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Comment by robertlagrant | Hacker News Reader

Of course it's pragmatic. Free-flowing traffic at 50mph beats people zooming up to 70mph then braking, then zooming again. Freeflowing traffic at 50mph annihilates traffic from accidents.

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Traffic is rarely “free flowing” at any speed on these kinds of roads. Often I see “moving roadblocks”: clumps of cars going around or just under the speed limit jockeying around each other, impeding other traffic from moving around them. So-called “defensive drivers” are often unpredictably overly cautious: I’d wager they are at least an indirect cause of accidents quite often, but are severely under-represented in the statistics (if/when they’re represented at all).

> Often I see “moving roadblocks”: clumps of cars going around or just under the speed limit jockeying around each other, impeding other traffic from moving around them.

Indeed - this is the 70mph is slower than 50mph thing I mention.

Not sure if we’re talking about the same thing. These slower drivers aren’t any safer: they’re weaving around each other and impeding faster traffic from passing. They’re arguably more dangerous because of that. And the flow of traffic is constrained to the speed they choose, which is on average slower than it otherwise would be.

While they are correlated, flow does not equate to capacity. You can have better flow while still having reduced capacity. That’s not pragmatic.

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