Tunnels

Posted by PITHOCRATES - January 22nd, 2014

Technology 101

A Bridge is a Fixed Structure that requires no Active Systems to Function

Bridges are dumb.  While tunnels are smart.  You can build a bridge and walk away from it.  And it will still work.  That is, you can still cross the bridge without anyone at the bridge doing anything.  It can even work in a power outage.  Even at night.  It may be dark.  But a car’s headlights will let a person cross safely.  Because a bridge doesn’t have to do much for people to use it.  All it has to do is stand there.  A tunnel, on the other hand, needs smart systems to make the tunnel passable and safe.

Bridges are high in the air.  Where there is plenty of fresh air to breathe.  If there is a car fire on the bridge all of that fresh air will allow other drivers to breathe as they drive around it.  And for first responders to breathe as they put that fire out.  They can use all the water they bring onto the bridge, too.  Even in a driving downpour.  For that water will just run off of that bridge without causing a drowning hazard.  Visibility doesn’t change driving onto or off of the bridge.  Unlike with tunnels.  Where you can go from bright daylight into a dark hole.  And from a dark hole into bright daylight.

A bridge is a fixed structure that requires no active systems to function.  Just some maintenance.  Painting and roadway lighting.  Maybe some traffic control signals.  But that’s about it.  Tunnels, on the other hand, need machinery.  Equipment.  Systems.  And people.  Because tunneling below grade causes a whole host of problems.  Problems that have to be addressed with machinery, equipment and systems.  And if they don’t work people can die in a tunnel.

Powerful fans at each end of the tunnel pull in fresh air and blow it through the duct under the roadway

Cars have internal combustion engines.  They exhaust carbon monoxide after combustion.  Which is poisonous if we breathe it.  A big problem in tunnels filled with cars with internal combustion engines.  Which is why if you look at a cross-sectional view of a tunnel you will see that the biggest section of these underground structures are used for moving air.

If you have driven through a tunnel you probably remember driving through a rectangular tube.  Little bigger than the vehicles driving through it.  What you don’t see is the air duct beneath the roadway.  And the air duct above the roadway.  Powerful fans at each end of the tunnel pull in fresh air from the atmosphere and blow it through the duct under the roadway.  It exits the duct at about exhaust pipe level.  This fresh air blows into the rectangular tube where cars are pumping in carbon monoxide.

Other powerful fans are also located at each end of the tunnel that pull air out of the tunnel.  Via the duct over the roadway.  Fresh air comes in from below.  Mixes with the poisonous carbon monoxide.  This gets sucked into openings overhead.  Into the duct over the roadway.  And vents to the atmosphere at either end of the tunnel.  Allowing these poison-making machines to travel underground in an enclosed space without killing people.

A Tunnel is a Complex Machine that requires Intelligent Programming not to put People in Danger

Tunnels through mountains go through porous rock that drip water into the tunnel.  Tunnels under bodies of water are low in the middle and high at the ends.  Making each tunnel portal a massive storm drain when it rains.  And water in a tunnel is a dangerous thing.  It can freeze.  It can get deep.  It can cause an accident.  It can drown people.  So when it enters the tunnel you need to pump it out.  Tunnels have storm drains that drain any water entering the tunnel to a sump at a low point.  And pumps move this water from the sump out of the tunnel.

Ever spend an hour or so shoveling snow on a bright day?  And then go inside only to temporarily lose your vision?  This is snow blindness.  Your pupils shrink down to a tiny dot outside to block much of the bright sun and the light reflecting from the snow and ice. And when you walk inside that tiny dot of a pupil won’t let enough light into your eye so you can see in the reduced lighting level.  After awhile your pupils begin to dilate.  And you can see.  Same thing happens when driving into a tunnel.  Of course, temporarily losing your vision while driving a car can be dangerous.  So they add a lot of lights at the entrance of a tunnel.  To replicate sunlight.  And as you drive through the tunnel the lighting levels fall as your eyes adjust.  At night they reduce the lighting levels to prevent blinding drives as they enter.  And prevent snow blindness when exiting the tunnel.

A bridge doesn’t need any of these systems.  But a tunnel won’t work without them.  As people could die in these tunnels.  Because it’s dangerous when people go below grade with machines that create poison.  So tunnels need computers and control systems.  To monitor existing conditions such as exterior lighting levels, carbon monoxide levels, smoke and fire detection, water levels and high water alarms, etc.  Based on these inputs a control system (or a person) turns lights on or off, increase or decrease supply and exhaust fan speeds, pump down the sump when it reaches a high water level, etc.  Only when these systems are on line and operating properly is driving through a tunnel as safe as driving over a bridge.  Because bridges are dumb things.  They only need to stand there to work.  While a tunnel is a complex machine.  That requires intelligent programming not to put people in danger.

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