Driving You Crazy: Why do folks follow so closely? If they'd just back off, traffic would flow!

Mind the gap, the secret to high capacity traffic.
Posted at 10:00 AM, Aug 02, 2016
and last updated 2016-08-03 06:08:02-04

Becky from Denver writes, “What is driving you crazy? I-25... Why do folks have to follow so closely? If they'd just back off, traffic would flow, instead of constantly having to brake! Also, why must there always be a slow-down for Sun glare? Buy sunglasses!”

Becky, I used to feel anxious when the driver behind me was riding up my tail pipe. No one that I talked to about this story really likes it but following too closely I found is somewhat subjective. What is comfortable for me isn’t the same for what’s comfortable for my wife. In the Model Traffic Code For Colorado, following too closely reads, “the driver of a motor vehicle shall not follow another vehicle more closely than is reasonable and prudent, having due regard for the speed of such vehicles and the traffic upon and the condition of the highway.” In other words you know it when it is happening to you or when the police sees it.

The Colorado State Patrol tells me if you see someone following too closely or acting aggressively in any way then they want you to give them a call on their *CSP (*277) number. Even if a trooper isn’t in the area or they don’t see the behavior, after three complaints the registered vehicle owner is sent a warning letter that encourages the driver to drive nicer. If additional complaints are called in then a trooper pays that person a personal visit and has the option to take “enforcement action”.

As for your complaint that traffic would flow better if drivers would “just back off” is better addressed by saying the secret to high capacity traffic flow is what I call preserving the gap.

It is best demonstrated by the video attached to this story. Researchers in Japan show how a traffic jam appears for no apparent reason. When all the drivers follow each other at a constant speed with a sufficient gap, traffic flows perfectly. When one driver taps the brakes, or breaks the gap, the driver following has to hit the brakes and so on and so forth and there is your traffic jam that rolls along like a wave through all the drivers on the track. The gap was broken and the effect is the same on the highways. 

In a perfect world, there would be adequate gaps between every vehicle allowing traffic to flow smoothly. The gaps would be large enough to accommodate any minor changes in speed or additional vehicles and everyone would get where they want to go faster. But this is not a perfect world. 

To hammer home the point that it comes down to preserving the gap, about the same amount of traffic will flow when everyone is going 60 mph and following at 6 car lengths, as when you have everyone going 10 mph following at just 1 car length. It will work if the gap is not broken. What breaks down the system is when a driver cuts in or speeds up or stomps on the brakes and “breaks the gap” causing a disturbance to the flow. That disturbance causes that ripple wave effect downstream resulting in a traffic jam.

Derek Harkness, a Civil Engineer who worked in transport management says, “For any given traffic flow rate there are two ideal speeds: a slow speed with close spacing and a fast speed with larger spacing. Traveling with spacing outside of the ideal, either too close or too far apart, will reduce flow away from the maximum.” In other words, preserve the gap.

There is actually a similar phenomenon when driving into the bright sun. At some point drivers feel more comfortable driving slower due to the limited visibility, even with sunglasses. That triggers the switch from the high speed flow as talked about above to the low speed flow. When the glare is gone, speeds pick up to normal levels.

It seems sometimes that achieving the perfect high capacity traffic flow will only work in a controlled environment without human error in autonomous vehicles. Obviously that is not how real life works as humans are well, human. And then when you add in any change in the weather like rain or snow and all the distractions available behind the wheel, preserving the gap remains a constant challenge. It’s like the old saying, if “if’s” and “buts” were candy and nuts the world would be a sweeter place. And if we would all drive with a perfect gap and without distraction then I would be out of a job. 

Denver7 traffic reporter Jayson Luber says he has been covering Denver-metro traffic since Ben-Hur was driving a chariot. (We believe the actual number is about 20 years.) He's obsessed with letting viewers know what's happening on their drive and the best way to avoid the problems that spring up. Follow him on Facebookand Twitter.