 city bus doing 34 mph.

Which isn't even fast enough to get a ticket from local police.

In my state (which is not Virginia, and it will vary everywhere), local police are prohibited from using radar and need to use an actual stopwatch to track your speed. Obviously very error prone, and they're supposed to basically give you 10 mph leeway - meaning on that road you basically couldn't get a ticket for going under 36 mph.

Also it doesn't say what they determine speeding to be. Based on his description the vehicle should be wholly between both markers for 40 frames at exactly 25 mph. Are cars that touch the mark on frame 39/40 considered speeders since they're going ~25.025 mph? There is a reason many states do not start issuing tickets until 5, 6, 9, 10+ mph over the posted limit.

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That's ridiculous. A 35mph collision with a pedestrian would almost certainly result in a dead pedestrian. 25mph is usually survivable.[1]

A 20mph speed limit, strictly enforced would drop pedestrian fatality rates to essentially 0.[2]

1: http://humantransport.org/sidewalks/SpeedKills.htm 2: http://www.visionzeroinitiative.com/

The lowest limit in my state (aside from 15 in some parking lots) is 25. It is rare for anyone to go below 30, most are going about 35.

While getting onto a toll road in Oklahoma a few years ago, I was surprised to see a 17mph speed limit.

I saw a couple odd ones around Nashville last time I was there, I think it was 23 on a small road leading toward a mall.

In the video it looks like there's a gradient applied to the speeds. The color of the speed read out changes from a greenish yellow to red orange around what seems like 10 mph. There one that's yellow at 34 and another that's red orange at 35. They don't say if the 25-35 gets binned differently but that's not too surprising, it's a local news piece not a presentation.

Even so just because the police aren't allowed to give you a ticket because of the measurement error or uncertainty or mercy doesn't discount that they're still speeding.

I live in Va, just not that part, and the rule of thumb is anything less then 10mph over and you generally won't get a ticket. The only exception to this is places like school zones.

That's generally the same in Michigan unless it is a subdivision/residential area, but even then it's rare for a cop to waste the time. It's possible to get a ticket for going 1-5 MPH over the limit. It's described as a "we can find a reason to pull you over for what we want to pull you over for but do not have enough evidence to do so" such as you're having done something suspicious at a known drug house or someone calling about how many drinks you've had at a bar despite you not driving suspiciously. It's crap, but it's common.

Most of the time people receiving the 1-5 MPH tickets are receiving them for violating the speed well beyond that amount (with the actual clocked speed written on the ticket). This encourages people to just pay the ticket without fighting it since they've been given a much lower civil infraction and it makes it a lot harder to succeed in court since the judge knows "radar calibration/accuracy" is much less likely with the written, clocked speed.

Unless you're on 495 then it's like 20mph over and the police may still pass you....

My car can warn me if I exceed the local speed limit by more than a set amount. I had to turn it off after a while, because it was just getting annoying on 495.

It's pretty funny to drive back into the city from points west on I-66 as the speed limit drops 70-65-60-55. I usually maintain a steady 7 over and that makes me go from one of the fastest cars on the road to one of the slowest.

The guideline I was taught was <10% over on surface streets and <14mph over on controlled access (interstates, etc).

FWIW, I've never been pulled when I was following those guidelines (driving in GA + SC).

One of the rules of thumb taught to cops is "over by five, let 'em drive, over by 10, get out your pen"

The variation I always heard (as a driver, not a police officer) was, "Five, you're fine, ten, you're mine!"

Where I grew up (eastern WA): "Eight is great; nine, you're mine."

10 MPH ?

That's ridiculous, elsewhere it is 10% because that is the legal requirement of the speedometer

You're also relying on the reflexes of someone who is sitting in their car literally watching traffic for hours at a time.

The state police can use radar so the floor goes down to 6 over the limit if they are enforcing.

So now you're telling me the police check speeding by eye. Jeepers !

It's literally "start the stopwatch when the front tire hits the first line painted on the road, stop it when the front tire hits the second line (or some other predefined immobile point), and look at a chart to see how fast they're going."

Usually radioed to a second car down at the next intersection.

No wonder people think the moon landings were fake.

The 10% margin of error for a speedometer only applies in one direction: they're allowed to say you're going faster than you really are by up to 10%, but they're never allowed to say you're going slower than you really are (in England).

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