With its settlement on Jan. 23 resolving all criminal and civil charges relating to Boston's $14.79-billion Central Artery/Tunnel project, project consultant Bechtel/Parsons Brinckerhoff closes the book on a 20-year sweet-and-sour deal. B/PB paid $407.1 million for management errors in Interstate 93 slurry-wall construction and I-90 tunnel-plenum construction, as well as inadequate oversight of contractor overpayments and suppliers' non-specification concrete. It is an expensive write-off but the choice was likely pay or pay.

A big firm like Bechtel could have fought the charges in court and possibly could have prevailed, but at what cost? It would have been debarred from state work (and may still be debarred from federal work), and it would have had to face the stigma and business losses from indictments for manslaughter, fraud and false claims. It made the right decision.

For years, Boston suffered from an inadequate road system that included a 50-year-old knifelike viaduct that split the city center like a watermelon. Something had to be done to join the halves, and that was CA/T.

But the megaproject was cursed by controversy from the start. It initially was a back-of-the-envelope-estimated $2.6-billion job to connect I-90 under Boston harbor with Logan International Airport. It then grew in scope and cost to include the I-93 slurry-wall tunnel, new environmental work, a recordsetting cable-stay bridge and the largest soil-mixing operation in North America, along with 20 years of inflation.

When CA/T wrapped up last December, a new 7.5-mile corridor with two large tunnel complexes, four major interchanges and two massive bridges had eased traffic on two intersecting Interstates. It is an engineering marvel that is revitalizing the city.

Had this initially been structured as a normal design-build or program-management deal, there would have been a better outcome. But Massachusetts was not ready. Budget cuts crippled highway staff, and the state desperately needed management expertise. It hired what it considered to be the best talent, B/PB. Over the years, B/PB provided oversight in a parallel structure with the state, but those efforts were merged in the late 1990's, creating considerable confusion.

Political interference also tainted the job. While engineers were busy designing the best, most cost-effective solutions for complex CA/T problems, some state politicians demanded faster production to meet their timetables. A frenetic environment became frantic, and the pace of construction was relentless. Except for the tragic death of Milena Del Valle, CA/T was a project remarkably free of corruption and death. It is a credit to the industry.