Does anyone have any knowlage of this and how extensive the system is. And are there examples anywhere else in the world?

Imagine for example they took the M8 in Glasgow and sunk it, the whole thing, the stretch of motorway from the M77 to the M80, just sunk it down and then knocked down the old road and built parks and regenerated the land to other uses, thats how big, probably even bigger than that in fact.

Yes its a huge idea and one that took a lot of planning and re construction

There is a thread here.

Simon

On a personal note, I visited Boston in Summer 1995 and would not recognise the place if I went back there now (which I'd like to). I might have a photo or two of the elevated section if I raid the family photo album... I recall coming out of the Sumner Tunnel (or was it Callaghan) and emerging onto the toll plaza which then proceeded into a free-for-all as about 5 slip roads opened up pointing every which way. Good fun!

From http://www.interstate-guide.com/i-093.html:

The Big Dig

The section in downtown Boston was reconstructed in one of the most expensive and dramatic projects in highway history. Known as "The Big Dig," upon completion the project sees the removal of the elevated "green elephant" through downtown (though part of the double deck in Charlestown will remain). Traffic is relocated to a system of tunnels, as well as a new 10 lane (six lanes northbound, four lanes southbound) cable-stayed bridge over the Charles River (plus the four-lane Leverett Circle Connector bridge). This new span replaces the original six-lane double decker bridge. More information is on the official website.

No ceremonies were held as the last section of new freeway for Interstate 93 opened to traffic. The December 20, 2003 completion of the southbound lanes through Interstate 93's tunnel marked the end of the $14.6 billion project. The often controversial project was $4 billion over budget, and the source of bitterness among residents and politicians the like. With roots stemming from 1987, the Big Dig even raised concerns of then President Ronald Reagan because of its overwhelming cost. Nonetheless, after years of construction, the Big Dig sees the removal of a city eyesore and traffic nightmare with the opening of two miles of underground roadway.

One and a half miles of green space will be found at the former location of the Interstate 93/Fitzgerald Expressway when all of the demolition work is complete. With the busy freeway underground, up to 8 acres of public park space will grace the city along the former alignment. Additionally land for new housing, shops, and cultural venues will be available. All in all 16 million cubic yards of dirt were excavated for the 7.5 miles that constitute the new tunnels created.

Unfortunately, the Big Dig has a lasting legacy. Its underwater tunnels have a tendency to leak (it will take ten years to fix the problem - by 2015 in some early reports), the project managers (Bechtel and Parsons Brinckerhoff) are accused of making decisions that resulted in extraordinary costs for the project, and the cost overruns have caused NBC News to refer to this project repeatedly on its "Fleecing of America" segment. For more detailed information on the Big Dig, we recommend the following sites:

• Official Site from the Massachusetts Turnpike Authority
• The Boston Globe Big Dig Report
• The History Channel Compendium on the Big Dig

Question - why did America insist on building its Interstates directly through the centre of every major city it could think of?

It'd be like the M5 running up Queensway and the Aston Expressway.....

That's a bit of a generalisation. Quite a few cities (e.g. Washington DC, San Francisco and NYC) opposed freeway construction through their central areas.

Because they were earmarked for the movement of military goods and evacuations (their official purpose was for defence in case the cold war got nasty). Ergo they had to head into cities.

Cities that aren't on a mainline interstate usually have a spur or loop to compensate.

Because Americans don't have a history of caring about their downtowns. It's beginning to slowly change now, but for decades almost all road building was undertaken to benefit the middle class resident in the suburbs. If a few old neighborhoods get destroyed in the process of making a surburbanite's commute a little easier, then so be it- at least that was the attitude.

Actually, in all fairness, it was also that Americans had the huge wads of cash required to build urban motorways in the 1950's and early 1960's, whem the idea of urban motorways was really in vogue. By the time that Western Europe and the U.K had fully recovered from WWII and had the money for such schemes, the political and social winds had changed, people had seen the problems in the U.S., and therefore there weren't built to such a great extent. As for NYC, only in Manhattan did they have some success in opposing Expressways across Midtown and Lower Manhattan, Manhattan still got ringed (The West Side Hwy was shut down due to neglect, so it is no longer the case). The other Boroughs are criss-crossed by expressways and motorways. A large part of SF's urban motorway fell down during and after the 1989 earthquake, and was deliberately not rebuilt.

Actually, the opposition worked outside Manhattan too. Hence no Bushwick Expressway. Even projects which would have caused virtually no disruption, e.g. the Willowbrook Expressway, often got canned. The only really shocking example of strong community opposition being totally ignored was the Cross Bronx Expressway. One extremely controversial* explanation for that one is that the community was poor and black.

* i.e. it's probably true, but the political establishment deny it vociferously.

Tonight's episode of "Megastructures" on five at 8pm is all about the Boston Big Dig.

Thanks for the heads-up.

Did anyone watch this - found it to be very interesting, showing the challenges the engineers faced over the 13 year construction programme.

Must have a look and see if there are any online photos.

There are squillions if you know where to look, a80

I watched it too - very interesting documentary on the problems and solutions to both financing the project (originally conceived c.1975!) and constructing it. Boring an 8-lane (D4) expressway under hi-rises built on landfill (the move a mountain into the sea type, rather than the move garbage into a big pit in the ground type) or demolishing any buildings en-route (either intentionally or not!) must have been a huge challenge.

So, fantasy underground London Ringways anyone?! Financing it would be slightly more difficult than Boston (understatement of the century?), let alone all the legal/political arguments over getting it built.

Crossrail's taking long enough, and it's been in the pipeline for about the same time at the Big Dig too.

I saw it, a truly fascinating insight of the construction.

The challenges they faced, and overcame, like the uninterrupted running of everything around it, like the Underground railway, were tremendous. Particularly the cock up where the sunken tunnel sections were 3'6" too short

IMO that's the price you pay when you insist on working in f@$!ing imperial

Question - they replaced a massively congested D3 with a shiney new D4 tunnel. How long until thats also clogged up?

An amazing project though.

Ian - day one. The traffic around Boston would probably require at least D6 to be freeflowing.

The best they could do is sign traffic around the city, but the bypass routes are also clogged to buggery...