SAUGUS – The big question isn’t why the Belden Bly Bridge needs to be replaced – age answers that – but many residents are wondering why it is going to take a total of nearly eight years to complete.According to Mass Highway spokesman Adam Hurtubise, the state will spend five months repairing the current bridge so it can remain open while it builds a temporary bridge. It is expected to take roughly two to three years to complete the temporary bridge. Once the temporary span is operational, the Belden Bly Bridge will be dismantled and rebuilt from scratch, which is expected to take nearly five years.”It’s pretty complex because it’s a draw bridge,” was Hurtubise’s main explanation on the length of time.Hurtubise said the state must build the temporary bridge in order to minimize impact on both vehicle and marine traffic. But many would argue that the detours created by the project have done anything but minimize the impact of traffic.Selectman Michael Kelleher calls the project misguided and ill-conceived.Klark Jessen, director of communications for Mass Highway, begs to disagree. Jessen said the multi-year time line is not unusual for a large scale bridge replacement project because it is in fact three projects linked together to result in one new bridge. And each of those projects, Jessen pointed out, must be designed, advertised and then built.Jessen said the Belden Bly project is not unlike plans to replace Quincy’s Fore River Bridge. He said the large scale Fore River Bridge project is currently in the preliminary design phase, but the start of the project reaches back to 2005 and isn’t scheduled to go out to bid until tentatively in 2011. Only after the bid process would construction take place.”In terms of comparison, each project is unique,” Jessen said. “However, all must go through the same extensive, public review, design, and construction process involving all stakeholders.”He said considering the project is essentially three separate undertakings spread over an eight-year period, during which there are two periods that include design work prior to construction, the project is really not unrealistic, especially when the result is bridge access during the entire design-construction process.