The trek up Science Hill is about to get even longer.

The Prospect Street Bridge will be closed for about a year starting this summer for repairs, severing the main access route to Science Hill from central campus. The $3.5 million project, which rounds out a trio of embattled bridge replacements, will take place in anticipation of increased future traffic as new construction shifts the campus’s core northward.

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The 89-year-old bridge, at the intersection of Prospect, Canal and Trumbull streets, spans the Farmington Canal, once an industrial artery and now a bike trail. Typically bridges from the early 1900s were only built to last 50 years, New Haven city engineer Larry Smith said, so the repair is long overdue.

Since a 2007 assessment determined that the bridge needed to be fixed, the entire bridge will be replaced, with construction starting between July and August. The intersection will also be redesigned to correct the alignment of the turn at Trumbull and Canal streets.

The bridge is slated to reopen in mid-2010, timed to coincide with the opening of the new University Health Services building on Lock Street. YUHS’s new location is expected to bring more foot and motor traffic to the area, Smith said. So, too, will the two new residential colleges slated to occupy the site whose southernmost corner is the Prospect Street bridge, although their construction has been delayed because of the recession.

YUHS’s current location has been infamously obstructed by the three Farmington Canal bridges; its entrance was long obscured by a maze of fences and barricades while the Hillhouse Avenue Bridge was under construction in 2008. The new Hillhouse roadway cost $2 million and the new pedestrian bridges cost $2.5 million, of which 80 percent was provided by a federal grant and 20 percent by Yale.

The Hillhouse Bridge was supposed to be completed by last summer, in time for the fall 2008 closure of the Temple Street Bridge on the next block. But construction on Hillhouse ran behind and did not finish until the late winter. That meant that for about two months, YUHS was cordoned off on both sides and difficult to reach by car.

In part because of this experience, the replacement of the Farmington Canal bridges has become something of a running joke. Though the bridges span little more than a dry trench, their replacement has been fraught with delay and frustrations, as the engineers discovered after construction had begun that the materials behind the retaining walls were not as strong as expected. The News’ inquiry about the bridges to the city engineer’s office was met with, “Oh no, not the bridge again. Why do we even have bridges?”

Smith said the city “learned our lesson” from the first two bridges, adding that hopefully the third time will be the proverbial charm.

“Fool me once, shame on you,” he said. “Fool me twice, shame on me.”

The replacement of the Temple Street Bridge, which is supposed to reopen later this spring, cost $1 million, two-thirds of which was covered by Yale and the other third by the federal government. The Temple Street Bridge will have to reopen before the Prospect Street Bridge can be closed, Smith said, or else the northern wing of the city would be virtually inaccessible.

As it is, the closure of the Prospect Street Bridge will inconvenience those trying to access Science Hill, both on foot and by car. Donald Relihan, the director of support services who oversees Yale transit, said he will have to reroute at least three of the six shuttle lines to accommodate the road closure. The blue, green and red lines and the Science Hill express will all be affected.

“When you come back in September, you’ll see [the change],” Relihan said.

Relihan said he does not know how the shuttles will be rerouted and is currently trying to figure out how to revise the routes to minimize delays.

The replacement of all three bridges was part of a $10 million development agreement signed in October 2006 between the city and the University.