Will Keogh's mornings and evenings are often an exercise in multitasking. Exercise is the operative word here.Barring a torrential downpour, the 33-year-old South Nyack man bikes 16 miles daily from his Piermont Avenue home to his job as a research engineer at Lamont-Doherty Earth Observatory of Columbia University in Palisades.“I enjoy cycling," said Keogh, in his Australian accent. "It keeps me fit. I feel like I never have time to go to the gym.”Keogh was just one of many bicycle enthusiasts who took to the streets and crossed bridges last week in honor of Bike-to-Work Week, which occurs annually during the month of May — or, as it has been known in certain cycling circles for 49 years, National Bike Month.That's not why Keogh hops on his $1,000 Avanti mountain bike, which is equipped with road tires, every morning a little after 8 a.m.“I have more time to think when I'm cycling," he said. "Not having to concentrate on traffic. I have time to think about whatever's happening in my life. Nothing profound. Mostly what I'm going to cook for dinner that night."With rising gas prices and as more people become more health- and environment-conscious, the bicycle once again is being used as a viable method of commuting and not just for recreational use, said Dani Simons, an events and membership director with Transportation Alternatives.The 5,000-member Manhattan-based nonprofit citizens group works to achieve greater ease for bicycling, walking and public transit, fewer cars on the roads and quality-of-life improvements through safer, calmer neighborhoods and car-free parks.Simons said New York City in the last decade had become more bike-friendly, with the addition of bike paths on bridges for commuters. In that time, the number of bicycle commuters has risen from 75,000 to 113,000.The time she spends on her bike on her way to work gives Simons a chance to clear her head, wake up and, like Keogh, get fit.“One in nine people living in the city have a commute time to work of over 90 minutes,” she said. "All that time sitting could be used to exercise, to unwind. My commute is not a burden anymore. It's part of my commitment to a healthier lifestyle."While cycling to work may seem more viable in an urban setting, Rockland — its Hudson River villages in particular — is invaded weekly by cyclists drawn to the greenery, water and restaurants.“This is sort of the biking capital,” said Glenn Davgin, owner of Piermont Bicycle Connection. “It's sort of the destination place. It's definitely the spot to ride.”Davgin said he had noticed an increase in customers who had ditched their four wheels for two.“I could only guess why,” the Orangeburg man said. “Maybe just to be healthy. You're forced to ride home. A lot of guys do it for the exercise.”Rockland's proximity to the George Washington Bridge is a plus for commuters looking to get to jobs in the city, he said.“It takes 45 minutes to get to the bridge. That's just the right distance,” said Davgin, who along with three of his employees often commute by bike to work. “The wind in your face is great. I can't stand sitting in traffic. I bet some days it's even quicker.”Keogh, who has been biking since primary school and was lucky to always live within bicycling distance from his job, said he wished more people would cycle to work so “other motorists would share the road more happily.”His 45-minute route takes him through Piermont, into Tallman State Park, then onto back roads before finally arriving at Lamont-Doherty. He said he avoided Route 9W for fear of drivers.Keogh's wife, Erica Hendy, often joins her husband by biking to work, but more often drives the couple's Subaru Outback.Biking to work in the winter is one thing, but in the warmer months, Keogh brings a change of clothing so he can shower when he gets to work.“I feel,” he said, “completely complacent.”That, he said, is a feeling he rarely gets confined in his car heading down Route 59 on a warm, sunny day.