Local leaders have been extolling the benefits of bicycling. Provo Mayor Lewis Billings led the annual Bike to Work Day in May. The same day, Salt Lake City Mayor Ralph Becker and county Mayor Peter Corroon led a similar trek.

And of course when all these experts agree, we immediately think: What's the catch?

There seems to be little doubt that more people are cycling, just as, in the era of $4 gas, more people are taking the bus or just staying home. The best estimates are that at least 25 million people ride a bike at least occasionally, and anecdotal evidence suggests that number is rising fast.

In fact, the bike craze is going so strong that last week the Los Angeles Times reported what may be a first even for L.A. -- a bike-by shooting. Two men on bicycles wheeled up to a man and a woman, pulled out guns and shot the pair. The victims were hospitalized and last reported to be in stable condition. But when even gang-bangers eschew fancy wheels and settle for a couple of pimped-out Schwinns, you know bikes have arrived.

There's a lot to be said for riding a bike. For one, it's just plain fun to whir down the street on one. Plus, there's the free exercise. Many folks will fork over good money for membership in a gym where they can ride a bike that goes nowhere. People on a real bike get a good workout, without pounding away on their knees as in jogging, and having to fight to use the exercise equipment at a gym -- and without sharing the bathwater of dozens of other people at a swimming pool.

Plus it's fun to watch the scenery go by. You can even do practical errands.

Bicycling gets you outside, where you can soak up the sun and feel the breeze on your face. Speaking of which, Utah presents a fairly hospitable face to bicyclists. In the valleys, the land is generally flat; the mountains provide more thrilling rides.

Yes, it's hot in the summer in midday, but a ride in the morning or early evening can be pleasant. After all, Utah doesn't have the brutal humidity of the Midwest or South, it seldom rains in the summer, and the fall and spring are fairly moderate.

Yet, all is not well. Some motorists complain that cyclists are more reckless than auto drivers, paying little heed to the rules of the road. And Utah drivers sometimes seem to think that anything smaller than a light pickup truck doesn't really count. For safety, even Mayor Billings's bike caravan in May was led and followed by police cars.

So you need to remember that when you're pedaling around Utah Valley without your own escort of armed guards in big sedans with flashing lights on top. It's a time for vigilance and caution.

As for benefits, it might be wondered if there really is any impact on global warming. That's because (and we don't mean to insult anyone) all bicyclists emit larger than normal amounts of greenhouse gases, otherwise known as carbon dioxide.

Speaking of emissions, a seldom-mentioned problem is the question of hygiene, after arriving at work sweating after a refreshing bike ride. A handful of employers offer showers for employees. But most places, you're on your own, and you'll find yourself alone, too, unless you can contrive some way to clean up.

Does biking even save money? If you aren't putting gasoline in your car, you're still putting fuel in your own tank. We read on the Internet -- so it must be true -- that the fuel needed to produce the extra food you'll eat when you bicycle offsets any cuts in your gas use.

So we will testify that whirring down the road on a bike is fun and healthy. But as a bike rider must be alert for every parked car whose driver might suddenly fling open the door into the rider's path, you must also be very, very alert when our leaders urge you to ride your bike. After all, you never really know what they're peddling.