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<blockquote style="position: relative; padding-left: 55px;"><section><a href="https://social.coop/users/shauna/statuses/110193630238218474">Shauna GM (shauna@social.coop)'s status on Saturday, 06-Jan-2024 17:58:40 JST</a><a href="https://social.coop/@shauna" title="shauna@social.coop"><img src="https://gnusocial.jp/avatar/84683-48-20230122200954.webp" width="48" height="48" alt="Shauna GM" style="position: absolute; left: 0; top: 0;">Shauna GM</a><div><a href="https://social.coop/@shauna/110193598297502234" rel="in-reply-to">in reply to</a></div></section><article><p>You might think road engineers would update their guidelines, but apparently they haven't! </p><p>Moving on. How do road engs determine the speed limit for a road? Turns out they measure how fast cars are already going on it Usually about 85% of the cars are going the same speed, and 15% are going faster. They set the limit at that threshold between the average speed and the 'fast car' speed.</p><p>"We look at how fast cars are going and we assume that is the safe speed of the roadway" says Dumbaugh</p></article><footer><a rel="bookmark" href="https://gnusocial.jp/conversation/1385740#notice-5047375">In conversation</a><time datetime="2024-01-06T17:58:40+09:00" title="Saturday, 06-Jan-2024 17:58:40 JST">about 11 months ago</time> <span>from <span><a href="https://social.coop/@shauna/110193630238218474" rel="external" title="Sent from social.coop via ActivityPub">social.coop</a></span></span><a href="https://social.coop/@shauna/110193630238218474">permalink</a><h4>Attachments</h4><ol><li><label><a rel="external" href="https://gnusocial.jp/attachment/2071970">As development arrives on a new road, congestion follows, and the road slows down. Chief among the rules taught to traffic engineers is that congestion is a problem and slow is ineffcient, so postdevelopment, traffic engineers will reevaluate the speed limit. They decide the new speed limits by conducting a study that looks at how fast everyone is driving on the street. Then, they chart those speeds by frequency. Almost always in these studies, the majority of people are found to be driving at a similar pace, but around 15 percent are found to be driving much faster than everyone else. Traffic engineers use this latter group as their limit—setting the speed limit at the low end of how fast the fastest 15 percent drive, which is the high end of how quickly the other 85 percent drive. They call this the 85th percentile speed. It is how engineers set speed limits on major roads nationwide.** “We look at how fast cars are going and we assume that is the safe speed of the roadway,” says Dumbaugh. **“Note that this has no safety basis: it’s simply assumed that most people don’t want to get into a crash and are thus doing what it is safe for them to do.”</a></label><br><a href="https://social-coop-media.ams3.cdn.digitaloceanspaces.com/media_attachments/files/110/193/633/037/113/559/original/aa1132784442b03e.png" rel="external">https://social-coop-media.ams3.cdn.digitaloceanspaces.com/media_attachments/files/110/193/633/037/113/559/original/aa1132784442b03e.png</a></li></ol></footer></blockquote>

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Shauna GM (shauna@social.coop)'s status on Saturday, 06-Jan-2024 17:58:40 JST Shauna GM
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You might think road engineers would update their guidelines, but apparently they haven't!
Moving on. How do road engs determine the speed limit for a road? Turns out they measure how fast cars are already going on it Usually about 85% of the cars are going the same speed, and 15% are going faster. They set the limit at that threshold between the average speed and the 'fast car' speed.
"We look at how fast cars are going and we assume that is the safe speed of the roadway" says Dumbaugh
In conversationabout 11 months ago from social.cooppermalink
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1. As development arrives on a new road, congestion follows, and the road slows down. Chief among the rules taught to traffic engineers is that congestion is a problem and slow is ineffcient, so postdevelopment, traffic engineers will reevaluate the speed limit. They decide the new speed limits by conducting a study that looks at how fast everyone is driving on the street. Then, they chart those speeds by frequency. Almost always in these studies, the majority of people are found to be driving at a similar pace, but around 15 percent are found to be driving much faster than everyone else. Traffic engineers use this latter group as their limit—setting the speed limit at the low end of how fast the fastest 15 percent drive, which is the high end of how quickly the other 85 percent drive. They call this the 85th percentile speed. It is how engineers set speed limits on major roads nationwide.** “We look at how fast cars are going and we assume that is the safe speed of the roadway,” says Dumbaugh. **“Note that this has no safety basis: it’s simply assumed that most people don’t want to get into a crash and are thus doing what it is safe for them to do.”
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