Myth-Busting: Does constantly changing lanes get you there faster?
We’ve all been there, stuck in a line of ‘slow-moving’ traffic while cars in the outside lane are streaking past. So, does constantly changing lanes get you ‘there’ faster?
THIS IS ONE OF the trickiest myths we’ve explored and that because the answer relies on maths and some philosophy. You’d think because the answer is buried in cold-hard maths that it would be quite a simple answer, but it isn’t and that’s because mathematicians, scientists and philosophers are all of differing opinions.
Before we get to the maths and science behind lane changing and whether it really does get you there faster, it’s worth pausing for a moment to consider your own thoughts on the matter. Personally, I’ve done more than my fair share of commuting on major highways that are constantly clogged. And my own observation is that even if you’re breaking the speed limit and constantly swerving through traffic into too-small gaps you won’t get ‘there’ faster. And that’s because at some point there will be a choke point in the traffic and everyone’s progress will be halted…so, after your dangerous run through the traffic, you’ll still only end up a few cars further ahead than you would have had you stuck to the speed limit of the traffic around you. Or, if numerous studies are to be believed you won’t have.
A study by Nick Bostrom, a postdoctoral fellow in philosophy at Oxford University claims a slow lane is generally created by having too many cars crammed into it. Yep, we all agree with that. The flow-on of that is that if you’re in the slow-moving lane then you’ll spend more time in that lane and take longer to get to your destination. Yep, makes sense too. Bostrom’s solution to constantly changing lanes is to increase the diffusion rate and spread cars out evenly in each lane of the highway, but that goes against the road rules where on a two-lane divided road one of the lane’s is for overtaking only and not for spreading out traffic. And the same goes for a three-lane highway, there’s always one lane set aside for overtaking; intended for emergency vehicles to be able to rip down without traffic getting in the way.
So, increasing the diffusion rate is a fine idea but one that’s unlikely to happen because, well, drivers.
And then there’s a driver’s perception. A study by mathematicians Bryan Dawson and Troy Riggs at Union University in Jackson, Tennessee, suggested that a driver sitting on 90km/h and watching a car overtake them at 95km/h would wrongly assume that vehicle was traveling much faster than that, while the driver overtaking would assume the slower driver was going much slower than they were. The slower driver would, they surmised, see the faster driver and likely want to change lanes.
Similarly, Donald Redelmeier, a clinical epidemiologist at the University of Toronto and Robert Tibshirani a statistician at the University of Stanford, via the help of a computer and real-world observation, determined that the lane that appears to be moving more quickly actually ends up with the same average speed as that of the other lanes, even those that appear to be travelling more slowly. And that most people spend more time being overtaken than they do overtaking other cars.
For instance, they observed that while a car may overtake eight or so others and then return to the ‘slow’ lane, that car would then in turn be overtaken by other cars, creating the illusion that they’re going slower, rather than the more accurate observation that the overtaking cars are travelling faster than the speed limit, because of their perception of the speed of the bunched-up traffic. And then there’s the perception, they observed, that people tend to spend less time checking their rear vision mirror and so, when a driver overtakes someone the car behind them disappears, while when they’ve been overtaken the car that’s overtaken them remains “annoyingly” visible.
Redelmeier and Tibshirani also observed that constantly weaving in and out of traffic will increase the chance of a collision. Indeed, a recent study by VicRoads revealed that, on the Monash Freeway, during peak hour there are roughly 2000 lane changes, per hour, every kilometre. And that for every lane change a driver made, the risk of a collision increased six-fold.
So, while weaving through traffic on a race track might help you to get to the head of the pack, there’s no head of the pack when you’re driving on the road. And, based on the research, it’s likely that rather than getting anywhere faster by weaving on the highway, you’re simply fooling yourself via false perception and, at the same time, you’re increasing the risk of a collision.
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5 Comments
Legality is the key.
I often drive on the 100km/hr M1, no exits or on-ramps with a mix of cars – some driving at the limit and some Sunday drivers out mid-week (grrr). On one 4-5km long straight with 3 lanes, there are always the couple of cars which weave their way, changing lanes continually – they end up maybe 5-10 cars in front by the end of that stretch. Some actually lose position.
BUT – they often don’t do it legally.
– They’ll firstly cut into gaps which don’t exist.
– Many then tailgate to manoeuvre to a position where they can slip across to another lane.
– Worst, I’ve seen a couple of AMG/M3/HSV type cars (& bikes!!) – which floor it to cut across lanes, vastly exceeding the speed limit – for maybe only a few seconds, but totally unpredictable from other driver’s perspective. When that happens, from back in the pack, you see a couple of dozen other cars’ brake lights indicating that they’ve disturbed the whole flow of the traffic in doing so.
An interesting article.
Of greater risk to smooth traffic flow are the “robot” drivers who sit below the speed limit in the far right lane even when not overtaking. Not keeping left unless overtaking creates unnecessary blockages to those who wish to proceed at the speed limit and, as a result, are forced into changing lanes as a result of the robotic self absorption.
Indeed. Folk caught in their sad little world of daily commuting after spending all day at a desk, on their way back to a home they can scarcely afford, to watch brain numbing reality tv, before doing it all again. Day after day. Their whole life.
These are the robot drivers you refer to- and though I agree wholeheartedly that drivers should keep left and do the speed limit (ideally +10%..), I can’t help but pity these poor schmucks and the ‘life’ they lead.
Here’s some psychology for you:
I know full well from experience that changing in and out of lanes doesn’t help you by more than a few seconds if at all, and I get a smug sense of satisfaction when I see someone making some dumb manoeuvres to get ahead, then at the next set of lights, they’re only one car ahead…
AND THEN, when I’m feeling the pinch on time, I’ll be naturally scanning the other lanes for opportunities to get to my destination a bit faster! Genius right…
I have, however, observed that the two lanes will typically move in “waves” (speed up, slow down) which are often out of sync. But by the time you realise the other lane is moving faster and have a chance to change, it has passed the peak of the wave and is on the way down, while the other lane is on the way up, so you do end up worse off!
Hi all. Some dang good points below. Changing lanes sometimes saves petrol. For example when a slow truck enters a multilane road. Changing out of the left lane can avoid the need to brake. It’s also a courteous thing to vacate the lane needed by those entering a motorway. It takes observation and courtesy.
Not all drivers are good at observation. They tend to be the ones who migrate straight to the right lane and peg back to 5kmh under the speed limit. It ensures a free road for 200m in front so there’s less need to concentrate. And their lack of concentration becomes apparent when we see them continuing to accelerate into a situation requiring an emergency stop or a red light.
One of the most stressful things is to ride a bike on a motorway with lane changing jockeys. The guys who tend to indicate 0.5 secs after they crash into the next lane. In that situation I’ve positioned myself behind a semi even if it means I have to slow a bit. The upside is that not many lane jockeys want to grab the lane behind a semi. The flip side is the bike rider who cuts into a drivers safety braking zone with a few ciggy papers width to spare … and then starts tapping his brake to get the driver up his clacker to make a new safety buffer.
And then there’s the clowns who drive at 10kmh under the speed limit on single lane road with double lines … but miraculously speed up to 10kmh OVER the speed limit at EVERY overtaking section.