3 ms·
25+ car lengths between vehicles that the NHTSA recommends Is this hyperbole? I tried to Google for it, but I could not. The best I could find was the three
by throwaway2037 3y ago
25+ car lengths between vehicles that the NHTSA recommends
Is this hyperbole? I tried to Google for it, but I could not. The best I could find was the three second rule. Some back-of-the-envelope calcs: Length of Honda Accord (according to Google): 192 inches. 75 miles per hour / 60 minutes per hour / 60 seconds per minute * 5280 feet per mile * 12 inches per foot * 3 seconds / 192 inches = 20.625 car lengths. Even three seconds isn't enough to reach your recommendation of 25+ car lengths.
Note: 75 mph is 120 kmh
- bombcar 3y agoThe actual calculation involves how fast the vehicle you’re following can decelerate, and your reaction time. You can (usually) follow a large semi a bit closer because its braking distance is longer than yours. But because of reduced visibility you can end up with “revealed brake checkmate” where the semi swerves into the next lane because a vehicle is stopped in the lane, which you then need to swerve or hit.
- deleted 3y ago[deleted]
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- bumby 3y agoThey recommend estimating 4.5 seconds of stopping distance. But that’s very conservative and probably not realistic.
- throw10920 3y agoThat's ridiculous. There's nothing "unrealistic" about 4.5 seconds of stopping distance - how could there be, are you thinking that the highways physically wouldn't fit all the cars spaced at that length?
- bumby 3y agoIt's unrealistic if you expect the existing infrastructure to meet both that requirement, the capacity requirements, and the time requirements of people travelling. In the real-world, there are tradeoffs. People who don't understand that tend to have superficial understandings of the problem because their mental models show little nuance.