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Re: Vehicle Weight
Author: SP5103
Date: 02-24-2015 - 17:04
I agree the physics have changed due to more information becoming available. CNN claims the driver told police he became confused and drove 50 yards down the track before stopping, and tried calling 911 when he saw the train. Based on the location of the wreckage, I presume the vehicle was driving towards the train.
If the train hit the truck and trailer at near track speed (79?) on open track and then shoved it through the crossing, then the probability of the train staying on the track drops. Photos show the front of the truck destroyed and separated from the service bed, but the trailer is on the crossing with the island signal mast and gate mechanism wrapped into it. Remember that most highway signs, lights and signals are designed to break away when hit by a vehicle.
A train takes FOREVER to stop in emergency. I have been lucky in that my derailments/crossing collisions have all been at around 10 mph, and it still takes about 150 feet whether you are still on the track or not. The braking effort has an upper limit where the wheels will slide due to the lack of adhesion to the rail. Common railroad practice is for locomotives and passenger cars to have a high braking effort approaching the limits of normal adhesion. By comparison an empty freight car has about 1/2 the braking effort per weight, and loaded freight cars would have 1/4 or less. When moving engines and passenger equipment dead in train, you need to limit the maximum brake cylinder pressure or you will probably get flat wheels (though leaving the handbrake applied is also too common). While the heavier engine was pushing, it should have had the same braking ratio per ton as the passenger cars.
As far as the blended braking - there isn't any real consistency among railroads as to if the dynamics will continue to function in an emergency brake application. Obviously any throttle under power should have dropped out, but I have seen locomotives wired so that an emergency brake application takes out the dynamics, leaves them alone or allows their use under certain conditions. It may have been an advantage to have the blended brake, but I'm not aware if it would still have been functional in emergency.
The news continues to brag up these are new design safer cars, but the Bombardier car didn't seem to have been any more damaged on the outside compared to the Rotems. They all seem to have stayed intact on the major structure except for the draft gear. Would hate to see the insides though.
This brings us to a simple issue - physics are physics. The more survivable you try to make something typically the heavier it becomes which in turn increases the forces involved. Whether it's planes, trains or automobiles, at some point all the crumple zones and crash energy management engineering cannot deal with the energy created from greater speed and/or mass. Short of transporting passengers in a nuclear transport cask, at some point the only realistic survivability is to prevent any chance of the accident in the first place.
If the train hit the truck and trailer at near track speed (79?) on open track and then shoved it through the crossing, then the probability of the train staying on the track drops. Photos show the front of the truck destroyed and separated from the service bed, but the trailer is on the crossing with the island signal mast and gate mechanism wrapped into it. Remember that most highway signs, lights and signals are designed to break away when hit by a vehicle.
A train takes FOREVER to stop in emergency. I have been lucky in that my derailments/crossing collisions have all been at around 10 mph, and it still takes about 150 feet whether you are still on the track or not. The braking effort has an upper limit where the wheels will slide due to the lack of adhesion to the rail. Common railroad practice is for locomotives and passenger cars to have a high braking effort approaching the limits of normal adhesion. By comparison an empty freight car has about 1/2 the braking effort per weight, and loaded freight cars would have 1/4 or less. When moving engines and passenger equipment dead in train, you need to limit the maximum brake cylinder pressure or you will probably get flat wheels (though leaving the handbrake applied is also too common). While the heavier engine was pushing, it should have had the same braking ratio per ton as the passenger cars.
As far as the blended braking - there isn't any real consistency among railroads as to if the dynamics will continue to function in an emergency brake application. Obviously any throttle under power should have dropped out, but I have seen locomotives wired so that an emergency brake application takes out the dynamics, leaves them alone or allows their use under certain conditions. It may have been an advantage to have the blended brake, but I'm not aware if it would still have been functional in emergency.
The news continues to brag up these are new design safer cars, but the Bombardier car didn't seem to have been any more damaged on the outside compared to the Rotems. They all seem to have stayed intact on the major structure except for the draft gear. Would hate to see the insides though.
This brings us to a simple issue - physics are physics. The more survivable you try to make something typically the heavier it becomes which in turn increases the forces involved. Whether it's planes, trains or automobiles, at some point all the crumple zones and crash energy management engineering cannot deal with the energy created from greater speed and/or mass. Short of transporting passengers in a nuclear transport cask, at some point the only realistic survivability is to prevent any chance of the accident in the first place.
