The long-awaited fourth bore of the Caldecott Tunnel, which became a welcome addition to our transportation network Saturday, deserves to be recognized for the grand accomplishment that it is.

Burrowing 3,400 feet through the base of a mountain and hauling away 6.4 million cubic feet of rock and soil is an impressive task in any era, but with the environmental and safety restrictions of the 21st century it was like running a marathon with leg irons on.

A $3.5 million sound wall on the Oakland side was required for noise abatement. The site had to be regularly sprayed to curtail construction dust. Endangered species could not be harmed, uprooted trees had to be replaced and seismic considerations were ever-present. Geologic samples were tested for hydrocarbons, readings were required for gas leaks, and no hauling was permitted between 9 p.m. and 7 a.m.

To complete the project without a serious casualty is nothing short of remarkable. To complete it on time and on budget is mind-numbing. Remember, this is Caltrans we're talking about -- the same agency that delivered the Bay Bridge 10 years late and $5 billion over budget.

The reason for the contrasting outcomes can be traced to the input of the Contra Costa Transportation Authority and the Alameda County Transportation Commission, which were deeply involved in project oversight.

"People think of it as a Caltrans project, but it was really a partnership," said Randy Iwasaki, executive director of the Contra Costa Transportation Authority. "Caltrans had the minority share of money in the project. The way the agreement read, we were on the hook for the last dollar. If that project ran over, my taxpayers would have paid for it."

Some $124 million of the $417 million price tag came from Contra Costa's Measure J sales tax measure; $180 million from federal stimulus funds; and $50 million from bridge tolls. The state had the least skin in the game.

"The reason you get sales tax measures passed is you make commitments to voters that you're expected to deliver," Iwasaki said. "If I ever want to get another tax measure passed, I have to deliver on commitments. We watched this project like a hawk."

There was plenty to watch during the 39-month operation. The biggest worry was the unknown. Rock and soil conditions differ on opposite ends of the dig -- denser on the east and looser on the west -- with unpredictable variations in between.

"As an engineer," Iwasaki said, "you're always worried about whether the ground will react the way it's supposed to. You bore shafts and take soil samples, but they're still just estimates of what you'll run into."

Because of the potential for methane gas, special precautions had to be taken, which meant no internal combustion engines. Boring equipment was electric, as were the muck trucks that removed debris. Special flashlights were needed.

One of the most memorable days came when the two excavating teams -- one starting in the east, the other in the west -- finally met in the middle. With precision lasers pointing the way, they were almost perfectly aligned.

"If I remember correctly," Iwasaki said, "they were about 3 millimeters off."

Not that Highway 24 drivers will care, as they zip from Orinda to Oakland. Hey, it's just another tunnel. What's the big deal?

Contact Tom Barnidge at tbarnidge@bayareanewsgroup.com.