Cars project a “safe following distance” box on the road + blast an alarm at tailgaters

Posted by xiangkunwan@reddit | CrazyIdeas | View on Reddit | 57 comments

This is a follow-up to my previous post about the same thing

Instead of turning on the taillight, if someone is tailgating you, your car should project a bright box (2-3 seconds following distance) onto the road behind you showing the actual safe following distance they’re supposed to keep.

If they keep creeping into the box? The car starts blasting the most obnoxious, unbearable alarm directly backward at them.

The box scale with speed, so at highway speeds it stretches way back and makes it painfully obvious how unsafe tailgating actually is.

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CatchAllGuy@reddit

Or just project car speed on the road. Cops can see it at night and punish the overspeeding ones. No need of cameras.

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beastpilot@reddit

3 seconds at 80 MPH is over a full football field of distance. Projecting that in daylight would require so much light intensity that it would meaningfully impact fuel consumption.

You could just move over.

Got any stats on how "painfully obvious how unsafe tailgating actually is."? Are rear end accidents a primary cause of injuries on highways?

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SlightSurround5449@reddit

Lmao fuck traffic laws because they’re crazy to expect people to follow is my favorite part of this. Followed by the fact that tailgating causes so much unnecessary braking which is what actually fucks up traffic flow, not leaving too much space.

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beastpilot@reddit

There is no two second following law.

Data proves that the densest traffic flows occur below 2 second following distances, at about 2000-2200 cars per lane hour (1.7 seconds between cars, which is less than a 1.7 second following distance)

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SlightSurround5449@reddit

And how do you interpret “reasonable and prudent”?

How exactly does “densest traffic flow” relate to safety? Because at that distance even half a second of braking in the front creates a pretty large traffic shockwave. Took me literally two seconds to find data that says at least 2 seconds is not only safer but more efficient, and nothing to corroborate “1.7 seconds” tbh.

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beastpilot@reddit

The safest road is one with no cars on it. Any search with 2,400 or 2,200 vehicles per lane hour will show you tons of links to where this is considered the optimal. Which is 1.6 seconds.

https://www.kittelson.com/ideas/how-connected-automated-vehicles-may-change-freeway-capacities/

And these are real volumes: https://www.ctps.org/data/html/studies/highway/Bottlenecks/Express_Highway_Bottlenecks.html

During peak periods, between 2,300 and 2,900 vehicles per hour exit I-95 southbound to I-90 and Route 30. Farther downstream, between 2,000 and 2,400 vehicles per hour enter I-95 southbound from the same roads.

Are you saying that if everyone increased their follow distance, this would become more efficient? Are you aware that physics makes this impossible?

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thegamerdoggo@reddit

Sweetie what big city are you in where the cars are going 75?

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RepairBudget@reddit

There are plenty of places in Houston where if I'm driving 75 I'm being passed constantly.

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thegamerdoggo@reddit

To be clear we’re talking about in the city right?

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RepairBudget@reddit

Yes, but obviously not through downtown in rush hour. Houston has about 120 miles of interstate highways, and over 1200 total miles of highways and tollways.

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thegamerdoggo@reddit

Yeah I mean obviously on the interstates and some highways it’s gonna be really high, I meant like in the city part of houston, in the city city

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RepairBudget@reddit

Depends on the time of day. But yeah, the interstates go right through and around the city city.

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thegamerdoggo@reddit

But not in the city city, it’s its own thing you have to get onto, your not driving in the city your on the interstate going through the city

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RepairBudget@reddit

I think you're trying to say surface roads. And I think you're the only person who thinks that highways in the middle of a city are not part of the city.

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thegamerdoggo@reddit

That’s why I said city city because I was trying to explain to you in simple terms, also I think you Texans are some of the only people who hear the word in the big city and start thinking about the interstate because that’s wild, you should’ve known damn well nobody was talking about the interstate honey

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RepairBudget@reddit

Ok. Only the roads you're thinking of are part of the city. The big roads running through downtown are not in the city. Sure, sweetie. Everybody knows that. 🤣

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thegamerdoggo@reddit

Are the big roads running through your downtown going 70 miles per hour?

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RepairBudget@reddit

Depends on the time of day, but yes.

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thegamerdoggo@reddit

You have time based speed limits?

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RepairBudget@reddit

No, but the actual speed of the traffic varies from about 5 to 85. The posted limits are 60 or 65.

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thegamerdoggo@reddit

Ok well sweetie you should clearly be able to understand the fact that that doesn’t matter, the speed limit is 60, people choosing to go 85 in a 60 doesn’t matter

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RepairBudget@reddit

Let me quote your original question in this thread: "Sweetie what big city are you in where the cars are going 75?". This has been answered clearly and repeatedly, but you're still arguing the point. Bless your heart.

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SlightSurround5449@reddit

Holy shit this thread was a joy. And the condescension from the other side despite being deeply weird? Chef’s kiss.

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RepairBudget@reddit

Agreed. This was the most fun I've had on Reddit in a long time. 🤣

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thegamerdoggo@reddit

Oh you mean when you swapped from not downtown to downtown roads count too, clearly neither of us can keep it straight when explaining things but at least speed limits are consistent and what you obviously should’ve been using darling, just because I go 120 doesn’t mean I’m supposed to

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FriendlyArachnid6000@reddit

Lol just because you can't use it doesn't make it not in the city rofl what do you think all those ramps are genius

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thegamerdoggo@reddit

Oh sweetie thats silly, do you notice how you dont just take a left turn somewhere and now your getting bagels at Einstein when your on the interstate, you have to GET OFF the interstate first, because its a completely separate areas thats handled differently

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FriendlyArachnid6000@reddit

Sweetie, you don't have to be a condescending idiot. Highways through Los of cities reach 70+mph!

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thegamerdoggo@reddit

Not inside where the people are, in the dead parts yeah, also you should learn to read a little better because I did say some highways

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FriendlyArachnid6000@reddit

You're wrong. I regularly drive through the city on the interstate and kids flowing just fine. You were condescending to that other person. Shame on you lol

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thegamerdoggo@reddit

Through honey, through, I can go through a tunnel doesn’t mean in the mountain, your going through the city on the interstate

And I’m still gonna be condescending since yall seem to not be able to tell simple concepts, like being inside a city versus driving through the city

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beastpilot@reddit

Plenty of roads in TX in cities are 75 MPH speed limits.

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xiangkunwan@reddit (OP)

The 85 mph is on a toll road in Texas, (let it be the toll road operator's problem to deal with tailgaters, or pay a price for the system to work at their higher speed) the highest speed limit excluding toll roads is 80 mph in the USA

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Worldly_Owl953@reddit

In the US alone about 26.3 billion per year is directly attributed to rear-end collisions (medical costs, property damage, lost productivity).

Some broader estimates (including indirect costs, congestion, long-term injuries, etc.) push rear-end crash impacts much higher—up to ~$242 billion annually.

Specifically for tailgating (following too close): Around 30–56% of rear-end crashes involve tailgating

Total economic impact tied to tailgating-related crashes is estimated at roughly $50 billion+ per year in the U.S.

On a global scale rear-end collisions worldwide contribute to roughly $500 billion annually in economic losses

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TomPastey@reddit

Hand held laser pointers easily cover the distance with enough brightness to be seen in daylight. We're looking at hundredths of a hp of power consumption.

The much tricker thing is that the projection has to adapt for the curvature of the road. When cresting a hill, the projection is going to hit the driver behind you in the face. When going around corners the projection is going to go off into other lanes or the side of the road. The tracking method for the terrain undulation is going to be complicated.

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Zenith-Astralis@reddit

Hmm. Already putting lasers on the cars? Give then lidar?

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xiangkunwan@reddit (OP)

1 second is for reaction time another second for speed differential (assume 10ft/s^2 deceleration). So a minimum of 2 seconds following distance is required for safe driving (13.3 car lengths at 75 mph, 12.3 at 70 mph, 11.5 at 65 mph, 10.6 at 60 mph)

Phantom traffic jam is caused by tailgaters following too close and braking harder than if they have the correct following distance

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Mundane-Caregiver169@reddit

Thank you, I recoiled at the suggestion that tailgating does anything other than CAUSE traffic issues.

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xylarr@reddit

There's a make of Chinese car here in Australia that flashes it's brake lights quickly (like some cars do when emergency braking) if you follow too closely. It might be the hazard lights, but regardless, the car in front automatically let's the car behind that you're too close.

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WhenTheDevilCome@reddit

I think I just want a system that lowers the front of the vehicle and raises the rear -- on demand -- so that the vehicle assumes the stance of sudden emergency braking, even though I'm not actually stopping. For legal reasons, I don't think the brake lights should actually activate.

The no-brake-brake-check.

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Blueshift7777@reddit

I’m all in favor of shaming people into driving more courteously.

Can we also make it so that green lights blare an alarm when it takes longer than 3 seconds to react to them?

And also alarms that sound when someone turns without a signal? Or when someone is traveling significantly below the speed limit and not getting tf over to let the 20 cars behind them pass since they’re not concerned with getting to their destination in the current century?

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koyaani@reddit

No, because there are many reasons why someone may not immediately proceed at a green light that aren't due to inattentiveness

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Familiar-Lab2276@reddit

So it should be manually operated by a guy with a paintball gun, only the paintball are filled with water.

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Blueshift7777@reddit

If it takes longer than 3 seconds to assess the safety of proceeding through an intersection you aren’t able to think fast enough to drive.

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koyaani@reddit

So I should run over a pedestrian after 3 seconds because why?

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Blueshift7777@reddit

Why is Reddit so needlessly pedantic? You know exactly what situation I’m referring to. Clear intersection. Light turns green. Hit tf gas pedal. That is all.

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Excellent-Stretch-81@reddit

Well, the system will need to be sophisticated enough to make the distinction. It's also going to have to recognize situations where the intersection is clear, but the road beyond is obstructed, since a person should not be entering an intersection if they can't exit it before the light turns red. It will also need to recognize vehicle size, because the space needed for a car to safely clear in intersection is different than the space needed for a tractor trailer. And then that noise pollution is going to affect a lot of other people, like nearby pedestrians and the drivers behind the slow mover who have no control over the situation, or people in their homes trying to sleep when this happens at night.

Implementing a very sophisticated, expensive, irritatingly noisy system when an inconvenienced driver can simply tap on their horn seems like a terrible solution.

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