Slashdot Mirror
Math Says You're Driving Wrong and It's Slowing Us All Down (wired.com)
A new study in IEEE Transactions on Intelligent Transportation Systems mathematically suggests that if you and everyone else on the road kept an equal distance between the cars ahead and behind, traffic would move twice as quickly. From a report: Now sure, you're probably not going to convince everyone on the road to do that. Still, the finding could be a simple yet powerful way to optimize semi-autonomous cars long before the fully self-driving car of tomorrow arrives. Traffic is perhaps the world's most infuriating example of what's known as an emergent property. Meaning, lots of individual things forming together to create something more complex. Emergent properties are usually quite astounding. You've probably seen video of starlings forming a murmuration, a great shifting blob of thousands upon thousands of birds. Bats flying en masse out of a cave is another example, swarming sometimes by the millions through a small exit. And scientists are just beginning to understand how they do so.
Common sense says we don't need math to show what is slowing down traffic. Maintaining distance really means matching speed, acceleration, and deceleration. If those happen distance itself becomes less of a key factor. Added distance is just an aid for drivers who aren't good at staying with traffic flow.
If you want traffic improvement,
1) get left lane laggards to drive properly and not slow down faster traffic
2) get everyone to be expeditious when intersection lights turn green
3) teach people not to contribute to traffic compression waves by over decelerating and then under accelerating
Exactly. Overall traffic flow seems most efficient if traffic on main routes is bunched into "packets" of vehicles with gaps between packets large (long) enough to allow traffic from smaller routes to enter or merge onto the main route. My home town did this with updated lights and sensors about thirty years ago (!). Once on the main road you never had to be stuck at a light until all reaching the next town.
The sweet spot is well known - it's around 50-60. That's why insurance companies offer people in that age bracket the lowest rates - they have the fewest accidents.
Keeping constant spacing and running at a reasonable speed within a lane may be good. But holding the same speed in adjacent same-direction lanes is very bad.
In driving classes, back in the mid-20th century, we were warned against it. You NEVER were to hold the same speed as a car in an adjacent lane. (About a 5 MPH drift, with leftward lanes faster, was close to ideal.) Judging by the behavior of current drivers on California freeways that lore has apparently been lost.
Some of the issues:
- Adjacent cars form a multi-lane "rolling roadblock". Drivers behind them who wish to travel faster are impeded, collect behind them, and end up "compressed", setting up the conditions for a chain, reaction multicar pileup.
- With an inter-lane drift a driver wishing to pass a slower car soon has an opening to switch lanes and proceed.
- With the slowest lane to the right and increasing speed to the left, merges and exits require less speed change and have better timing margins, long-distance traffic proceeds rapidly with little disturbance, and lane changes are easy. Drivers have the opportunity to rapidly distribute themselves among the lanes and drive at a speed where they're comfortable.
- When driving at the same speed as an adjacent vehicle you increase your risk of collision:
- If you're in a blind spot you STAY in the blind spot for a long time. The window of opportunity for the adjacent driver to happen to make a lane change into you - or into the space immediately in front of you, becomes much larger than if you had a relative drift.
- If you hold relative position the other driver's peripheral-vision motion detector doesn't keep him aware of your presence. After a minute or so you're likely to fall out of his attention. Then, if a sudden traffic situation makes him need to change lanes suddenly (or he just wants to change lanes and forgets to do a recheck), he may swerve into you.
(By the way: The two-way two-lane equivalent of the rolling road-block chain-reaction-collision precursor is the "rat pack", a term of art in traffic engineering. It occurs when the first driver goes slightly over the limit and the second driver won't pass because he doesn't want to risk the necessary speed, but follows too closely for following cars to pass in two single-car hops. Fault is primarily on the second driver.)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
100 mph is not nearly as dangerous as you make it out to be, especially with modern cars.
I used to race motorcycles and even drag raced both cars and motorcycles, so 100+ mph is no stranger to me. But most people do not have the reflexes to go much over 70. It is pretty simple math distance traveled versus reaction time. At 100 mph, you are travelling around 147 feet per second. That's almost 75 feet in 500 milliseconds.
And there is quite a difference when everyone is going near the same speed and when you are trying to go 100 + on a road where most people are driving at 70. A real pucker string moment when that person you are going 30 MPH faster than pulls out in front of you say 20 feet in front of you.You have less than a half second to react, brake and slow enough to not run into them.
Even way back then, I reserved my faster driving for the proper place. And of someone thinks that driving like that on a roadway where most are diving a lot slower - yeah - they are still idiots.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.