Less than 20 miles from Baltimore lies Chestertown, Maryland, an almost comically perfect American small town. It has a grassy square, with memorials to its Civil War dead, a main street that is lined with wood-frame houses and shops, and Washington College, founded in 1782. Outside of town are just a few subdivisions formed around the roads there, and then you get into mile after mile of farmland, filled with soybeans and other crops.

How could such a bucolic landscape exist just a few miles from a big city? Because between Chestertown and Baltimore lies a very big body of water, the Chesapeake Bay, which has defined a huge body of land, the Delmarva peninsula. Right now only two bridges link Delmarva to the mainland--the 4-mile Chesapeake Bay Bridge at Annapolis, Maryland, and the 18-mile Chesapeake Bay Bridge Tunnel at Norfolk, Virginia. Both are engineering marvels but provide relatively little capacity in terms of moving people and goods--which is what keeps Chestertown so picture-perfect.

There is talk in Maryland of building a third bridge. Governor Robert L. Ehrlich Jr., who is known as a fan of new highways, put a new bridge on his list of "101 Outstanding Ideas" for the state and a task force has been formed to study the idea.

One of the prime routes for a new bridge would be Chestertown to Baltimore. It's fair to say that if a conventional bridge were in Chestertown, the town and its surroundings would change beyond all recognition. New homes and businesses that would spring up around the roads leading to the bridge would crowd out farming, which is now a vital business.

My question to the state of Maryland is not whether the bridge proposal is good or bad but whether these kinds of scenarios have been sufficiently considered. It's true that planning is just beginning, but when I look over the official "needs" report at www.mdta.state.md.us, the principal justification for a billion-dollar new bridge is that traffic is backed up at the Annapolis-based bridge. I don't read that there is a need for more houses on the other side of the bay, even though that would certainly happen if a new bridge were built.

Whether it's widening an old road or upgrading an intersection, transportation changes the way an area develops and functions. This is--or can be--a good thing. Transportation has a transformative power that cities and states can use to rebuild their economies and make their neighborhoods and cities more functional and pleasing. But this transformative power should be considered before a project is built-- not after. Too often transportation planners, including those in the mass transit world, abdicate their responsibility by simply saying they are "responding to rising demand." Rising vehicular traffic is described as an organic phenomenon, similar to spawning fish, not something that is both caused and limited by the construction of roads themselves.

Trent Kittleman, executive director of the Maryland Transportation Authority, was nuanced in her discussion of the proposed bridge when I spoke with her. She said new ideas were being considered, such as building the bridge through Kent County but without off-ramps there, so bridge-generated growth "would not destroy the communities around it." Another idea would be to build a new bridge much further south, through the Blackwater National Wildlife Refuge, precisely because growth would be impossible there. While this is an interesting idea, in my mind it raises the question that if growth is not desired, why build a new bridge at all?

An idea that occurs to me is to build a bridge that would accommodate a train line as well as vehicles. A train line would actually have many times the capacity of new lanes of highway and so would whisk people back and forth while their neighbors were stuck in line waiting to get over the bridge in their cars. Growth around station stops could be accommodated in more compact form.

Kittleman was not so thrilled at the idea of a train line. "There is a good deal of capacity with a train, but there are not a lot of people who want to use transit," she says before adding, "We're just not set up for transit."

That's not quite logical. It's like saying people don't want to drive and then failing to notice there aren't any cars or roads around. Her apparent confusion may stem from the inherent paradox that is transportation: That is, it is simultaneously about moving things between places and making new places as well.