Shock-absorbing Air Bag System to Reduce Railway Pedestrian Fatalities
First version: 10/14/2009. Last update: May 22, 2010
physics for a front-of-locomotive air bag appear feasible. The next
investigative task is to develop a
"sketch design" addressing various issues such as "hinging upwards." If a feasible
sketch design arises, then a follow-on investigation should estimate cost and ascertain whether it
is practical to prototype the design. Should the air bag system eventually prove
viable, it will take considerable time to bring about a wide-scale
In the US in 2006, there were 500 fatal
collisions between trains and pedestrians. Of these 500, about 360 were
suicides (see article below). Additionally there were about 300 fatal
collisions between trains and cars/trucks. Railway pedestrian collisions are also an international
A series of high schoolers
in Palo Alto have committed suicide via Caltrain commuter rail near Charleston and East
Meadow intersections. Psychologically speaking, these are
“dramatic” suicides where less-dramatic suicide methods would not be
substituted. In the first 11 months of 2009, there have been 14 Caltrain
pedestrian fatalities, some accidental and some intentional.
Exhorts Mark Simon, Caltrain Executive Officer
for Public Affairs, "We wish you well in your efforts to provide a
reliable and available means of preventing rail fatalities. Fatalities on
our right of way are a continuing source of concern at this agency and I
can attest that every death on our system ripples through this
organization and impacts all of us. We will follow your progress with keen
In addition to Caltrain, Amtrak Capitol Corridor intercity passenger rail
experiences multiple fatalities from accidents/suicides per year. See this
article about the spike in Bay Area fatalities:
There have been 9 Washington DC metro suicides in 11
The UK Rail Safety and Standards Board estimates
the total cost of suicides (trackside and at stations) to the UK rail industry
in 2003 was more than 11M GBP, @ 61,000 GBP per suicide. This includes delay
to trains, lost working time as a result of trauma suffered by staff and the
equivalent value of trauma as a minor injury. (RSSB – 2005 Annual Safety
Performance Report). BBC, Nov 11, 2004, "Each year 200 people end their
own lives on the UK's railways. ... it highlights the very real problem of
suicides on the UK's rail network."
Last year, nearly 2,000 people committed suicide
in Japan by jumping in front of a train.
Germany experiences roughly 936 railway suicides
Roughly 23 combined Toronto TTC subway and Go
Transit commuter rail suicides per year:
Air Bag Concept:
Imagine that the truck is a locomotive and the car
is a pedestrian. #23 is a 5-foot-long air bag system
#6106038: "System for Collision Damage Reduction:"
believes that his 5-foot-long, front-facing exterior air bag system allows a
driver to survive a 45-mph collision between the driver’s 3,000 lb car and an
immovable wall. The inventor calculates based on 18 g’s of
deceleration, although others point out that humans can withstand stronger
hints at a longer air bag system with higher crash capability. A collision
between a 200 lb human and a 60 mph locomotive changes the physics requirements
compared to the 45-mph car/wall collision. The inventor envisioned his invention
being applied to trains and buses, as well as cars.
appears to have considered and addressed many design challenges. The design is
much more complicated than a typical inside-the-vehicle air bag system. A
special, extra-strong air bag fabric is used. The venting system is clever: the
“collidant’s” velocity drops off exponentially with each additional foot of air
bag compression. To ensure that the air bag doesn’t pop, blowout patches relieve
the pressure. An inside-the-vehicle air bag fills and deflates rapidly. The
inventor’s external air bag stays inflated until the collision occurs. A radar
or sonar sensing system is used to detect an imminent collision and initiate
inflation of the air bag. The inventor creates downward pressure to keep the air
bag from hinging upward. A system of air bag compartments is used.
envisions a very low cost per vehicle, but experts are skeptical. A Federal Railway Administration staffer guessed at an “acceptable
budget” of $10,000 per locomotive for an air bag safety system.
For a 60 mph
locomotive colliding with a 200 lb pedestrian, a calculation of a 7.5 foot
air bag is given below by David Maymudes. This is a "promising" mathematical
conclusion - the abstract collision physics are feasible. The question now
becomes, is there a feasible, practical, low-cost design? Design issues include:
a) preventing the air bag from hinging upwards, b) selecting an air bag
design/fabric that won’t pop when pressed to the train tracks, c) meeting the
requirements of commuter rail operators, d) preventing pedestrians from getting
their ankles caught, e) how to fund, develop, and test a prototype, etc.
Inventor: Peter Dreher.
Air Bag Concept:
Principal Engineer, TRW Automotive: "I believe that this concept is possible.
I believe that it would take quite a bit of development due to the volume of
the 'bag' and the volatility of the propellants commonly used in air bag
systems. We would need to perform a lot of experimentation but I overall I
think it can be developed."
Maymudes explains the collision physics math for a 20g deceleration solution for
solution should exert a near-constant decelerating force, which is more the
case for things that are "crushable" rather than "springy."
physics standpoint, there's the question about how long it takes to safely
accelerate somebody from 0 to 60mph; at 1g, it's about 3 seconds, so at 20 g
it's 1/20th of that, about 0.15 seconds. During that time the train travels
about 15 feet; assuming constant acceleration, the person's "average velocity"
will be 30mph, since they're changing from 0-60, so during that same time
they'll move 7.5 feet, so you need 7.5 feet or so of "crush distance" to allow
them to move that much less than the train is moving.
the "save," the pedestrian is safely cradled in a crushable substance,
traveling at 60mph along with the train until the train slows. Some mechanism
/ property of the solution could work to keep the pedestrian safely in place
until the train stops.
be difficult to make this work perfectly at all possible orientations of the
body in question.
comments about Peter Dreher's design:
A human can
stand much more than 18g's in most cases. 64 g's is more like a fully fatal g
For a train,
I would imagine that a pre-inflated air bag would be easier and cheaper than
inflating the air bag when a collision is imminent. Keep in mind that a gas
generator is an ordinance device and can kill you if you get the gas pressure
edges of the safety zone would be more of a design factor than a middle of the
sweet spot hit, so the shape of the air bag may not be a simple wedge but it may
take on a hammerhead shark kind of look to get all persons in front of a moving
train to be safely caught by the device. I am sure you want to catch the person
not shove them to the side where there is a great risk of fatally hitting
something near the train tracks.
I also would
not suggest that an air bag inflate just in time because of the cost and danger
of the hot gas generator. On a train there is no cost penalty for having the
protection mat already inflated or foam rubber-like materials already in the
I would also
suggest that you do want an upward force as the deflection occurs because the
last thing you need it to run up on the body and trap it down as you roll over
the body. Getting enough up force but not enough to reach the windshield would
be a design requirement.
comment of the train air bag patent drawing. The side metal bars would be
dangerous if the object to be caught was not centered in the bag. This needs to
do more good than harm so the metal side apparatus needs to be rethought.
I would add
front wheels to this bag and make it longer so you are not pushing the limits of
human endurance. Once you have spent the effort and money to have a soft catch
you might as well make it a few feet longer to be easy on the body. Longer would
make the up-force vector have a wider design window too.
reasons I would recommend a pre-inflated structure or a plastic collapsible
structure so the dangerous hot gas generator explosive is not required. It works
on the car steering column because it is mandated but a lower cost solution is
to skip the instant inflation requirement in favor of full sized ahead of time.
I would also push for a much longer, wheeled car that is coupled to the train
and rolls on the tracks to maintain its vertical axis alignment. There is
nothing on the train tracks ahead or behind the train so a permanently deployed
bag or collapsible structure can lead and end every train including the slow
ones. A small embedded controller could take an active roll in grabbing the
pedestrian rather than expecting a static device to keep the distraught person
Walter Brewer's comments and calculations: a) The
air bag catcher has
to be designed to hold the person/object in place while the train decelerates
for several seconds. Otherwise it is back to the sweep aside case. Taking a
somewhat less lawsuit-vulnerable 20 g. the capture to a 60 mph train requires
about 6 feet. It increases as the square of the train speed. That assumes a neat
control of the body deceleration to a constant 20 g. If the air bag volume, or
equivalent, is large compared to the body that is probably doable. A linear
build up of air bag force would require longer distance before the 20 g peak is
For a constant 20 g acceleration; V squared = 2 x acceleration x
distance. (32.2ft/sec squared = 1 g.)
Thus at 60 mph: 88 sq = 2 x 32.2 x 20 x distance. (88 ft/sec = 60 mph)
Distance is ~ 6 ft.
This is in respect to the train of course to bring the body up to train
For the time required: Distance = 1/2 x 32.2 x 20 x time squared. Thus:
time sq = 6 divided by1/2 x 32.2 x 20. Time = 0.14 sec.
Train will have traveled 0.14 x 88 = 12 feet in that time.
Tom Rubin: a) I’m someone who has worked with
railroads quite a bit, and a change of this type will be slow to bring about.
At an absolute minimum, we’re talking years of research and development, then
tests on test tracks, and then a pilot program on “real life” engines.
Difficult and expensive – but, I think, well worth looking into. If this air
bag system concept fails utterly, it will likely do so fairly quickly into the
testing, so the cost might be no more than a few million to get to the point
where there is either a reasonable chance of something that could work and
have a significant positive impact on rail safety, or not. b)
I agree as to the air bag technology and would like to see the technology
developed further. Other than cost, there are not a lot of reasons not to deploy
them (you do need to make sure that only the bags on the front of the lead car
are deployed, and you need to make sure that they are not triggered
unintentionally, particularly by maintenance personnel, but these should be
Advanced Origami folding behavior may have applications in air bag engineering,
especially for this challenging application:
A Rough Sketch of One Possible Implementation:
The locomotive is 15' tall. The inflated air bag is
15' long by 7' tall. The person is 6' tall:
In the processing of the collision in 0.15
seconds, the top portion of the air bag deflates faster than the bottom portion.
Hence, for a standing person, the top of the body moves forward faster,
resulting in the body position rotating to be nearly prone. Slight air bag
hinging lifts the feet up off the ground:
(Source PPT for these rough sketch graphics:
Other Air Bag
|Ford has revealed plans for
external air bag "future technology for protecting pedestrians and other
vehicles during a collision. An over-the-hood air bag offers protection
to pedestrians, and occupants in other vehicles." (Car Design News, May 2001).
See picture at right:
May 2009, Autopia, "Researchers at Cranfield
University in England have developed an external air bag they say will
significantly reduce pedestrian fatalities and injuries in the event of a
See the two patents below.
The Mars Pathfinder external air bag system was
designed to protect the 264kg Lander from a 60 mph collision with a
planet. Development of the air bags required significant design and test
work. The air bags are made out of a high strength fiber called Vectran.
See also United States Patent 6883631,
External air bag occupant protection system.
See also the dvice.com article entitled
"External air bag armor protects vehicles against blastwaves." "While the
shrapnel created by a roadside bomb or improvised explosive device is
lethal all on its own, the concussive force of a blast can seriously
injure, incapacitate and kill the crew of a vehicle right through its
armor. To combat the effect of blast waves, a company called Survival
Consultants International has developed a wall of air bags triggered by a
light sensor. Light, the company maintains, is the only thing faster than
a concussive wave caused by an explosion. In a split second, the triggered
sensors confer with an on-board processor on whether or not to deploy the
bags, which in turn combat the force of a blast wave."
An “advanced transit
inventors web forum” brainstormed some possible solutions:
#6293205: "Train collision system."
train collision system helps reduce the severity of impact between a train and a
land vehicle or pedestrian. The system uses a flatbed rail car that is coupled
to the front of a train. Several deformable barrels, each at least partially
filled with an inert material, are attached to the top." Inventor: Paul A.
|US Patent #6474489,
A train collision attenuator mounted on a leading end of a train for
attenuating the force of impact between a moving train and a pedestrian or
motor vehicle. The train collision attenuator includes an energy absorbing
assembly and a mounting assembly. ... A selectively-inflatable,
externally-mounted air bag including an upper pedestrian cushioning portion
and a lower pedestrian support portion is also provided. Inventor:
Thomas S. Payne (Union City, CA)
compressed air "megagust" concept to reduce damage to the locomotive:
"I've worked with compressed air before and am
convinced a jet air blast could blow most organic objects off to the sides of
the rails before they made contact with the engine. Even large animals, like
moose, while still afoot, could be turned off the roadbed by an assisting
megagust." Fred Harrison Central Point, OR CORPpower/JSS/EORS
There is a well-known phenomenon known as a
“suicide magnet” or "suicide cluster" – where a location and/or a methodology
where one suicide occurs becomes a trigger for others with suicidal tendencies.
The best known in the world is the Golden Gate Bridge, with over 1,200 known to
date. Other notable “suicide bridges" include the George Washington Memorial
Bridge in Seattle, the San Diego-Coronado Bridge, the Sunshine Skyway Bridge in
Saint Petersberg, the Cold Spring Canyon Bridge in Santa Barbara County, the Van
Stadens Bridge, near Port Elizabeth in South Africa, the Bloor Street viaduct in
Toronto (500 people), and the Hornsey Lane Bridge
in London. The Eiffel Tower and the Empire State Building were also very well
known as suicide magnets prior to specific mechanical barriers being put in
place. In Japan, there is the “Aokigahara hanging forest” bordering Mt. Fuji,
which averages about 80 per year.
One frequent question is, if they want to commit
suicide, won’t they just go someplace else? Well, perhaps, but there does appear
to be reason to believe that attempting to put in a barrier at specific
locations would have at least some effect – in any case, if the “suicide magnet”
effect may be going on, it is reasonable for responsible individuals to at least
make responsible efforts to stop such suicide efforts at the specific location
where it is occurring. In Palo Alto, volunteer and professional security vigils
are in place to deter incidents.
In another example, amidst numerous cliffs in
Ireland, a single cliff became a spot for frequent suicides. A priest stopped
the trend by holding vigil at that particular cliff. Local citizens stopped
committing suicide and did not substitute other cliffs. [Thanks to Tom Rubin and
Doug Solomon for this section.]
One conclusion from a study of folks who survived
Golden Gate Bridge jumps. On the way down, they all concluded that they wanted
The Psychological Toll on Railway Operators
operator does not want to experience fatal collisions. Speaking as someone who
was responsible for both safety and human resources at the Southern California
Rapid Transit District in LA when we opened the Long Beach Blue Line, the most
dangerous light rail line in the U.S., this was, and is, a huge problem.
Unfortunately, the way the human mind works, it is very common for the last
thing that a person about to be run into by a vehicle sees is the eyes of the
operator of that vehicle, looking right at them.
I am told that this is not anything that one forgets, no matter how long it has
been, and no matter how much one tries, and no matter how much counseling one
In this situation, you never, NEVER, NEVER let the operator go back on duty. The
way that the rules go, the operator must immediately get a test for substance
abuse, which is a good excuse for getting them out of there as soon as the
on-site investigation is initiated. You then attempt to get them to counseling
as soon as possible. You generally try to get them to take some time off before
getting back to operating a vehicle in transit service, if at all possible. Keep
in mind that, under the bargaining unit agreement, if the operator wants to go
back to work, unless there is a specific physical reason not to allow it, they
can go back to work. For some, I am told, this is not a bad thing, but, at a
minimum, supervisors are asked to keep an eye out – which is difficult to do, as
operators work alone and generally have very little contact with anyone else,
particularly rail operators, who work in an enclosed compartment with no
After having spent too many hours at too many crash sites, all I can say is, be
careful out there and respect those railroad warnings; they are there for a
See also the
article "Death on the tracks: For Caltrain crews, trauma of suicides may never
go away." From the article: "One of the things that really sticks with an
engineer is the sound of striking somebody. It just is a very distinct, hollow
sound, and it's got a metal ring to it. The other thing is this feeling of
helplessness. When it's an obvious suicide and somebody is putting themselves
out there, there is nothing you can do."
One U.S. Rail Pedestrian Suicide per Day
Published Tuesday, November 24, 2009, by KCBS
Radio AM 740.
National Suicide Study Examines Tragedies in Palo
Alto, By Matt Bigler
More Americans are killing themselves on train
tracks. That's the finding of a new national study on suicides. The study
includes a close look at a recent suicide cluster in Palo Alto.
In the past six months, four students at Gunn
High School have taken their own lives at or near the same Caltrain crossing in
Palo Alto, what Karen Marshall with the American Association of Suicidology <http://suicidology.org>
calls a suicide cluster. "A larger than expected number of suicides in a short
period of time in the same place," she described. A study of suicide clusters in
Palo Alto and Washington DC recommends restricting access to problem train
crossings, with barriers or thorny bushes.
Local authorities, however, have been somewhat
resistant to that, pointing the finger instead at reporting on suicides. "By
showing videos of the passing train, the loud train steaming down its corridor,
we make it more accessible in the minds of someone else who's feeling troubled
or feeling depressed," suggested Dan Ryan with the Palo Alto Police Department.
The suicide study finds that every week, 7
Americans end their lives by jumping in front of trains.
Federal Research Proposal for Transit
Cooperative Research Program (TCRP)
research "problem statement" is being developed. For TCRP program details,
Federal Research Funding Sources:
an air bag engineer steps forward as a Principal Investigator, pursue the March
2010 federal TRB Innovations Deserving Exploratory Analysis (IDEA) funding round
(both for Transit IDEA and Safety IDEA).
http://www.trb.org/IDEAProgram/Public/IDEAProgram.aspx. Public entities
should provide letters of support.
the TRB Studies and Special Programs Division conducts policy studies at the
request of the U.S. Congress, the executive branch agencies, states, and other
sponsors. A group of public entities can run an idea up the political hierarchy
to secure such funding.
Stimulus II funding could be applied.
more freight rail pedestrian fatalities than passenger rail fatalities because
there are a lot more freight trains, although the passenger trains tend to be
more concentrated where there are people, for obvious reasons.
79 mph is the
maximum operating speed for almost all rail service outside of the northeastern
communication has been made with: Caltrain, Amtrak Capitol Corridor, City of
Palo Alto, design firms (IDEO, Mindtribe, Makani Power [air bag expertise],
Mission Motors, Humcycles), Stanford Design
Program, UC Berkeley SafeTREC (Safe Transportation Research and Education
Center), Pasadena Art Center College of Design (automotive design, industrial
design, etc), National Transportation Research Board committees: Commuter Rail
Committee and Rail Operations Safety Committee, DVExperts, Federal Railroad
Administration Office of Safety, inventor Peter Dreher, TRW's Vehicle Safety
Bosch Palo Alto Research Lab (Bosch makes air bags), and UK Rail Safety and
Standards Board (RSSB).