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Comment by logfromblammo | Hacker News Reader

Change that to median roadway speed, and I'll be on board. Speed limits are too often set by clueless folk for political concerns, rather than by traffic engineers for maximum throughput for a given safety factor.

There should be some allowance for ensuring that the median speeds of adjacent lanes have a good range separation. I can't even count how many times I have seen a tractor-trailer in the left lane at 70 mph passing a tractor-trailer in the right lane at 69 mph, as passenger cars stack up behind them. It creates a dangerous situation that I can only avoid by slowing down or exiting the roadway.

Speed limits should apply only to the rightmost lane, and additional lanes should be between 5 and 15 mph faster than the current speed of traffic in the lane to their right, regardless of their absolute speed. It makes sense, and it would improve traffic flow, but it can't become law because it would be too complicated for cops to enforce.

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> I can't even count how many times I have seen a tractor-trailer in the left lane at 70 mph passing a tractor-trailer in the right lane at 69 mph, as passenger cars stack up behind them. It creates a dangerous situation that I can only avoid by slowing down or exiting the roadway.

Presuming the max speed was 70mph, your post epitomizes the real danger. Traffic should not stack up behind vehicles traveling at the maximum allowed speed. Or at least, it should not stack up in a dangerous way. Twenty vehicles stacked up at proper following distances, all traveling 70mph, is actually optimal. Yet you seem to disparage it. You will never achieve optimal traffic flow if the general attitude toward actual optimal patterns is disdain.

If the max speed limit was above 70mph, ignore the preceding paragraph.

> proper following distances, all traveling 70mph

Hi. Welcome to Earth. It looks like you missed orientation.

Humans drive at different speeds, and usually follow too closely. We have recognized this species-wide problem, and are currently trying to build driving robots that will reduce the impact. Until they are ready, every collision you may see on the road was likely caused by a human driving non-optimally.

Therefore, rational drivers must presume that the other vehicles on the road may possibly behave irrationally, and therefore must introduce a safety margin for the incorrect behavior of other drivers in addition to the margin defined by their own capabilities.

Show me a train of 20 cars moving at 70 mph with less than 1 second of separation between them, and I'm just going to ease off the accelerator, and maybe look for my next rest stop, until those lunatics are far enough ahead that I'll possibly learn about their 6-vehicle pile-up early enough to detour around it. The only way that is optimal is if there are zero humans in it.

"Proper following distances" absolutely does not mean "with less than 1 second of separation between them"!

"Proper following distances" means "you can react and stop in time to prevent a collision if the car in front of you brakes very hard".

Ripped from a wiki article on the topic:

The United States National Safety Council suggests that a three-second rule—with increases of one second per factor of driving difficulty—is more appropriate. Factors that make driving more difficult include poor lighting conditions (dawn and dusk are the most common); inclement weather (ice, rain, snow, fog, etc.), adverse traffic mix (heavy vehicles, slow vehicles, impaired drivers, pedestrians, bicyclists, etc.), and personal condition (fatigue, sleepiness, drug-related loss of response time, distracting thoughts, etc.). For example, a fatigued driver piloting a car in rainy weather at dusk would do well to observe a six-second following distance, rather than the basic three-second gap."

I am describing what people actually do, not what they should do. I think everybody knows that they shouldn't tailgate, but they just do it anyway, because "F U get out of my way".

Welcome to the 21st century. Times have changed. Driving robots are now a reality. Adaptive cruise is a real thing, and the most well-known adaptive cruise systems slow down to adjust to traffic speeds, not speed up and pass.

In fact, the most well known system made an adjustment some time ago that it would no longer exceed the legal speed limit.

> rational drivers must presume that the other vehicles on the road may possibly behave irrationally, and therefore must introduce a safety margin for the incorrect behavior of other drivers in addition to the margin defined by their own capabilities.

Exactly. So slow down. Join the train of cars instead of trying to pass them. Maintain a safe distance and don't worry that you will be late. You won't. 20 cars driving 70mph is better than 10 cars driving 80, one driving 85, five driving 75, two driving 90, and two driving 70. It is better for all of those cars, not just the two driving 70. They will all be safer, and they will all arrive at their destinations within 60 seconds of when they would have.

Humans are not machines, of course. But they can work on one important attribute with which every automated vehicle should be programmed: patience. In a world where human drivers increasingly share the road with robots, human patience must adapt.

> because it would be too complicated for cops to enforce.

The only reason speed limits get so much focus is that they are so easy to enforce.

Because of that, they have essentially become a direct-to-police tax, rather than something useful.

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