Since I grew up tweaking cars, watching Formula One, and reading Jack Kerouac, it’s not surprising that I am predisposed to the fast lane. But in the interests of science, I recently decided to spend an entire day driving below the posted limit.
It was the scariest six hours of my life.
The experiment began in Chattanooga, Tenn. My wife and I were headed back to Toronto in a diesel-powered VW Golf, and I wanted to test its peak fuel efficiency, which meant running below the posted speed limit of 70 mph (112 km/h).
I decided to discipline myself to the 90-100 km/h range, a speed that would improve our fuel economy by cutting down on aerodynamic drag (which increases as the square of velocity). The drive would take longer, but we thought it would be a nice change of pace. We’d glide up I-75 listening to classical music as our VW sipped diesel fuel like a hummingbird. My inspiration would not be Andretti, but Gandhi. A beautiful day was ahead of us.
Wrong. Instead, we would get an education on the risks of gross speed differential and mankind’s elastic perception of highway law. We would also get an up-close look at some of the highway’s strangest denizens – as we were about to see, not all bad drivers are fast ones.
This is the story of our day in the slow lane.
Driving below the speed limit on an interstate highway is not a recommended activity. Driving at 90 to 100 km/h on a busy weekend, our VW was like a mobile speed bump. Although a few cars went by slowly enough that we could see the drivers cursing us, most blasted past in streaks of noise and colour, like meteorites rocketing their way into a distant galaxy. Even the trucks were faster than us – they raged past, leaving our little red Golf rocking in their diesel-tinged wakes. Now I knew how Amish farmers must feel in their horse-drawn buggies.
It was going to be a long day. I comforted myself by flicking on the Golf’s trip computer, which showed our second-by-second fuel consumption. On our way south, running above the limit along with the rest of the traffic, we’d burned about seven or eight litres of diesel every 100 kilometres. Now the computer was showing much better numbers – we were averaging around 5.5 litres, and the gauge often dipped down into the two and three litre range.
I loved the economy numbers. But I hated what I was seeing in my mirrors – traffic roared up behind in an endless stream, swerving around us at the last minute. Everyone was going faster than us. Way faster. I realized that almost no one drives at the speed limit, including police. (By the time our experiment ended, we’d been passed by troopers from Tennessee, Kentucky and Ohio, plus half a dozen local sheriffs).
We were getting a first-hand look at a unique phenomenon – our elastic relationship with speed limits. For most drivers, a speed limit is not so much a rule as a loose guideline. According to Jeff Muttart, a former police officer who now specializes in the study of traffic safety and driving behaviour at the University of Massachusetts, the majority of drivers routinely exceed the posted limit on major highway.
“It’s human nature,” he says.
As experts like Muttart have learned, drivers determine how fast they should drive based on a series of factors. A posted speed limit is one of them, but it is not typically the most important. Instead, most drivers automatically base their speed on their ability to process information – the average driver likes at least two to three seconds to contemplate what’s ahead. Another major factor is the speed of traffic – the majority of drivers automatically keep pace with those around them.
How fast people drive also depends on the road, according to Muttart. Given a multiple-lane divided highway like I-75, many drivers will feel comfortable at speeds considerably higher than the posted limit. “We match our speed to what we’re presented with,” Muttart says. “If there’s a paved shoulder, for example, people will drive faster. Take it away, and they slow down.”
We were seeing this first hand. Interstate 75 is a road that promotes relatively high speeds. There are clear sight lines, paved shoulders, and few uncontrolled crossings. The posted limit was 70 mph, but the majority of drivers exceed that – most go just a little faster, but some exceed the limit by a considerable margin.
As we cruised in the 90 to 100 km/h range, most traffic was passing us with a speed margin of 25 to 40 km/h. And at least once every 10 minutes, someone zoomed past doing at least 50 or 60 km/h more than us. (We later saw two of these cars pulled over by police).
Although risks rise with speed, posting an artificially-low limit can create even greater dangers due to a phenomenon known as speed differential (the difference between the fastest and slowest cars). Since some drivers drive at the “natural” speed of the road, while others scrupulously obey the law, a limit that’s too low will increase closing speeds.
I was learning that the hard way. Again and again, cars blasted up behind us, then slammed on the brakes or veered into the next lane. A guy in a rusted Toyota pickup actually passed us on the right, jerking the wheel and cutting onto the paved shoulder in a scary-looking move.
After a few hours in the slow lane, I realized that it was home to a small, peculiar subset of self-selected drivers. A few seemed to be like myself – economy-obsessed hyper-milers trying to eke as much as distance as possible out of every litre of fuel. Then there were the ones who used the lane as a refuge. We passed a slow-moving minivan piloted by a woman who was eating fried chicken from a plastic tray that rested on the top of the steering wheel. Then came a slow-moving Pontiac Sunfire that was oscillating between the slow lane and the shoulder. The rear bumper was held on with duct tape, and the driver looked like a veteran meth-tweaker. A chromed plastic skull hung from his rear-view mirror, and he was holding a spirited argument with a woman in the back seat – each time he turned to yell at her, the Sunfire shifted lanes.
Then came an old, overloaded Ford truck that was doing about 45 mph. The pickup bed was stacked with a teetering pile of engine blocks and steel beams, and the front tires were barely touching the pavement. The driver sawed desperately at the wheel, struggling to keep his unstable machine between the lines. I decided to speed up for a minute, wasting a little gas to leave the pickup well behind.
On most drives, my wife and I flow with the traffic, matching our speed to the majority of the other cars. Now, driving 10 mph below the speed limit, we found ourselves in a new world – and not a good one. In theory, slower is safer. Lower speeds reduce your stopping distance, give you more time to react, and reduce the force of a crash (like aerodynamic drag, kinetic energy increases as the square of velocity, so increasing your speed by a factor of four makes a crash 16 times more violent).
But theory doesn’t take human nature into account, and after six hours, we’d had enough of the slow lane. We felt like the pilots of a lumbering bomber that was being harassed by fighter jets. We’d been passed by hundreds of freight trucks, five motor homes and at least a dozen police cars. And we got the finger twice.
We’d travelled 570 kilometres – about 100 less than we would have at our typical cruising speed. Slowing down did save a lot of gas. I filled up the Golf and ran the calculations – we’d achieved 5.5 litres/100 km. That was an improvement of more than 30 per cent over the trip from Toronto to Georgia, where we cruised at the speed of traffic.
Now we were getting back up to speed (the limit, at least). The slow lane wasn’t a nice place to visit. And I don’t want to live there.
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