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Comment by threeseed | Hacker News Reader

Tailgaiting is a vague concept though. One person's idea of tailgaiting is another person's idea of maintaining a safe braking distance.

If you tried to for example leave a car's body length distance in most busy cities you would have car after car aggressively cutting in front of you. This is even more dangerous than the original tailgaiting.

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Now, I'm not saying a car's length is an appropriate distance. Generally speaking it should be 2-3 seconds. But I see this idea a lot on the internet, particularly on reddit: I should be unsafe because other people will get mad at me for being safe which will make them do wildly unsafe things.

I'm sorry, but I can't accept that. Police need to start focusing on safety instead of revenue generation. I don't care what some idiot is doing, if you're tailgating them at highway speeds in the lane next to me you're putting us all at risk just so you can get somewhere 3 minutes faster. I don't care if you're upset about the length between the car ahead of you and the one ahead of it. Cutting them off in the lane next to me and nearly causing a reck is insane. We have to stop just accepting that being an asshole is okay and start holding people accountable.

On the contrary, its unsafe to not tailgate close enough. Speed and tailgating don't kill, differences in speed kills.

If you are two seconds behind, they could come to a near stop and you can crash into them at full speed.

If you drove with zero distance between the your bumper and the car in front of you, if they brake hard you will have no impact at all.

This is why it's safe for train cars to tailgate.

In my view, autonomous cars will likely one day form trains for higher traffic density and throughput while remaining safe.

If you drove with zero distance between your bumper and the car in front of you, they will be unable to brake hard, because its trying to stop an extra ton of mass. you're fine sure, but they just ran over that kid crossing the road without looking. or just t-boned someone. and heaven forbid someone was tailgating you too.

autonomous cars can form trains because they can react orders of magnitude faster than a human can to suddenly changing driving conditions.

You seem to have taken the concept that the larger the differences in velocity the greater the damage and extrapolated more from it than you ought to have.

It's not, though.

In Germany the minimum safety distance is taught in driving classes and severe violations of it will be fined like any other reckless behaviour.

The rule of thumb is "as much of a distance as you pass within two seconds". This scales wonderfully with speed and easily covers the reaction time and breaking duration.

Sure, in urban traffic the typical safety distance is usually less than a vehicle length, but with both tailgating and cutting in on someone constituting reckless driving offences, that's not a huge problem.

It's the same in the UK.

You can also be fined for hogging lanes on a motorway, thankfully.

We also have a concept called "Richtgeschwindigkeit", a recommended maximum speed. For the Autobahn (German motorways) it's 130 km/h unless there is a speed limit lower than that. This is the speed you're expected to drive under "normal" circumstances (i.e. good weather, low to medium traffic, clear sight).

Part of driver's education is being able to adjust your speed to the conditions and safely maintain the recommended speed on the Autobahn when possible. If you are too scared to drive at such speeds or unable to do so safely, you won't pass.

Of course we still have plenty of drivers who are afraid of driving on the Autobahn (often because they don't do it regularly enough once they have the driver's license) and especially the elderly can be in denial about the limits of their actual abilities and make up for their inability to drive safely by driving more slowly (which isn't necessarily any safer).

In the UK it's not uncommon to see chevrons painted along each lane where in you're meant to keep a minimum of two chevrons from the car in front (http://www.roberthempsall.co.uk/blogimages/keep-apart-2-chev...).

Talgetting is measured in seconds as reaction time + braking distance = ~2s, whether you are on a highway or in a city. There is nothing sujective about it. Most drivers keep just enough room for the reaction time, and it works ok as long a the car ahead doesn't hit an immobile object (e.g. a log, a car, a kangaroo, a wild boar).

Fixed 1 second of braking time won't save you if the front car hits an immobile object. The correct formula would be (1 + .046 mph) seconds [0], where mph is speed in miles per hour. It evaluates to 3.76s at 60mph and at 4.9s 85. Note that 1 second of reaction time is not exactly generous: http://www.webpages.uidaho.edu/niatt_labmanual/chapters/geom... - cites times 'less than 2.5 seconds' to actual brake application.

[0] 1mph/(9.8m/s2) in seconds, according to Google, assuming friction coefficient of 1

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