What About Emergencies?
Transportation Tunnels vs Surface Freeways
Emergencies happen and any well thought out system must anticipate and solve emergencies before they are encountered in the real world system. Transportation tunnels are no different. But first we should compare the safety of travel in the new transportation tunnel systems in contrast to travel in the existing system of surface freeways.
In tunnels and on surface freeways, accidents can happen. Tires can blow out, vehicles can catch on fire, a wheel can fall off and cause a crash. Tunnels are not immune to all problems. But it is worthwhile to ponder the types of crashes that are possible.
For starters, on a surface highway it is possible for two cars travelling in opposite directions to crash head on into one another. Within single lane tunnels, this category of crash is impossible. There is no head on traffic to interact with. Tunnels in this regard, therefore, are safer than surface highways.
Within the tunnels there are also very few places where any part of the tunnel can be run into. 99% of the tunnel is comprised of just the tunnel walls. A car could scrape against the walls as it screeches to a stop, but it cannot run into a stationary object like a power pole for example. Within tunnels there will be exits, and the exit will present a “Y” like split to the tunnel. A car could crash head on into the center of the Y if it failed to follow the tunnel exit to the right, or the main tunnel on the left.
This is no different from an exit from a surface freeway. We have developed collapsible guard rails to place at the exit ramps to safeguard people who crash there.
Overall, tunnels are far safer than surface highways or freeways as far as crashes are concerned. But, tunnels are more dangerous when it comes to fires, so fires must be considered carefully. Let’s consider one historic tunnel fire to understand why this is so.
Mont Blanc Tunnel Fire
In March of 1999, a semi truck travelling through the Mont Blanc tunnel from Chamonix, France to Italy caught fire. Expecting to be able to extinguish the fire, the driver came to a stop in the middle of the 7.2 mile long tunnel. But when he stopped the truck, the fire rapidly grew in size and could not be extinguished.
The fire quickly spread into the combustible cargo, 9 tons of margarine and 12 tons of flour. The burning cargo increased the intensity of the fire and quantity of smoke generated. Fires in tunnels are inherently dangerous because they consume oxygen with only the ventilation to replace it.
This means that the fire causes the atmosphere in a tunnel to become oxygen deprived. This in turn causes the smoke to be rich in carbon monoxide, a toxic gas. While the Mont Blanc tunnel had successfully dealt with around 35 fires over the years, this fire generated an unusually large amount of smoke. The smoke was so thick that vehicle engines that require oxygen, ceased to run.
This stranded people in their vehicles that couldn’t run and also prevented fire rescue trucks from reaching the fire. The rescue trucks engines ceased to function in the thick smoke. 39 people perished in the disaster. The temperature in the tunnel reached around 1,800 F. The tunnel had become a kiln. It took 5 days to cool down enough that workers could enter the tunnel. The remains found had been reduced to bones and ash.
If the fire and rescue vehicles had been battery electric vehicles, they would have been able to reach the fire and to rescue people stranded in the tunnel.
There were a number of emergency shelters throughout the tunnel. These were designed to shelter people for 2 hours during a fire. Some had been upgraded to shelter people for 4 hours. But it took 5 days before workers could enter the tunnel after this fire.
Clearly, something better than what they had must be created if transportation tunnels are going to be used. The longest Transportation Tunnels are expected to be cross country tunnels around 3,000 miles long. Compared to this tiny 7.2 mile long tunnel, the new technology will require a completely new method of dealing with fires and accidents within the tunnels.
Safety Measures
Transportation Tunnels will employ a variety of new features to insure the safety of people using them. They will be different in several important regards. Unlike the Mont Blanc tunnel that penetrates through a mountain, Transportation Tunnels are typically built just below the surface, following existing surface freeway routes right of way.
Because of the proximity to the surface, rather than building shelters for people to hide in for a couple hours assuming a fire can be quenched, Transportation Tunnels will be able to construct escape routes that bring people to the outside in case of an emergency.
If a tunnel escape stairway will be built every 200 meters or so, the longest distance anyone would need to walk to escape during an emergency would be 100 meters. Escape paths could of course be built at any intervals deemed safe by authorities. Typically, the road deck within a transportation tunnel will be around 15 feet below grade.
Once one exits a tunnel door, they will immediately be on the fresh air side of the door, out of whatever emergency is taking place within the tunnel. Even someone in a wheelchair could exit the tunnel through an emergency door, pull and emergency call button and help would arrive to get them away from whatever was happening inside the tunnel.
Battery Electric Fire and Rescue Vehicle
In the Mont Blanc tunnel fire, Italian fire / rescue vehicles made it to within 300 meters of the burning truck. They were able to see the flames, but, the heavy smoke incapacitated their vehicle and they could not reach the fire and could not fight it. If they had battery electric vehicles, they would have easily reached the fire and been able to fight the fire to extinguish it.
Instead, all fire fighting attempts failed and the fire had to be left to burn itself out. That took 53 hours. 5 days later, the tunnel had cooled enough that people could enter to assess the damage.
It turns out that there is a new way to fight a fire and this new way is especially useful in fighting a tunnel fire. Any fire, house fire, forest fire, tunnel fire, requires 3 things. Fire requires fuel, oxygen, and heat. Normally fire fighters combat a fire by working to cool it using water. If you cool the seat of the fire, you extinguish smoke generation and you can kill a fire.
But a fire can also be extinguished by removing the oxygen. In fact, it can be faster to remove the oxygen than to try to cool the fire. In some computer rooms this is accomplished by flooding the room with an inert gas such as Halon. When the oxygen concentration drops from 21% atmospheric levels to below 15%, the flames will immediately extinguish. A fire generating megawatts of heat release will instantly extinguish and be generating zero heat.
Humans require 12% oxygen concentration. So it happens that we can both extinguish a fire and at the same time, continue to sustain life.
Halon is expensive but there is another inert gas that is not toxic to humans, namely, water vapor. By spraying water droplets into a hot environment and causing them to vaporize, the volume of water vapor shot into a fire environment can be huge. Within 7 seconds water mist shot into a large 2 car garage can suffocate the flames filling the structure. Another 60 seconds later and the materials will be cool enough to no longer re-ignite the smoke into flames.
In a tunnel where oxygen is already reduced in concentration closer to 15%, dropping the concentration below 15% will be even easier.
A battery electric rescue vehicle will therefore be easily able to reach any fire because it does not require oxygen for it’s engine to operate. With this understanding, let’s now consider a couple ways to deal with specific emergencies.
A Flat Tire or a Crash
When a vehicle becomes disabled, it will stop inside the tunnel. The first thing the computer navigating a vehicle will do when disabled, even before stopping, is to send out an emergency SOS message to the tunnel operator, a computer system. That system will immediately notify all affected vehicles of the emergency and will direct all vehicles to take evasive / protective, action.
Cars ahead of a disabled vehicle will continue on their journey. Ahead of the disabled vehicle the tunnel will be emptied. Behind the disabled vehicle, following vehicles will come to an emergency stop either due to notification by the tunnel operation system or simply due to seeing the disabled vehicle ahead slowing down within the tunnel.
After slowing and stopping, all vehicles behind the disabled vehicle will back out of the tunnel via the closest exits. Emergency vehicles will enter the tunnel from ahead of the disabled vehicle after it is empty. The typical emergency vehicle will be equipped with a fork lift on front to simply lift the vehicle up and then carry it out of the tunnel. If the disabled vehicle is a high speed truck, the process will be more involved but essentially the same. It will be removed from the tunnel.
Following vehicle removal, the tunnel will be cleaned and all vehicles will be notified that traffic is resuming. For a simple flat tire, vehicles will be instructed to wait as the vehicle removal should take less than 5 minutes to complete, after which time the tunnel traffic can begin flowing again.
This will be possible due to stationing emergency rescue vehicles about every 5 to 10 miles down the length of the tunnel. Like fire departments, the rescue teams will be on call. They can double as emergency rescue teams for the local communities within which they are based.
As for a crash, suppose a tire falls off of a vehicle and it veers into a wall of the tunnel. It will scrape the walls and come to a stop. The same rescue process and vehicle will be dispatched, the same fork lift will lift and remove the vehicle, and the same cleaning crews will clean debris within the tunnel to put it back into operation as quickly as possible.
Dealing with a Vehicle on Fire
Now that dealing with a flat tire and a crash for any reason are understood, and now that issues associated with tunnel fires like the Mont Blanc tunnel fire are understood, we can describe how to handle the worst of situations. Suppose a tire falls off, a vehicle crashes, and a fire breaks out within a tunnel. What can be done?
The first thing to understand about Transportation Tunnels is that they have blowers that blow air down the tunnel at 90MPH in the forward direction. What this means is that any fire will have plenty of air to burn the fuel. But it also means that people in vehicles behind the disabled vehicle will be exposed to fresh air, not smoke filled toxic air as was the case in the Mont Blanc and other tunnel fires.
If the smoke is not too thick, the rescue vehicle can safely enter the tunnel from ahead of the disabled vehicle and remove it using the fork lift as before. Even though the vehicle is in flames, the forks can lift and or simply drag the vehicle out of the tunnel as quickly as possible.
Given the rapid response time expected, this should always be the case. Nationally, fire houses are positioned throughout communities with an expectation that they will reach a fire within 9 minutes and 20 seconds of being called. It took 26 minutes for the Mont Blanc fire team from the Italian side to get to within 300 meters of where the truck was on fire. The smoke was so thick, though, that they never reached the fire to try to fight it.
Within Transportation Tunnels, there should never be a situation where the smoke is so thick that a fire / rescue vehicle entering from ahead of a disabled vehicle is unable to reach the vehicle and extinguish the fire or remove the vehicle from the tunnel by using a fork lift or by simply dragging it out of the tunnel while fully engulfed in flames.
However, if we imagine that the smoke is so thick that a vehicle cannot drive to the fire location from ahead of the vehicle, then the rescue would need to wait for the vehicles behind the disabled vehicle to clear out of the tunnel. This will take several minutes longer for vehicles to back up. But the command to do so will be sent immediately upon notification that a vehicle is disabled within the tunnel. A fire / rescue vehicle should be able to enter from behind the disabled vehicle within about 5 minutes of the original SOS call.
This is because behind the vehicle, the air will be clear due to the blowers blowing air forward through the tunnel. The removal and clean up of the vehicle / tunnel would then proceed the same as before. Perhaps 10 or 15 minutes would elapse between the original SOS call and putting the tunnel back into normal operations.
Imagining even more improbable circumstances, we could imagine that a long line of vehicles suddenly all burst into flames and must be abandoned. In this highly dubious scenario, people would need to exit their vehicles and seek emergency exits to get out of the tunnel. With exits located so that the longest distance to an exit for any vehicle is just 100 meters, escaping the tunnels would be easy to do even if we assume an absurd fire scenario.
Earthquakes
When one ponders the safety of tunnels, the idea of an earthquake tends to cause fear. It turns out, however, that tunnels are actually among the safest places to be during an earthquake.
If the tunnel is built anywhere except where a fault crosses the tunnel, it will normally survive without damage. It’s a bit like trying to crush an egg in your hand. Squeeze as you might, equal pressure all around the egg shell makes it virtually impossible to crush.
It is possible, however, that a transportation tunnel may be constructed such that it crosses a fault. Whenever this is the case, then on the rare occasions when that fault slips, it will likely cut the tunnel. The first vehicle to encounter the damaged tunnel may crash. This is especially possible if the vehicle is close to a location where the tunnel is sheared at the same moment that the earthquake strikes. The computer driver of the vehicle will react much faster than would a human driver. Still, there may not be time enough for the vehicle to stop prior to reaching a place where movement of the entire earth sheared the tunnel.
Even before stopping, the vehicle computer controller will send a warning to the tunnel computer operation system and that will in turn send emergency messages to all vehicles in the tunnel system including the information on where the damage to the tunnel occurred. As with any emergency, all vehicles will be directed to exit the tunnel so that workers can repair the damage.
Workers will then assess the extent of the damage and repair it. This could mean sweeping up some debris or it could mean closing that section of tunnel for a longer period of time to effect repairs. In case of the latter, vehicles could exit the tunnel, commute on the surface freeway and re enter the tunnel beyond the damage.
While no where on earth is truly safe during an earthquake, tunnels are among the most safe places to be. Tunnels are far safer than being in a building above ground for example.
Conclusion:
Transportation Tunnels are among the safest ways to travel from one place to another. For this reason it is expected that they will be constructed around the world to eliminate traffic congestion and to speed travel of people and goods.
Every mode of transportation has its own issues to deal with and Transportation Tunnels are no different in this regard. But considering the high speed of travel combined with the near impossibility of having a dangerous accident, Transportation Tunnels are perhaps the safest mode of travel yet devised by mankind.