I live in Western Montana and there are more than a few instances where I have to wonder, while driving, why didn’t they build a tunnel here? It seems like in many cases they displaced quite a bit of material to make a cut, and the road still isn’t flat. Meanwhile, the railroad a few yards away goes through a tunnel.
I understand that trains can’t handle changes in topography as well as cars and trucks, and I’m not advocating I-80 be a sea-level tunnel between NYC and San Francisco, but still, I wonder why road tunnels aren’t more common. Wouldn’t it cut down on gas use, even if not by much? Are tunnels that hard to make?
My experience with Pittsburgh suggests that a possible reason is that drivers get nervous in tunnels and slow down for no appreciable reason, causing traffic backups for miles in the approach that dissipate literally instantly at the other end of the tunnel.
Train operators, being on tracks and not having to contend with other trains right next to them, are less likely to be affected by the kind of psychological factors that I imagine cause this in drivers.
I am not a tunnel expert, but they are very expensive, difficult and dangerous to build, and expensive to maintain.
The railroads have been “daylighting” them for about a century, tearing the roofs out of shallow tunnels because it’s easier to maintain them or they need to add a track.
Yeah, you have to remove a lot of fill, I would imagine, before it’s cheaper to make a tunnel. If it’s dirt or clay, tunneling is tough because supports are needed. If it’s rock, blasting is even more dangerous inside a tunnel than in a rock cut.
Plus, you’re likely making fill that you need for building up the approach anyway.
If you wish a case study in the political as well as engineering difficulties involved in tunnel construction, you may read about Devil’s Slide on highway 1 in California:
The Bay Area also has a tunnel called the Caldecott tunnel which carries route 24 under the Berkeley Hills. It was originally two bores, constructed in the 1930s, and carrying two lanes of traffic in each direction. In the 60s, they added a third bore. Since then, they’ve switched the middle bore between eastbound and westbound twice a day to accommodate the directions of rush hour traffic. Costs on tunnel construction are such that it was only in the last few years that they’ve started construction on a fourth bore, rather than fiddle around with that. The fourth bore is supposed to open in 2013.
Southern Ca could use a tunnel from Los Angeles to the Antelope Valley. It would have a serious impact on property values and development. Cost would be enormous.
Are there any tunnel experts out there? I drive through the rockies every now and then and there’s a mix of tunnels and really challenging ‘cut throughs’ (I don’t know the technical name for blasting through maybe a km of rock and putting a surface road through). A couple posters have stated that tunnels are:
a) more expensive to build than (say) cutting through a steep hill
b) more difficult than cutting through a steep hill
c) more dangerous to build than (say) blasting through rock to create a surface road
d) more expensive to maintain.
Mountainous roads are tough to build, too. I’d wager (but am by no means an expert) that it’s really difficult, dangerous and expensive to cut a road, build switchbacks and maintain in icy conditions a ‘conventional’ mountain road.
In terms of maintenance for roads inside tunnels, there’s no need for plowing and I imagine that the road surface needs less maintenance due to having a roof overhead. Although, the tunnel structure would need maintenance and lighting costs would add up. Anybody have any stats?
It definitely is, because there is rarely any space to the side for an emergency lane or in the middle for a median.
However, the emergency lane and median are also frequently missing in mountainous terrain and/or when they’ve had to cut through rock without tunneling. So it isn’t an exclusive danger for tunnels.
Excavating expense (more than $1,000 for every meter advanced and that’s just the bare excavation,) high maintenance cost, plus cheaper alternatives. Instead of cutting through the mountain, why not just cut along the slope following a contour line?
The same Caldecott Tunnel also illustrates another reason why tunnels can be dangerous: Certain accidents that may happen within them can be more dangerous if people get trapped. In April 1982, there was a multi-vehicle accident in the middle of the tunnel involving a gasoline tanker truck :eek:
Multiple vehicles got backed up behind the accident and couldn’t back out (because of other cars backed up behind them). When the leaking gasoline caught fire, they all became Caldecott Flambaise. Several people abandoned their vehicles and ran like hell, surviving with only a moderate char-broiling. Several others were thoroughly incinerated. (I’m remembering this from news articles of the time. The Wiki page describes the accident in rather less inflamatory terms.)
In the same year there was even greater devastation wreaked in the Salang Tunnel in Afghanistan, through which went the only road usable by heavy vehicles between the USSR and Kabul (IIRC). When the entire 2.6 km length of the tunnel was filled with two Soviet army convoys, an explosion smack in the middle detonated a fuel tanker, which detonated all the other fuel tankers. Mega-inferno throughout the tunnel’s length not only killed thousands, it must have taken them months to retrieve all the dead people and tow all the destroyed vehicles out, with Kabul cut off by road from Russia. The mujahidin claimed responsibility. Some say the Salang Tunnel disaster was the worst traffic accident in world history. But if it wasn’t an accident, it was an unusually effective strike in asymmetrical warfare.
Somehow I always think of that when I’m in the middle of the Allegheny Mountain tunnel.
I’ve done some digging (heh) and it seems like tunnels are generally more expensive than roads, but in certain situations, they are cost effective.
It seems like there’s just many more engineering challenges with putting a tunnel project together than a regular road. In my reading, I learned how important water is in tunnelling, something I hadn’t really considered. Dealing with water can be a huge challenge, as witnessed by Floater’s link.
Keep in mind, that there are many, many, many more miles of conventional road in existence than tunnels and so the techniques and engineering associated with them are well-known and developed. Tunnel bulding technology is still evolving and hidden price hikes still emerge.
The first time I drove across the mountainous region of middle Japan I was stunned by the sheer number of tunnels there are, ranging from 200 meter tunnels to 3 kilometer tunnels.
I drive the West Virginia Turnpike quite a bit. Just south of Charleston and old single-bore tunnel was replaced by a huge cut in the mountain and I was struck by the sheer volume of material that had to be removed compared to what had to be taken out in boring the tunnel. Could it be that modern earth moving equipment has changed the economics of tunneling vs. making a cut?