In theory, being concerned about the added traffic (the additional number of car trips) a new development will create is helpful. It recognizes that increasingly, the new form of pollution in our age is not belching smokestacks and sewer pipes so much as it is the number of car trips coming from the new development. But conventionally and historically, our "remedy" has been to widen the nearby roads, add huge seas of asphalt parking, and make the street intersections enormous.
It has been only recently that we are finally starting to realize that this "remedy" ironically makes things worse. Such a "remedy" accelerates urban sprawl, chases away residences (which cannot tolerate proximity to car-intensive areas), makes it more difficult to walk, bicycle or use the bus, degrades our quality of life, moves us closer to being an "Anywhere USA" instead of a unique town, and forces us to make nearly all of our trips by car. (remedies that make cars instead of people happy create the "induced traffic" problem in which we stimulate new, additional car trips that would not have occurred had we not tried to make cars so happy with wider roads and more parking).
Instead, our concern about a new development and the car trips it will potentially generate should be focused on strategies that are effective in reducing this new form of "pollution." We need to insist that the new project, when feasible and appropriate, is walkable, and mixes residences with offices, retail, services, schools, and parks. That is, we need to return to the timeless, traditional, pre-WWII way of building our town and neighborhoods.
It is only through this approach that we can ensure that new developments deliver a quality of life that is free from excessive car trip "pollution" -- developments we can look forward to, instead of dread.