It's easy to decide between good and bad, but choosing between good and good is a lot tougher. In the environmental and health arenas, the fields in which I work, such dilemmas are common. They are vexing, and they are fascinating. Emory faces one now.

Over the last several years, a plan for bicycle and walking paths across metropolitan Atlanta has taken shape, spearheaded by the PATH Foundation (www.pathfoundation.org/), pedestrian and bicycle advocates, and others. Recently, Commis-sioner Gale Walldorff, who represents DeKalb County's District 2 (including the Emory campus), has taken a keen interest in the portion of the planned trail that would traverse our part of town. Discussions are under way with University officials, neighbors and others. Some funding already is in place.

The trail, as originally proposed, would run for more than five miles. It would start near North DeKalb Mall and continue west through the South Peachtree Creek Nature Preserve, then through a quiet residential neighborhood, and onward through a forested area along the south fork of Peachtree Creek, crossing under Clairmont Road near the VA Hospital. From there the path would continue along the creek as it passes through Lullwater, past Yerkes, under Houston Mill Road near Hahn Forest, behind the Emory Conference Center, and past Wesley Woods. It would then cross Clifton Road, follow the creek along Old Briarcliff Road, veer west to cross under Briarcliff Road, and continue along the creek toward neighborhoods off Johnson Road.

This is not an innovative idea. Trails along creeks grace many of America's cities--along Rock Creek in Washington, along the Wissahickon in Philadelphia, through Boston's Emerald Necklace, along many of the streams in Minneapolis.

What's good about this idea? The trail would provide a desperately needed transportation alternative in a city that is choking in traffic congestion and the resulting air pollution. In a part of the city with concentrated employment (Emory, the CDC and the VA) and with many residential neighborhoods, bicycle and foot commuting would become safe and feasible. This would offer important health and environmental benefits.

The trail would provide a wonderful setting for recreation, mental restoration and nature contact. Walkers, joggers and cyclists in this part of the city would enjoy a beautiful, forested route. People might exercise more, an important health benefit. They might have a chance to meditate and to commune with nature, enhancing their overall well-being.

The trail also would be an educational asset. Generations of Emory students would be able to stroll under trees and along a stream just minutes from where they live and study. They would learn to appreciate ecosystems and come to believe that urban life and nature can, through forethought and intelligent design, co-exist. They would carry these convictions to other places, and some would act on them, perhaps multiplying the environmental   benefits.

But there's a countervailing good, one that militates against the trail: preserving a precious piece of nature. The forested ecosystem along the proposed trail route is fragile and includes some rare plant species. The trail would run close to a stream, which threatens stream integrity (and indeed is prohibited by the county's riparian buffer ordinance, from which a variance would be needed). The proposed route would run through an educational and research site in Lullwater that the biology department has maintained for more than a decade, and the standard construction design–a 12-foot-wide paved trail, essentially a one-lane road–imposes a large footprint and deposits much impervious surface into riparian zones. In particular, the portion of the trail in Wesley Woods is on a steep slope, where the impact would extend well beyond the trail itself.

Bringing people into the forest might result in littering and other destructive practices. It could encourage invasive plants such as kudzu and privet to spread, choking out the native species that still thrive in some of these locations. Further, human intrusion might threaten the herons, hawks, beaver, foxes and other wildlife that depend on the connected greenspaces that encircle our campus.

This dilemma echoes an old division within the environmental movement between conservationists and preservationists. Conservationists look to achieve a balance between people and nature, and are willing to exploit natural resources if they feel they are doing so in a responsible, sustainable way. Preservationists, in contrast, strive to protect and preserve nature in its wild state, minimizing human intrusions.

A conservationist would entertain the construction of this trail, believing that the benefits could justify the costs. A preservationist would spurn the idea, believing that one of the last remaining stretches of mature forest on campus--indeed, in Atlanta--needs to be protected at all costs. Let people bike on the streets, the preservationist would say. We've paved plenty of surfaces already!

Are compromises available? One would involve modifying the trail design. Instead of a standard 12-foot-wide trail, a 6-foot width would be less intrusive. Instead of asphalt, a "pervious" surface or boardwalk could minimize the environmental impact (sorry, Rollerbladers). Instead of using heavy construction equipment to install the path, the tedious but low-impact option of hand tools, carried in and out by volunteer workers, would be gentler on the ecosystem.

Another compromise would involve altering the trail route to bypass the most sensitive areas. A different, less intrusive route would offer less exposure to natural beauty, but it would better preserve that natural beauty and it would still offer an effective transportation alternative. Emory's campus environmental officer, John Wegner, has been working hard to identify such options.

We likewise need to work hard at this decision, through open discussions across campus. We need to maximize the health benefits of physical activity, nature contact and reduced air pollution, and we need to be steadfast stewards of our natural resources, including streams and forest. We need to be good neighbors and good citizens of Atlanta.

We also need to think on a very long time frame. What sort of a campus, and city, do we want this to be in 50 years? Our ultimate goals must reflect a delicate balance: to promote human well-being and protect the environment today, and to act responsibly and move toward sustainability on behalf of those who will follow us.