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If 5 out of every 1,000 cars were driverless, traffic problems could be gone for good according to a report by Opel.

If that seems like a small number, consider this -- the cars will gather data on traffic conditions as they drive and turn it over wirelessly as they pass relay points. Traffic managers can use that information to guide decisions on how to control traffic, saving fuel and stress for everyone.

These cars don't even necessarily need to be driverless. As long as a car is wifi-enabled, it can still be controlled by good old-fashioned manpower.

The takeaway is this -- it will only take a small number of wifi-enabled cars to greatly improve everyone's driving experience.

The world-famous Eiffel Tower. There is a secret military bunker that goes below the surface next to the famous tower. CNET took a look.

(Credit: Daniel Terdiman/CNET)

PARIS--If the Eiffel Tower makes you think of a direction, I'm willing to bet it's up. But for some people, the iconic French landmark can also mean down.

Down, as into a "secret" military bunker that has an entrance just feet from the south pillar, or leg, of the tower, and which then goes underground and which is full of Eiffel Tower history and even legend.

Secret of course, is a marketing term when it comes to this bunker, since it is open for a small number of weekly public visits. But because it belonged to the French military, it comes with a heady dose of intrigue. It's said even now that there is a tunnel that stretches from the bunker all the way to the French Ecole Militaire--military academy--at the other end of the famous Champ de Mars park. But, we're told, maybe no one outside the army really knows if that's true.

The Eiffel Tower, behind the scenes (photos)

I've come here on Road Trip 2011 for a behind-the-scenes tour of the Eiffel Tower. And we've started below ground since what better way to grab someone's attention at one of the tallest attractions in Europe than to lose altitude.

Whether there's a lengthy hidden tunnel from there, there's more than one surprise to be found: a passageway with a ghost that echoes shouts on command. The ones yelled in the direction of a small gate that disappears into oblivion, at least.

What there really is here is a collection of wonderful photographs of the tower's earliest days, as well as a pictorial recounting of some of its most important milestones. This is a tower that was built for the World's Fair of 1889--in just two years, two months, five days--and which was originally slated for just a 20-year run dominating Paris' skyline.

But the tower's designer and spiritual guide, Gustave Eiffel, had other ideas. He knew that if he could bestow upon his baby some crucial attributes, it might survive. And so the Eiffel Tower became home to some of the earliest radio transmissions, as well as to the most cutting-edge experiments in meteorology, astronomy, and the monitoring of "physical and air resistance phenomena."

And, as you may have guessed, he saved the tower. Today it is home to a nest of antennae, and over time it has been the source of broadcasts like that of the coronation of Queen Elizabeth II of England in 1953.

Hydraulic elevators
Another side of the Eiffel Tower that isn't usually on people's radar is the engine room that runs its original hydraulic elevators. A relic of the tower's nascent days, these are nevertheless still a fully functional part of the every day operations. And again hidden from the view of the general public, treasures await historical infrastructure geeks: beautiful, archaic systems that are said to be much more efficient than the modern-day electric elevators that share the duty of bringing visitors up from the ground.

The doors to the hydraulic elevators first opened in 1899. According to an official Eiffel Tower accounting, the yellow "chariots,"

"mounted on a carriage and kept horizontal by a leveling system are pulled upwards by cables that move in line with two parallel pistons located underground, via a cable drum system--the cables themselves, the ends of which are attached to the passenger compartment carriage--run back and forth eight times over two sets of pulleys, one of which is fixed and the other attached to the moving pistons, thereby ensuring that the [elevator] passenger compartments can travel [420 feet] , i.e. eight times the piston travel--of 52 feet.

"The pistons are actuated by a water circuit with a pressure of 40 to 60 bar which until 1986 generated motion thanks to three large accumulators of some 200 metric tons each which provided both the pressurized water reserve--the energy to drive the motion--and the counterweight function.

"Since modernization in 1986, high-pressure oil-driven hydraulic motors drive piston carrier motion while two of the three accumulators serve as counterweights."

What this really means is that down here, behind the walls, and at the base of the great elevators that take guests to the 377-foot-high second level, there is some beautiful, very old infrastructure. And though it's the electric elevators that take people up to the 905-foot-high third level--with all the antennae bringing the tower's total height to 1,063 feet--those are the less reliable. The 100-year-old-plus systems are the ones that break down less.

Going up the tower
Going to the top of the Eiffel Tower is something that's not for everyone. If you go as high as you can go, you're exposed to the elements--though protected by a level of fencing that keeps everyone in--and it's a long, long way down.

When I was a kid, I went to the top and had to hug the wall to keep from freaking out completely. These days, I'm a bit better at taking heights, and I actually enjoyed standing at the edge and looking at the tiny people, cars, buses, houses, and so on, far below on the streets of Paris.

But maybe it was just easier because this time around, there's a functioning Champagne bar on the third level. Bottom's up.

cocaine varies greatly between rich countries.

Ovulation is a really useful biological function. Not only does it facilitate pregnancy — though sperm are in no short supply, the ephemeral egg appears just once a month — but new research finds that it also helps a woman select potential partners by enhancing her "gaydar."

All this complex sexual decision-making is going on behind the scenes, according to a study published online this week in the journal Psychological Science that found that straight women at their peak period of fertility are far more accurate than non-ovulaters at sussing out who's gay and who's not just by looking at a man's face.

"We consistently find that people have no idea they are able to do this," says Nicholas Rule, an assistant professor of psychology at the University of Toronto and the study's lead author. "They come out of the experiment completely frustrated and say, This is so hard, no one can do this, and then we look at the data and they're doing amazingly well."

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Rule and colleagues at Tufts University put 40 Tufts undergraduate women — all of whom were heterosexual and ovulating — through three experiments designed to test their hypothesis that women pay more attention to men's sexual orientation when they're extremely fertile.

First, the participants were asked to look at 80 images of men's faces; half the photos — which were similar in terms of expression and attractiveness — belonged to gay men, while the other half featured straight men. A participant's ability to determine the sexual orientation of the men in the photos was closely associated with how close she was to peak ovulation.

"The closer you get to peak ovulation, accuracy goes up, up, up, peaks at ovulation, then starts to go back down again," says Rule. "There is a linear effect."

Then, researchers substituted 100 female faces — half straight, half lesbian — and performed the experiment again. This time, they found no association between fertility and so-called gaydar, an informal term referring to the ability to intuit a person's sexual orientation.

"It's not just that women are more attentive to nonverbal cues around ovulation," says Rule. "It's really something specific about paying attention to men's sexual orientation."

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Finally, researchers went a step further, asking half the female subjects to read a sexy story in order to "induce reproductive thinking" before repeating the previous two experiments with both groups. The women who'd read the tale — a hokey-sounding beach romance about meeting a handsome guy on an island — were even more successful at predicting sexual orientation than the control group, an outcome that Rule says proves that women's brains are evolutionarily primed for mating during ovulation.

This is hardly the first time that ovulation has been shown to alter women's behavior. Previous research has found that women are quicker to identify a man's face than a woman's face near ovulation; subsequent analysis divined that the opposite held true for lesbians: they were faster to pick out a woman's face. Last year, another study in Psychological Science found that ovulating women are half as likely to call their dads. Why? Because incestuous relationships are more likely to produce problematic offspring, women are unconsciously shunning pop at their most fertile time of the month.

Taken as a whole, the entire body of research suggests that when women have the greatest chance of getting pregnant, they are unconsciously making judgments and perceptions that maximize that possibility.

"Around ovulation, the mind is reallocating its resources in ways that are relevant evolutionarily," says Rule. "It shows us that the link between body and mind is greater than we often think."

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