In a new development in the debate over the Sullivan Square Rutherford Avenue reconstruction project, the city unveiled a new option to build an underpass at Austin Street despite the fact that traffic volumes have taken a nose dive there and would likely decline even more after a series of stoplights are installed on the street. During a presentation on the new “hybrid” option Wednesday night, the Boston Transportation Department also admitted that this would cost more to build and maintain—and would be overbuilt based on the traffic flow through the area. This strange turn of events is widely seen to be a reaction to political pressure from an organized group of Charlestown residents who have brought to their side Congressman Michael Capuano and his liaison in the neighborhood, Danny Ryan.

For the most part, the bike/ped path alongside Rutherford Street is preserved in the proposed hybrid, but the linear park surrounding the path would be reduced in width by around 15 feet, losing close to a third of an acre of open space over the span of the underpass. Even though the bike path is preserved, some cyclists and other residents in the neighborhood spoke out against the underpass, citing noise, high traffic speeds and the fact that a highway like underpass would continue to deter economic development on what are now several large parking lots nearby.

The city made it clear they would build either the underpass or the surface option depending on what the neighborhood desires, but the most revealing part of the Boston Transportation Department’s presentation on Wednesday night was the vast difference between inbound and outbound traffic on Rutherford. Traffic has dropped by as much as 33% overall on the road since 1997, Michael Hall of the consulting firm Tetra Tech told an audience of over 100 at the new Knights of Columbus hall, but traffic counts also indicated that inbound traffic flow was three times as heavy as outbound traffic. Hall explained that this was likely due to the one-way toll scheme on the nearby Tobin Bridge.

In other words, he said, when suburbanites north of Boston roll into town, a large number avoid paying $3 for the Tobin during rush hour by taking Rutherford, but on the way back home, the Tobin is free, and they prefer it.

This is significant because when the new design for Rutherford is implemented several stoplights will be installed, slowing traffic from the 50 to 60 miles per hour speeds of today to roughly 30 miles per hour. Literally dozens of projects from around the country have shown that when a city decides to slow down traffic, the traffic disappears—because a certain percentage of commuters find faster ways to get where they’re going. The price of the Tobin is going to seem a little more reasonable to people who are trying to get to work on time or shave off several minutes of their daily commute.

Hall stopped short of explaining this well known phenomenon among traffic engineers on Wednesday, but he did say that even if all 1,000 drivers decide to keep avoiding the $3 dollar a day fee and traffic levels remain the same, the underpass would still have an extra lane in each direction that isn’t needed to carry the traffic demand.

“It wouldn’t be safe at just one lane,” he said, referring to the need for a breakdown lane and access for emergency vehicles. The proposed underpass would have two lanes in either direction, though the traffic passing through would technically only require one, and could also be handled by the surface option, which was overwhelmingly approved by a group of community residents in 2010.

Charlestown is now divided on the issue. A large contingent commenting toward the “save the underpass” side sounded off on fears of traffic “backing up” and overrunning other streets in the neighborhood, and a smaller phalanx of residents united under the banner of the “Rutherford Corridor Improvement Coalition” cited the need for slower traffic for safety and noise improvements. Interestingly, the goal of groups on both sides of the issue is getting rid of traffic. The real difference lies in their beliefs in how traffic behaves. According to BTD Commissioner Thomas Tinlin, who was also present at the meeting, his agency will not move forward until some semblance of “consensus” is reached in the neighborhood.

To help inform the debate, the Union is hosting two nationally recognized experts on traffic calming and freeway removal at the MGH Charlestown Healthcare Center on 73 High Street this Tuesday night, May 15 at 6pm. Peter Park has served as planning director in Denver, Colo. and Milwaukee, Wis., and Ian Lockwood is a principal at AECOM, a Fortune 500 engineering firm. Both have had direct experience with projects similar to the Sullivan/Rutherford redesign. Their presentation will be followed by Q and A session.