I wrote this for the Alexandria Orb web site in 2000
Of course these figures were for adapting the Alexandria Orb in 2001-2001, and not 2007 -?
The Alexandria Orb proposal has precedent in the tale of the Scheme Z portion of Boston's current Central Artery Tunnel Project: the substitution of a newer design for the approach ramps to the new Charles River I-93 and Starrow Drive Bridges, replacing the aesthetically unpopular scheme z (so named for being as the 26th design proposal formally considered, complete with 3D models of each of these 26 design proposals that were placed on public display during the selection process.
Adapting the Alexandria Orb proposal would afford little if any delay, if we take advantage of time between start of bridge construction and the start of construction upon the approaches. Unlike the Scheme Z saga, where there was no citizen's alternative design at its onset, the Orb design already exists and is ready for being refined and adapted to the official project plans.
The Alexandria Orb would likely add a minimum of $100 million to the $609 million FHWA Route 1 interchange design for this $2-2.5 billion project, respectively a cost increase of about 15% or 5% taken for the interchange or the whole project.
Approximately $50 million could be pared from the Alexandria Orb proposal if this design were constructed without the full deck within the Orb roadways (which could still be added at a latter date).The added costs would be a fraction of those for a full tunnel crossing beneath the river.