Dear Alice,

I live on a quiet, tree-lined street that seems to attract every taxi driver in Tokyo in need of a break. They pull up along the side of the road, drop their seat back and settle in for a good nap. I wouldn't have a problem with this except for the fact they leave the engine on while they snooze, sometimes for as long as an hour! It drives me crazy to think of the energy they're wasting, not to mention the air and noise pollution they inflict on me and my neighbors. What the heck are they thinking? And why the heck isn't there a law against it?

Rebecca R., Tokyo

Dear Rebecca,

Actually, there is. In Tokyo, and many other parts of Japan, it's illegal to leave your motor running when parked, and the law applies not only to taxis but also to trucks, buses and regular passenger cars. The idea is to protect the environment by reducing carbon-dioxide emissions, but as you pointed out, idling also wastes energy and creates heat and noise — the last thing we urban dwellers need, especially in these hot summer months.

So why do drivers do it? Sometimes for personal comfort, like to keep the air conditioning running, but more often it's because of outdated notions, including that cars need to warm up before being driven; that restarting the car uses up more gas than letting it idle; and that repeatedly restarting your car is hard on the starter and battery. None of these myths is true. Modern engines need only a few seconds of idling before they can be driven safely, and frequent restarting actually does less damage to the engine than leaving it idling, which forces it to operate in an inefficient mode that eventually degrades performance and fuel efficiency.

In terms of gasoline consumption, experts have determined that you'll save on gas by switching off the engine during even very brief stops, leading to the surprising "5-second" rule: If it looks like you'll be idling for more than 5 seconds, turn off the engine and restart when you are ready to roll. In Japan, the recommendation is to do this even at red lights, which are likely to keep you waiting at least 30 seconds, and a lot longer if traffic is bad.

But most drivers consider it too much trouble to restart. To address this, there are now aidoringu stoppu ("idling stop") systems that automatically stop and restart the car without the driver having to turn the key. These work in different ways, but a typical system cuts the engine when the brake is applied as if for a full stop and restarts it when the driver steps on the accelerator. To encourage drivers to adopt these idling-stop systems, the Japanese government offers subsidies that cover half the cost, whether retrofitted (atozuke) or purchased as an option on a new vehicle. The choice of cars is limited and you have to apply in advance for the subsidy (hojokin), so be sure to consult with the dealer well before you want delivery.

The Energy Conservation Center, Japan, in Tokyo, conducted an interesting field test in 2002 to determine how much gas can be saved by cutting back on idling. They took three cars, one with a regular engine and two with different idling-stop systems. They put professional drivers behind the wheel and had them drive most of the length of Japan, from the Soya Peninsula in Hokkaido to the Sata Peninsula in Kyushu, a total of 3,717 km. The cars traveled together so that driving conditions would be identical, and the drivers rotated vehicles and changed the order of the cars in the caravan. When in the normal car, the drivers idled during stops; in the other cars, they utilized the idling-stop feature at their discretion.

As I hope you'd expect having read this far, the idling-stop cars guzzled less gas — 5.8 percent less overall, with a 13.4 percent saving in city driving and a 3.4 percent reduction in rural areas. But what's really fascinating is how much time the cars spent stopped: 24 percent of total driving time, and a whopping 47 percent on urban roads!

"And that's just an average of the cities they traveled through," Yoshirou Shibata, head of the Idling Stop Project Office at ECCJ, told me. "In congested cities like Tokyo and Yokohama, drivers probably spend more than half of their total travel time actually stopped."

So city drivers, in particular, have plenty of opportunity to cut back on idling, and even modest reductions offer benefits. The average car burns 130 cc of fuel in 10 minutes, so if you cut back on idling by just 10 minutes a day, over the course of a year you'll save 47 liters of gas. With gas now hovering at around ¥170 a liter, that's almost ¥8,000 a year back in your pocket. And if that's not enough to motivate you, consider that 10 minutes of idling unnecessarily releases 307 grams of carbon dioxide into the air, at a time when the government is calling on every individual in Japan to reduce their CO2 output by 1 kg a day to fight global warming.

Fortunately, most taxi operators are proactive about reducing idling, with good reason. One company, Rakuyo Kotsu in Kyoto, found that vehicles with idling-stop systems consumed on average 35 fewer liters of LPG fuel per year compared with its regular cars. That saved the company ¥33,600 per car, while reducing its CO2 output by 1,260 kg for every idling-stop car operated for a year. By the end of last year, Rakuyo Kotsu had 116 idling-stop taxis, and will convert the entire fleet by 2011.

But even if taxi companies instruct staff to quit idling, in practice it's up to the individual drivers. So to deal with those idlers outside your door, I'd start with a polite request direct to the driver, such as "Aidoringu o yamete moraemasen ka?" ("Won't you please stop idling?"). If that doesn't work, shift into high gear and call the company, preferably with the date, time and car number.

Puzzled by something you've seen? Send a description, or better yet a photo, to [email protected] or A&E Dept., The Japan Times, 4-5-4 Shibaura, Minato-ku, Tokyo 108-8071.