9 HN users recommended this explainer9 months2021–2025score 10.5
Years with an HN recommendation, 2007–2026
Recommended again and again in traffic-safety threads as an eye-opener on road design versus posted limits and driver behavior.
Not Just Bikes explains how North American speed limits are set and why posted limits matter far less than street design. It argues that drivers follow the road's cues, so safe speeds have to be built into the street.
“it really opened my eyes on the relationship between rules and actual behavior.” (HN, 2023)
I think my first intro to this was from a Not Just Bikes video on speed limits [1], and that profoundly affected my opinion on this stuff. I now think a lot of road design is just utterly broken, and it includes speed limits, what that channel (and other related) refer to as "stroads", and intersections (roundabouts vs traffic lights). That video in particular is highly relevant to the speed camera thing. [1] [this video]
Profoundly changed commenter's view of speed limits and road design
> MUTCD designs streets similarly to rural highways, and this can create conditions where people speed when they need to be driving slowly, because the design of the street doesn't reflect the speed the sign says you need to be driving. Not Just Bikes covers this shortfall in a video on speed limits[1], and it really opened my eyes on the relationship between rules and actual behavior. Essentially, speed limit signs affect driving speeds slightly, but the street design is important. Wide, open, straight roads naturally prompt drivers to drive to highway speeds, even in more suburb areas. It's amazing how often I check the speedometer and find that I'm driving much more than the posted speed limit when following the flow of traffic. [1] [this video]
Opened commenter's eyes on rules versus actual driving behavior
Europe has a lot more roads with a lower design speed. Curves, narrow lanes, on-street parking, trees/poles/etc close to the road. These things cause people to drive slower, because it doesn't feel safe to go fast. In North America, roads are usually built in the complete opposite way, with long straight roads and wide lanes, so the design speed is actually quite high -- even if that wasn't the intent. People go fast, because it feels safe to go that speed, but isn't, because there are pedestrians and turns. We then "fix" that shit road design by having low speed limits. This video is all I think of when this discussion comes up now: [this video]
Design speed versus posted limits; the commenter's go-to video
Not much but it’s a start. Unfortunately the US treats every street and road like it’s a country road when it comes to speed limits, with a lot of deaths as a result. Great video on this at [this video]
Sorry but this is just so wrong. American road design is super predicated on personal responsibility. We design roads that are as wide as freeways and then put a little sign on the side that says 35mph speed limit. What we need is less focus on personal responsibility and accept that people make mistakes, we're all human after all. Our roads should be designed with human error in mind. The road design itself should make it natural for drivers to slow down near dangerous areas. See this video for example: [this video]
Road design should slow drivers naturally, not rely on signs
It's not about making the roads more narrow or winding per se. It's about deliberately slowing cars down where they need to, through the road design. See this video for example: [this video] Besides that, roads in the US are generally poorly classified. They're often trying to both function as both high throughput roads and destination serving streets. Such hybrid roads are known as "stroads" and they're bad for everyone involved. Stroads are bad for moving cars fast due to the many conflict points (driveways, intersections, etc.) that force drivers to constantly slow down. They are also bad at serving destinations because the many conflict points make stroads very dangerous, especially if you're not in a car. See this video for example: [link]
Not Just Bikes has a great video covering this: [this video] TLDW: People don't obsessively check their speedometer and thus changing the speed limit largely doesn't affect the speed people drive at. To effectively change that you need to change the road design.
Speed limits barely change speeds; road design does
That's not really how speed limits work though. People take their cues from road design and conditions, not what the speed limit actually is. Virtually changing speed limits is dangerous because it causes you to think you are altering the behaviour of traffic without actually doing so. [this video] goes into detail on this
Drivers follow road design cues, not posted limits
Not Just Bikes on YouTube covers road/pedestrian/bike safety extensively. [link] Specific videos: Crossing the street should be safer: [link] How to quickly build a cycling city: [link] Wasting money on car infrastructure: [link] The wrong way to set speed limits: [this video] Safe cycling: [link] "Stroads" are dangerous: [link]
Channel covers road, pedestrian and bike safety extensively
As much as the comments from complaining drivers are frustrating, it reveals that the problem here is relying on speed limits and not street design. If you want drivers to go 20mph, you need to design the street so going any faster feels uncomfortable. [this video] discuses this. Also, I notice that most of those drivers complaining don't address what it's like to have a small child who's a runner and is always trying to get loose of your grip and run in to the street.
Street design, not limits, determines driver speed
The road design is what causes bad or good driving. The road you describe should narrow before the blind curve so the drivers would (often enough unconsciously) slow down before it. For the pedestrian crossing, small islands that separate the lanes and give pedestrians a safe space will help. [this video]
[this video] This feels like doubling down on something that's not super effective. The way to make traffic slower, is to make road lanes narrower. You can also add curves/trees or overhangs to add shadows to the road, which breaks up the roadway and makes it harder to reason about from a distance.
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![Frame from The Wrong Way to Set Speed Limits [ST06]](https://i.ytimg.com/vi/bglWCuCMSWc/hq2.jpg)
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