Throughout the 1990s and into the early 2000s, Boston boldly invested in itself. It cleaned up the harbor, spending $3.8 billion on the Deer Island Treatment Plant alone. It spent from $650 to $850 million, depending on how you count, in state money for the Boston Convention and Exhibition Center, said spokesman Nate Little. Fifteen billion dollars of federal and state money went to the CA/T project, aka Big Dig, which buried the Central Artery and created the Ted Williams Tunnel.

These efforts, mostly completed by 2004, have paid off in improving Bostonians’ quality of life. We can swim in Boston Harbor without worrying about the “floatables” that sailed past when a friend of mine finished first in the 1977 Boston Light Swim. While our underground automobile trip through the Financial District is little faster than when we took the overhead road, neighbors no longer have to see or hear the stalled traffic. Instead we can take a beautiful walk through a maturing Greenway. Boston turned around and became the waterfront city it had been and was meant to be

Charlestown gained two lovely parks instead of the overhead tangle where I-93 and I-95 once met in possibly the most difficult intersection ever of two interstate highways. (We taught a daughter to drive by guiding her there from Leverett Circle, theorizing that she’d better know how to drive like a Boston driver.)

North End and Waterfront residents are no longer cut off from the rest of the city by an overhead road. And the rest of the city can now get to those neighborhoods with pleasure.

In anticipation of the Big Dig, utility companies relocated and upgraded underground connections, giving Boston a competitive edge over other older cities, recalls Bob O’Brien, who lived through it all when he served as executive director of the Downtown North Association.

The whole thing has provided an astounding boost to Boston’s economy. The Boston Convention and Exhibition Center, along with the Back Bay’s renovated Hynes, will contribute $750 million in benefits in fiscal 2017, said Little. The BRA calculates that projects approved since 2005 in the Seaport District total more than $6 billion in investment.

I’ve made my own calculations along the Big Dig with O’Brien’s help. In the dozen or so years since public projects were completed, private real estate investment totaling about $15 billion has built buildings or has them under construction or planned around the buried Central Artery. (If you want my list, email me at Karen@bostoncolumn.com, and I’ll send it to you.) That figure includes such projects as the InterContinental Hotel, built around a tunnel vent tower, the proposed Haymarket Hotel, and the condominiums at Boulevard. That project, which adds the phrase, “on the Greenway” to its name and famously incorporates one standing wall from an original Bulfinch building is one of several projects not starting from scratch. Minor changes—cutting windows into the side of buildings that once lay next to the highway, changing doorways so outdoor restaurants now spill out toward the Greenway—are small contributions to the economy that I’ve not included in my tally.

How much can be attributed to the Big Dig? A good economy and the fact that Boston’s industries are the ones thriving everywhere today have helped. Nevertheless, O’Brien said, in the Downtown North area, alone he calculates that the Big Dig is directly responsible for more than $5 billion of investment. This includes parcels built on land freed by removing the elevated highway’s underpinning—the rental apartments on Canal Street, The Victor, Related Beal’s affordable housing on Beverly Street. Larger development sites at the Nashua Street Residences and the Boston Garden would have been less appealing if the overhead road had remained, he said.

“The depression of the Central Artery, which created the Rose Kennedy Greenway, was a major factor in the revitalization and redevelopment of the downtown waterfront district from the North End though South Station and it was unquestionably a major catalyst for renewal and redevelopment of both Downtown Boston and the West End,” O’Brien wrote in an email.

Not even the Great Recession slowed investment much.

Don Chiofaro said his team bought the Harbor Garage because of its location between the harbor and the Greenway. Tom O’Brien said HYM’s project from Cambridge Street to the Greenway was based on the aftereffects of the Big Dig. “It is absolutely true that the Big Dig made projects like ours conceivable,” he wrote in an email. “In fact, I would say the Big Dig helped turn the entire Downtown into a residential neighborhood.”

Other projects along the Greenway may have gotten built whether or not the road was buried. Perhaps the Seaport District would have occurred without the Ted Williams tunnel and the other two public investments, but I doubt it, and so does Chiofaro.

Chiofaro has been around a long time and sees the Seaport’s growth, in particular, as directly related to them.

Everyone is impressed with the speed at which the Seaport has developed, but it wasn’t speedy at all, he contends. “The fact is when I got out of high school in 1963, someone took me to Pier 4 and said this is the next great real estate opportunity,” he said. “I looked at the steel nets and asked, ‘What are those?’ They were the nets we used to close Boston Harbor during World War II.

“In 1968 when I got out of college, I was told that district was the next great real estate opportunity. Five years later I got out of business school and was told it was the next great real estate opportunity.

“Long story short is it didn’t happen fast. It took the momentum of the depression of the Central Artery and the cleanup of the harbor,” he said.

So now, when we’re complaining we don’t have enough money to build the Green Line extension, the train to the South Shore, the North-South Rail Link and other big projects, maybe we should look back at the 1980s leadership that got Boston into its happy situation today.

We’re a richer city and state than we were then. To say we can’t afford to make big investments in infrastructure is to not notice where it has gotten us before.