Despite the heated level of discussion about the proposed downtown redesign plans, discussions have generated more smoke than fire. On the one hand we have the recurrent drumbeat from City Hall promoting the benefits of the plan, and numerous letters in the Daily Hampshire Gazette pointing out potential problems with it. I write in the hope of focusing this debate in a more constructive way.

As a retired political science professor from UMass where I dabbled in public policy along with international relations and environmental politics, I stressed that studying proposals such as this requires a cost-benefit analysis. Is the proposed policy better than the existing state of affairs, and is the additional cost justifiable?

To date, the vast majority of the views expressed in the Gazette do not weigh the costs and benefits. More to the point, they celebrate or lambaste the virtues of the proposal, without evaluating whether it is better than existing conditions at an acceptable price.

At a price of $21 million and three years of likely diminished income for already beleaguered Main Street, we must seriously consider whether this new project is warranted.

In particular, there are several elements worthy of further analysis.

■Cost sensitivity. How accurate is the estimate of $21 million?

■The safety benefits of a bike lane. How many lives, injuries and bike/automotive repairs will be averted?

■Making Northampton more bike-friendly. In principle this is a great idea from an environmental and health perspective. Yet we really don’t know if bike lanes or reduced parking will sufficiently incentivize people to resort to bicycles, particularly given the age demographics of Northampton, with a median age of 40, and with 44% over age 45. New England may not be the most hospitable area for bicycling anyhow, with extreme winters and summers, and widely variable daytime weather. How does Burlington, Vermont do it?

■The effects on downtown businesses. Given the three-year time frame for the construction, how will businesses survive with fewer customers? Economic theory would predict that at the very least we will see a move toward more chain stores downtown, and more worrying would be the continued death spiral of Main Street commercial occupancies.

■Parking. Switching blocks of Main Street from angled to parallel parking may not be that worrisome in terms of parking spaces, but it will be challenging for people who are not confident parallel parking.

■Total numbers of parking spaces. How much of a difference will the loss of 57 spaces downtown really make? We already face seasonal declines of about 50 spaces for summer al fresco dining. Has City Hall provided any studies of garage usage and whether there are sufficient spaces in the garage and other downtown lots to make up for the loss?

In short, there are a number of potential issues with the redesign plan, and we need to be confident that the real financial and logistical costs justify the pain the plan will cost.

Peter M. Haas is professor emeritus in Department of Political Science at the University of Massachusetts Amherst.