Our goal is to furnish you with the most accurate train performance information available. Our computer programs, book and paper on emergency braking with how to calculate stop distance are now available. 

                                                       Computer Programs  

                                                         (See description below)

            FREIGHT TRAIN EMERGENCY BRAKING                                 $650.00 U.S.




*Our computer programs are currently being upgraded. Some compatibility issues have been     encountered with new printers and computers so our programmer is modifying them. Freight is ready. Passenger is underway. As soon as he finishes them, he is going to do our master program. It has freight train emergency braking, service braking at all reductions and independent braking.   

 Hopefully it won't take long.*



       TRAIN DYNAMICS, INC.,  110 Shady Lane,  Perryville, AR, USA  72126-9696

            501-333-2788       Fax 501-333-2299       E-mail: jb@train-dynamics.com

“For expert testimony on train performance call 501-333-2480”



    Scroll down the web pages to find your desired topic.


      I. Programs

     II. Background

    III. Car vs Train

    IV. An Introduction To Train Brakes

    V. Derailments

   VI. Suggested Interrogatories & Production Of Documents





The “Freight Train Emergency Braking” and “Passenger Train Emergency Braking”. These programs will let you determine speed from stop distance or stop distance from speed as well as time for the stop. They are straightforward programs requiring minimal train knowledge. You can also determine the ability of the train to change its arrival time by an earlier application of the brakes in any distance,  giving you the new time and new speed at the end of the distance for comparison such as in a crossing accident. These programs have been used by the defense in State and/or Federal Courts in AR, CA, CO, FL, LA, NM, TX, and by the plaintiff in AR, CA, CO, FL, IL, LA, MO, OK, TN, TX, VA and WV. They have never been excluded. These programs are being used by the  NTSB, engineers, law enforcement, colleges, railroads and attorneys. If you’re dealing with accidents involving trains, the data provided could only be enlightening. 

These programs are straightforward requiring minimum skills. You just enter the information it asks for on your train. If you do not have all of the information, a list of suggested entries is furnished to allow you to get a very close evaluation until you get the accurate information. Once you have the data entered, you can then run the speeds from 1 to 100 mph to obtain the brake distance in feet and the brake time in seconds. Once you have done this, you can then determine how much the train could have delayed its arrival at the incident by an earlier application of the brakes. 






The principal developer of the software has attended both A and B schools with the Texas Highway Patrol, the Law Enforcement Academy with the U. S. Department of Justice and is a graduate of the Traffic Institute at Northwestern University. He was with the Texas Highway Patrol in the 50’s and 60’s as an expert in accident reconstruction. In the mid 60’s, he left the Department to enter a private consulting practice and to assist Missouri Pacific and Southern Pacific in the defense of crossing accidents. Wheel/rail adhesion, wheel/shoe adhesions, AB valve timing and propagation rates were obtained from the manufacturer. Time segment methodology was established to determine an accurate stop distance with elapsed time. This was verified with a test train from Santa Fe in 1971. It was verified again in 1975 with a test train from Southern Pacific. In the 80’s and 90’s, many tests and comparisons with event recorder outputs were made with trains from Missouri Pacific, Union Pacific and Burlington Northern. The time segment method equations were then programmed to develop a computer program on braking at all levels using these empirical results. After 35 years, evaluation testimony in over 1200 cases, he has decided to make this available to the public.




Car Versus Train


John Bentley

Copyright 2003

  What does your car mean to a train? Lets see. The car today weighs about 3,500 pounds or 1.75 tons. The typical coal train has 6 power units at 200 tons each and 115 cars at 120 tons each. The train weighs 15,000 tons. Lets assume the train is traveling at 55 mph. The car speed is 0 mph in the train direction of travel. If we multiply 55 x 15000, we get 825,000. Now lets divide this by the weight of the car and train combined. We get 54.9936 mph for the train after impact. Your car slowed the train .0064 mph. As you can see, your car was insignificant to the train. Now lets see about you. If your car was struck near center, you get about 2’ of crush on the car. With the train at 55 mph, this will take .0248 second. If we divide the train velocity of 80.667 by this time we will get an acceleration rate of 3,253 feet per sec/sec. Since 1g is 32.16 feet per sec/ sec, this is an acceleration rate of 101 g’s. Your weight is 1 g due to the acceleration of gravity. This means that if you weigh 150 pounds, you will have a minimum force placed on your body of 15,150 pounds. This is like having 4 of your cars stacked on top of you. The force on you will actually be higher as the car starts accelerating before the side of the car impacts you so you will accelerate in a shorter distance. One other thing of interest, today’s cars have your head about the same height as the coupler on the train. This coupler extends about 2’ in front. It comes right through the window and hits your head. Your head goes to 55 mph almost instantly. People very seldom survive this type of accident. Always look both ways before you enter a railroad crossing. The life you save may be your own. Comments or questions: jb@train-dynamics.com 




An Introduction to Train Brakes

By John Bentley  

Copyright 1999


Imagine a vehicle that is a mile in length. It is so long that the front of the vehicle might be climbing a grade while the back is descending, or perhaps the front and back are turning left while the middle is turning right. This same vehicle is more than 500 times as long as it is wide. Next, imagine that it weighs more than 8 million pounds or 4000 tons. Onboard the vehicle, there are televisions, foodstuffs and hazardous material. Now, visualize the vehicle is traveling at 60 MPH and the operator wants to stop.

This is a complex and challenging problem, but a situation that occurs thousands of times every day. The vehicle of course is a typical freight train. This short paper will introduce the reader to the principles of how train brakes accomplish this remarkable task.


Freight train brake systems have not changed in basic operation since the 1930's. They are controlled and actuated by compressed air. For those tempted to think that train brakes operate the same way as large truck brakes read on. You might be surprised.

Each power unit (locomotive) has an air compressor that supplies air for the entire train's braking system. A feed valve in the locomotive regulates the desired pressure that is supplied to the train. This pressure must be at least 70 psi (although most modern systems use 90 psi). A "brake pipe" runs the full length of the train. The brake pipe carries the compressed air from the control unit to the rest of the train. Unlike truck brakes (and passenger train brakes for that matter) this single source of air carries both the air that powers the brakes as well as the signal to control them.

Details of Brake Operation

Each rail car has its own brake system. The brake components include a brake cylinder, brake shoes, a dual air reservoir, and a control or AB valve. The AB valve is used to route air from the reservoirs (auxiliary and emergency) to the brake cylinder. The brake cylinders are connected through rods, levers and slack adjusters to the brake shoes. Train brakes are normally off, or unapplied. The return spring in the brake cylinder is used to return the piston and pull the brake shoe away from the wheel and allow the wheel to roll freely. So, in order to apply the brakes, air must be ported from the reservoir to the brake cylinder.

There are several ways the engineer can apply braking to the train. He selects the type of braking depending on the nature of the stop desired.

SERVICE BRAKING: This is the type of brake application normally used for slowing or stopping. This level of braking is achieved with a 6psi to a 26psi reduction in the brake pipe pressure. When the AB valve senses the difference in pressure air is ported from the reservoir to the brake chamber. Air pressure acts against the piston and brakes are applied. Braking with the Service Brakes offers up to 75% of a train's emergency brake capability.

INDEPENDENT BRAKES: These are the brakes on the locomotive units only and do not apply brakes on any of the cars. While this brake method would effectively slow the locomotives if operated alone, this type of braking has only a minimal effect on a fully loaded train. These brakes are used in train handling, standing or any time a small brake level is needed on a train. They can give a braking level from none up to full independent, which is 75% of the locomotive's Emergency Brake capability.


Flexible Hose Carries the Brake pipe between Cars 


A Brake Cylinder and associated Hardware


A Brake Shoe Removed from its Retaining Hardware and Held Against the Braking Surface of a Wheel


POWER BRAKING: This means just what it says. When an engineer anticipates a problem may develop or desires to control the speed of the train, an application of the service brakes is made without reducing the throttle. When the train has slowed or the problem does not arise, then the train brakes are released and the train continues on, with the throttle still set. This type of braking has the advantage of reducing the time necessary to achieve Emergency Braking. This results in a quicker stop than an Emergency stop that was not preceded with Service Braking.

DYNAMIC BRAKING: This is using the traction motors of the units in a reverse flow so that they act to slow or stop the train. This type of braking is used primarily for train handling as it only slows the train via the locomotives. This type of braking cannot compare to train brakes.

EMERGENCY BRAKING: This is all the brake capability that a train has. It is utilized, as implied, when there is an emergency. Application of Emergency opens the brake pipe to atmosphere on all cars and units sequentially from front to rear. As a result, the AB Valves ports pressure from the Auxiliary and Emergency reservoirs to the brake chamber and all brakes slow the train. This type of brake use applies the brakes as fast as possible. An emergency application will cancel throttle to idle (see Power Braking above).

Special Considerations

Utilizing air brakes on a vehicle that is more than 1 mile in length poses some interesting problems. Under ideal circumstances the air signal travels at about 921 fps. This occurs in emergency, when the brake pipe is vented to the atmosphere. Thus, if a train were 5,526' long, it would take 6 seconds for the last car to sense the pressure drop and begin to start applying the brakes. The Federal Railroad Administration, under CFR Part 49, specifies the maximum time each car can take to achieve maximum braking. On trains operating at 70psi brake pipe pressure this maximum application time is 10 seconds. So, our hypothetical 5,526' freight train would take 16 seconds to attain full emergency braking. During these 16 seconds the train will have steadily increasing brake application taking effect between 1.5 (the time for braking in the first car to begin) to 16 seconds (the time the last car achieve full braking).

A second counter-intuitive situation exists with train brakes. Reconstructionists are accustomed to ignoring vehicle weight when calculating stopping distances. This assumption has validity for vehicles that skid to a stop. Trains on the other hand are designed with a maximum brake force that is below the force necessary to lock the wheels of an unloaded train. The effect of this is that maximum braking force is the same for loaded and unloaded trains and stopping distance is roughly proportional to weight. Stated another way, a train weighing twice as much will take about twice as far to stop. While this idea may be counter intuitive, it of course makes perfect sense for a vehicle with fixed maximum braking force.

Finally, train acceleration rates are severely restricted when viewed from a road vehicle's perspective. Cars and large trucks are capable of stopping at nominal rates of .75g. This stopping force originates at the tire-road contact area. It is limited by the friction coefficient between these two surfaces, rubber and asphalt, rubber and concrete, etc. All of these surfaces have dry surface friction coefficients near .75. Just like road vehicles, trains gather their slowing force from the wheel-track contact area. A typical friction coefficient for steel on steel is .25. This value is near the value of rubber on ice. So, it is not improper to view trains as perpetually driving on a surface that is equivalent to ice. The actual slowing or stopping is controlled by the wheel/shoe adhesion. A train can stop up to 40% shorter in distance using wheel/shoe adhesion rather than steel wheels on steel rails. The wheel/shoe adhesion drops off rapidly as speed increases. The result is, when compared to road vehicles, trains change their speed very slowly. Despite the fact that a train reacts slowly, an engineer does have the ability to make meaningful changes in speed that could result in avoiding a collision. The following example will detail such an analysis.

A Typical Grade Crossing Analysis

An example of a time distance analysis follows. In this case a train was approaching a road crossing at 29 M/H. The sight distance available to the engineer was 484'. The question posed is how much could the engineer have delayed the train's arrival at the crossing by placing the train in emergency? That analysis follows.

Total Available Distance = 485'

Initial speed = 29 M/H (42.5 ft/sec)

Estimated reaction time = 1.5 Seconds


Number of units (Locomotives)

= 2

Length of units (Locomotives)

= 136.66 feet

Weight of units (Locomotives)

= 350.5 tons

Number of cars

= 18

Length of cars

= 902 feet

Gross weight of cars

= 980 tons

Empty weight of cars

= 540 tons

Train length

= 1038 feet

Gross weight of train

= 1330 tons

Empty weight of train

= 890 tons

Brake pipe pressure

= 90 psi

Emergency propagation

= 1.128 sec.

Emergency braking efficiency

= 0.736


= -.00173

First lets determine the Engineer's reaction distance using an average reaction time of 1.5 seconds.

Reaction distance = (Reaction Time) x (Velocity)

Reaction distance = (1.5 seconds) x (42.5 ft/second) = 64 feet.

Subtracting this reaction distance from the total distance of 485' leaves 421' feet for the train to slow.

Next let's determine how long it would take the train to arrive at the crossing if the engineer did not act.

Distance/Rate = Time

(421 feet) / (42.5 ft/second) = 9.89 seconds

Next, we must calculate the actual slowing for the train. This is not a simple calculation. Recall we must account for the time for the air to propagate the length of the train. Next, the actuation time of the brakes for each car must be considered. We must also determine the weight of the train then compare it to brake force. The results of these calculations will be presented in the table below without support.

Initial Speed (mph)

Stopping Distance (feet)

Time to Stop (sec)





The first thing that is apparent is that the available stopping distance of 421' is well less than the 712.1' feet required for the train to stop. The conclusion: The train can't stop before it gets to the crossing. But perhaps more interesting is the comparison of the time it takes the train to reach the crossing with and without braking. Again, this involves detailed calculations beyond the scope of this treatment. The result will be presented for purposes of comparison. Given the 421' brake distance the train arrives at the crossing at 24.14 M/H. The time it arrives is 10.46 seconds after the point the brakes were first applied. This time should be compared to the time required to reach the crossing if no action was taken. That time calculated above was 9.89 seconds. The difference is .57 seconds. This difference in time is not much, but perhaps sufficient for a car to clear the crossing.


When compared to other modes of ground transportation trains have some unique characteristics that require special analytical consideration. The length of a train and its associated pneumatic brake systems, determining the train weight and calculating brake force are all variables that appear in stopping distance calculations. While running steel wheels on steel tracks greatly increases a train's load-carrying capability, these materials limit the ground forces available so that speed changes in trains occur relatively slowly.

These problems notwithstanding, this truly massive vehicle travels thousands of miles daily with infrequent incident.

John Bentley is a former Texas Highway Patrol expert in accident reconstruction. In 1964, he entered into a private consulting practice. This practice steadily evolved toward train specific accidents and is now limited to train performance. He has participated in train testing, developing parameters, training and is a frequent lecturer on the topic.

Mr. Bentley can be contacted at jb@train-dynamics.com







John Bentley

Copyright 2004

    Most freight train derailments are caused by improper train makeup. A properly made up train will have the loaded cars behind the units and the empty cars behind the loads. Under this makeup, an engineer can safely make an emergency application of the train brakes. Most of the time, the train can have a collision and not derail if the units do not derail. If loads are placed behind empties, then when emergency braking is used or a collision occurs, the units have full braking efficiency and retard. The loads have a reduced braking efficiency and move in on the empties. The old squeeze play. The empties are in the middle. Since the empties only run 20-30 tons, the ends will raise off the trucks and jackknife. If the engineer is aware of the improper makeup, he will bail the brakes on the unit to reduce the holdback of the units and hope that it works. In most cases,  it doesn't. This can also occur in hills where the train is stretched pulling the loads up over the crest then the loads start downhill and run in on the empties which are held back by the front portion of the train going up the next hill. If the train is properly made up, look for speed too great for a curve as there may be high center of gravity cars with a speed restriction on them. 

A derailment which is common to both freight and passenger trains is rail buckling. This is common with the continuous welded rail. This is most frequent with a cool or cold night and then the temperature climbing rapidly causing the steel rails to expand quickly. Occasionally, this will cause a rail to buckle. If it buckles inward, a wheel flange will climb it and derailment occurs. If it buckles outward, the wheel will drop down off the rail and derailment occurs.

These are the most common types of derailments. There are others.  Comments or questions: jb@train-dynamics.com  If you need an evaluation of a case, call 501-333-2480. Fax 501-333-2299





John Bentley

  1. Furnish a copy of the ADVANCE CONSIST for this train. 
  1. Furnish a copy of the ACTUAL CONSIST for this train at the time of the accident.
  1. Furnish a copy of the wheel report or work list for the train in this accident.
  1. Furnish a Marketing UMLER report on each rail car and locomotive in the train.
  1. State whether the lead engine was LEAD QUALIFIED at the time of the accident.
  1. State whether the lead engine met all FRA rules and regulations at the time of this accident.
  1. At the time of this accident, had the event recorder on the lead engine been BAD ORDERED?
  1. Furnish a copy of each event recorder output in the DATA TABLE format for the last five miles up to a stop at the crossing.
  1. Furnish the weight and length of each locomotive in the train.
  1. Furnish a list of the cars in the train from front to rear by identifying number.
  1. Identify by number each loaded car in this train with its weight at the time of the accident.
  1. State the brakepipe pressure or feed valve pressure setting for the lead locomotive.
  1. Furnish a copy of the first MECHANICAL INSPECTION REPORT made on each engine after the accident.
  1. State the trailing tonnage for this train.
  1. Furnish the track profile for at least two miles each side of the crossing.
  1. State the Milepost designation for this crossing.
  1. State whether the Mileposts increase or decrease in the direction of travel.
  1. State the identifying number for the crossing as registered with U.S. Department of Transportation.
  1. State the FRA class track at the accident location.
  1. Furnish copies of all SLOW ORDERS applicable to this train on the date of the accident.
  1. State whether any cars in this train were SPEED RESTRICTED.
  1. Furnish copies of all SPEED RESTRICTIONS applicable to this train on the date of the accident.
  1. State the identifying numbers of any cars carrying HAZARDOUS cargo.
  1. List the identifying numbers of all cars cut out of the air brake system of this train.
  1. State the speed the train was being operated at when it was placed in emergency.
  1. Who applied the emergency brakes?
  1. State whether the crossing is within YARD LIMITS.
  1. State the distance to the nearest YARD LIMIT each side of the crossing.
  1. State the maximum permissible track speed for this train at the crossing.
  1. Furnish copies of all TIME & DELAY REPORTS covering this accident.
  1. State whether the engine brakes were bailed with the emergency application of train brakes.
  1. Furnish all measurements made by anyone.
  1. Furnish all documentation which shows any FEDERAL FUNDING being expended on the crossing if you intend to exert U.S. Code Title 23, 45 or CFR 49 in your pleadings.
  1. Furnish the length of the train without the engines.
  1. At the time of this accident, state whether any Maintenance of Way operations were being conducted within ten miles of the crossing.
  1. Were there any speed restrictions for this train within ten miles of the crossing?
  1. State whether the long or short end of the locomotive was in the direction of travel.
  1. Furnish a copy of the Timetable applicable at the time of the accident.
  1. Furnish a copy of the Wire Report required and on file with the Superintendents Office and/or the General Claims Office.
  1. Furnish the distance from the accident to the front of the lead unit at stop and before being moved.
  1. Furnish the distance from the accident to the front of the train when the crew first saw the vehicle.
  1. How far was the vehicle from the crossing when it was first observed?
  1. What was the speed of the vehicle?
  1. What part of the vehicle did the train strike?

  2. Was this train equipped with an end of train (EOT) device which placed the rear of the train in emergency simultaneously with the emergency brake application on the front of the train?



     Questions or comments? Contact  jb@train-dynamics.com.





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