U.S. Department 

of Transportation

Federal Railroad 

Administration 

_____________________________________________________________________________________________

Report to the Senate Committee on Commerce, Science and 

Transportation and the House Committee on Transportation and 

Infrastructure 

 

 

 

 

 

 

_____________________________________________________________________________ 

June 2005

Safe Placement of Train Cars: 

 A Report
1

Table of Contents

 

Introduction ........................................................................................................................... 2 

Train Make-Up..................................................................................................................... 4 

IN-TRAIN FORCES ....................................................................................................................... 4 

Excess train forces–steady state ............................................................................................ 6 

Excess train forces–transient................................................................................................. 7 

DIFFICULT CAR TYPES............................................................................................................... 9 

HARMONIC MOTION ................................................................................................................ 10 

RESEARCH ................................................................................................................................ 11 

FUTURE ACTIONS ..................................................................................................................... 13 

In-Train Placement of Hazardous Materials Cars...................................... 15 

Regulations ............................................................................................................................... 15 

Issues......................................................................................................................................... 17 

Research.................................................................................................................................... 18 

Conclusion .................................................................................................................................... 26 
2 

REPORT TO THE

SENATE COMMITTEE ON COMMERCE, SCIENCE AND 

TRANSPORTATION

AND THE

HOUSE COMMITTEE ON TRANSPORTATION AND INFRASTRUCTURE

Introduction

ection 111 of the Hazardous Materials 

Transportation Authorization Act of 1994 

(see box) requires a report on two related, but 

distinct, issues: first, make-up of trains in such a 

manner as to prevent derailments caused by intrain forces and, second, placement of hazardous 

materials cars in trains so as to avoid harm to 

crew members or interaction of hazardous 

materials, should a train accident or other 

unintended release occur. 

 Essentially, train makeup is not an issue 

that focuses on hazardous materials but on the 

distribution of power, braking effort, and weight 

throughout a train and the effect of each on train 

handling. From the point of view of train 

makeup, whether or not heavy cars belong at the 

front of a train is independent from whether or 

not those cars are carrying hazardous materials, just as, from the perspective of hazardous 

materials safety, whether or not hazardous materials cars belong at the rear of the train is 

independent from how many empty cars are in the front of the train. The reality, of course, is 

that both considerations are vital and FRA's (Federal Railroad Administration) stewardship of 

railroad safety requires that rules written in one area not overlap into another, to the detriment of 

either. 

 Train make-up remains a matter under active consideration by the FRA as this report is 

prepared. While this report provides the current status of our activities, analysis in this area is 

ongoing. FRA will continue to use data gathered in this effort in conjunction with all our data 

while making decisions about focusing our safety resources. 

S Section 111 of the Hazardous 

Materials Transportation Authorization Act 

of 1994 (P.L. 103-311) provides: 

SEC. 111. SAFE PLACEMENT OF TRAIN CARS

 The Secretary of Transportation shall 

conduct a study of existing practices 

regarding the placement of cars on trains, 

with particular attention to the placement of 

cars that carry hazardous materials. In 

conducting the study, the Secretary shall 

consider whether such placement practices 

increase the risk of derailment, hazardous 

materials spills, or tank ruptures or have any 

other adverse effect on safety. . . . 
3

 Train placement of hazardous materials has been thoroughly reviewed with appropriate 

consideration for possible regulatory change. For reasons set forth in this report, FRA currently 

sees no merit in disturbing established and very effective requirements already embodied in the 

Department of Transportation’s Hazardous Materials Regulations. Although there is a 

theoretical basis for adoption of various refinements to train placement requirements, in no case 

is it apparent that their implementation would offer advantages sufficient to offset the costs 

involved–particularly the safety risk associated with additional switching of cars. 
4 

Train Make-Up

rain make-up refers to the distribution within the train of railroad cars that are empty or 

loaded, short or long, or that have other characteristics affecting their ability to negotiate 

railroad track while subject to "draft" (stretching) forces and "buff" (compressive) forces within 

the train. Improperly assembled trains are more susceptible to derailment, depending upon 

grade, curvature, train handling (use of the throttle, independent brake, dynamic brake and 

automatic braking system), and other factors. 

 FRA has no regulations directly governing train make-up. Since the 1970s, FRA and the 

AAR (Association of American Railroads) have conducted extensive joint research that led to 

industry guidelines for track-train dynamics, including distribution of cars within a train by 

weight and other characteristics.1 The resulting book, the Train Make-up Manual, suggests that 

certain in-train configurations, combined with certain operating territory conditions, do not lead 

to problems. Essentially, according to that research, no 

special consideration for train make-up need be given for 

general merchandise trains composed of average length 

railroad cars2 where the total train weight is less than 4,000 

tons, the maximum gradient is less than 2 percent, and the 

maximum curvature is less than 8 degrees.3 Where the train 

exceeds 4,000 tons, long car/short car combinations are, 

ideally, to be restricted within the consist so as not to exceed 

maximum trailing tonnage for the ruling grade/curvature combinations set forth in the Manual. 

IN-TRAIN FORCES

 Understanding the development of the forces acting within a train4

 requires, in turn, 

understanding four factors that produce those forces: First, train resistance, or the force gained 

by adding grade resistance, curve resistance, acceleration (or deceleration), and rolling 

resistance. Second, tractive effort, or the force generated by the locomotive at the coupler to 

overcome train resistance. Third, braking, or the force necessary to overcome the momentum of 

 

1

 See, for instance, Lovette, P.M. and Thivierge, Train Make-up Manual, Report R-802, Association of 

American Railroads Research and Test Department, AAR Technical Center, Chicago, 1992.

2

 An “average length railroad car” is one 40 - 50 feet long.

3 Train Make-up Manual, p. 2.

4 Train Make-up Manual, pp. 3-9.

T 

AAR’s Vehicle Track Systems “noproblem” train: 

T Less than 4,000 tons total train weight; 

T Less that 2% maximum gradient; and 

T Less than 8E maximum curvature. 
5 

the train–whether from rolling inertia or down-grade acceleration–and to slow or stop the train. 

Braking is accomplished by dynamic braking, by use of the automatic brake, and by use of the 

independent brake. Dynamic braking is a process by which the traction motors are electrically 

converted to become generators. The current they develop is then dissipated, or “wasted,” 

through resistor grids. A very loose, imperfect analogy to dynamic braking is the use of engine 

compression braking to retard a car or truck as it moves down a hill. Because dynamic braking 

almost always starts from the head end of a train, the retarding forces will concentrate, or “pileup,” at the front.5

 The automatic brake controls the application, and release, of brake shoes 

against the wheels of a train, controlled by the operation of a brake valve in the locomotive. 

Once automatic braking has been established, retardation is applied to each car and there is no 

steady state concentration of braking forces in the train.6

 The independent brake controls brake 

applications at the locomotive only. As with dynamic braking, use of the independent brake 

causes retardation forces to concentrate at the front of the train. 

Slack represents the range of 

longitudinal travel of a coupler relative to the 

car to which it is attached. Most, but not all, 

common freight cars are equipped at each 

end with AAR standard knuckle couplers 

attached to the car through a “draft gear.” 

The coupler - draft gear system is designed 

so that the coupler may travel through a 

particular distance when a draft or buff force 

is applied to the coupler. A small amount of 

free movement is found between and within 

the couplers themselves, but most of the travel is found in and controlled by the draft gear. Draft 

gears are designed to permit that limited travel, and to control shocks by absorbing energy as the 

travel reaches its limit. 

 

5

 Of course, where mid-train auxiliary power is used, the forces from dynamic braking will “spike” behind 

each set of locomotives and where a rear pusher locomotive stays on a train as it moves down off the crest of a hill, 

the effect of its braking action, whether dynamic or not, will tend to create slack ahead of the locomotive.

6

 Brake application is not instantaneous throughout the train because the air “signal” that moves down the 

brake pipe travels at the speed of sound, rather than of light, the way an electric signal does. The signal takes 2-3 

minutes to travel the length of a 100-car train. While the brakes are applying, forces tend to concentrate at the head 

of the train, although mid-train power, helper engines, and two-way end of train brake devices, each of which can 

initiate a brake application from its location, are able to establish steady-state braking significantly faster than with 

head end power alone.

Development of slack as train length increases. 

TRAIN LENGTH TOTAL SLACK

50 cars 50 feet 

100 cars 100 feet 

150 cars 150 feet 

200 cars 200 feet 
6 

 Travel in one draft gear can reach six inches, depending on the force on the coupler and 

the rate of application of that force. The connection between any two cars may therefore 

contribute nearly twelve inches of slack, so that the total slack in a train may approach one foot 

for every car in the train. The cumulative amount of slack in a train is proportional to the length 

of the train. A 150 car train of common freight cars can have almost 150 feet of total slack. 

 

Draft gears are designed so that a locomotive starting a train will effectively start the train 

car-by-car, rather than starting the train as one solid mass. The standing inertia and friction in 

the wheels and bearings of a standing car is much higher than that of a car which is moving, even 

slowly. It is therefore necessary to “break the train loose” one car at a time to reduce the tractive 

effort and draft forces that would otherwise be required if all cars in the train were to be started 

simultaneously. Even with the force absorbing properties of the draft gear, a rapid rate of slack 

travel through a train can develop excessive draft or buff forces that could damage or derail the 

train. Some cars are designed with much lower coupler or draft gear travel, including such 

devices as sliding center sills or semi-permanent couplers without conventional draft gear, but a 

majority of common freight cars will permit the slack travel as described above. Conversely, 

some cars are equipped with end-of-car cushioning devices, which permit greater ranges of 

coupler travel than do conventional draft gears. 

Excess train forces–steady state

 Excessive train forces can break equipment, cause a rail to turn over, or cause a car to 

climb a rail. Steady state forces are those that are applied for a relatively long period of time 

such as the pull up a grade or the compressive forces of descending a grade under dynamic 

braking.7

 High steady state forces can cause three problems: 

Train separation occurs when unreasonably high draft forces exceed the physical 

strength of the materials used in a car’s draft system and the train breaks in two. 

The coupler knuckle is the intended weak link, to protect the draft gear and end 

sill assemblies. 

Stringlining, buckling, and 

jackknifing are similar 

phenomena, that is, reactions 

to forces that depend on the 

direction of the force. Draft 

forces below the maximum 

 

7 Train Make-up Manual, p. 10.

RESISTANCE OF

LOADED TRAILING CARS

TRACTIVE EFFORT ("PULL")

OF LOCOMOTIVE(S)

BRAKING EFFORT ("PUSH")

OF LOCOMOTIVE(S)

EXCESSIVE

RUN IN:

"BUCKLING"

EXCESSIVE

RUN OUT:

"STRINGLINING"

MOMENTUM OF

LOADED TRAILING CARS
7 

described above tend to stretch the train into a straight line, (a “stringline”) thus 

causing severe lateral loads along the inside of the curve. Track is designed to 

withstand these forces under normal conditions, but combinations of cars with a 

high center of gravity or with light loads may have a higher lateral load than the 

track or the car can resist. Several failure possibilities exist under these 

conditions: The lower rail may roll over, the whole track structure may be pulled 

from the ballast towards the center of the curve’s arc, the wheels on the high side 

of super-elevated8 track may lift and derail, or the cars may tip off the rail on the 

low side. It is even possible for the cars in the train to be “picked up” and 

deposited in the inside of the curve with few, if any, marks on the rails to 

determine the exact point of derailment. 

Buckling is the opposite of stringlining, where forces in buff cause cars to skew off the 

tracks. Both stringlining and buckling are aggravated when the cars under force 

vary between loaded and empty. 

Jackknifing, like buckling, happens when forces 

within the train act towards each other at 

levels greater than the vehicle/track 

combination can handle safely. Cars 

pushing against each other attempt to fold 

like a jackknife and coupler angles can 

create lateral forces similar to, but in the 

opposite direction of, stringlining. 

Typically, the rail car does not turn over (initially) but a wheel climbs over the rail 

or a rail turns over and eliminates the ability of the track structure to contain the 

train. Jackknifing is often exacerbated by combinations of long and short cars 

coupled together. 

 

Excess train forces–transient

 Transient forces, by definition of short duration, also play a role in optimizing train 

make-up.9

 They are primarily the result of train operations over changing grades or during 

acceleration or deceleration. The most certain way to avoid excess transient forces in terrain 

with a changing contour is to evenly distribute tonnage throughout the train; failing that, tonnage 

 

8

 Track is “super-elevated” when the outside rail is raised above the inside to compensate for the centrifugal 

forces of higher speed movements. 

9 Train Make-up Manual, p. 11.

RESISTANCE OF

LOADED TRAILING CARS

MOMENTUM OF LOADED

TRAILING CARS

EXCESSIVE

RUN IN:

"JACKKNIFING"
8 

should be concentrated at the head end. The worst case scenario places concentrated tonnage to 

the rear of empty or lightly loaded cars. A brief look at terrain features known to induce 

transient forces will further explain the potential dangers: 

Crests are changes in gradient from uphill to downhill, adjusting the free play (slack) in 

the train from slack-out to slack-in and causing a transient force to run through the 

train as the slack runs in.10 If the transient forces exceed the ability of the track 

vehicle system to contain it, cars may jackknife and derail. Crest transient forces 

are magnified by larger differences in gradient, higher train speeds, faster rate of 

brake application (train or dynamic) at the crest, and tonnage concentrated toward 

the rear of the train. A crest has the effect of adding the force of the cars toward 

the front of the train on the descending grade to the tractive force of the 

locomotive, so the cumulative forces might exceed the capacity of the draft 

system unless the locomotive tractive effort is reduced on the descending grade. 

Sags are the opposite of crests and cause slack to adjust from running-in to running-out. 

Excess transient forces here can break a coupler knuckle or, if the train is in a 

curve, derail a car by stringlining. Sag transient forces are magnified by the same 

conditions as magnify the forces induced by crests. 

Undulating terrain combines the worst of crests and sags and may place a long train in 

each such state at several points along its length. Optimum train make-up and 

skillful train handling are vital to safe and successful operations across 

undulations; power and brake applications must be small and gradual. Problems 

with pulling (draft) forces and pushing (buff) forces can also happen to trains 

where the cars are either all loaded or all empty. Experience with the Tropicana 

Orange Juice unit train and with unit trains of coal or grain proves the 

proposition.11 In uneven terrain (and railroads that are table-top flat are the 

extreme exception), the rolling of the land can induce significant draft and buff 

force peaks at almost any point in the train which, if they get high enough to 

overcome the inertial forces holding the train on the track, can lead to 

derailments. 

 

10 Ibid., p. 12.

11 Recognized references include: Powers, R.G. and Stephenson, J.G., "Train Action Measurements in the 

Tropicana Unit Train," ASME Paper No. 73-WA/RT-9, November 1973 and Fahey, W.R., et al., "Derailments on a 

Heavy Haul Railway," Session 315, Paper 3.4, Heavy Haul Railways Conference, Perth, Western Australia, 

September 1978.
9 

DIFFICULT CAR TYPES

 Certain types of cars,12 physically different from conventional cars, are known to require 

special consideration if they are to move over the road safely. “Difficult cars” can cause 

dilemmas even in AAR’s “no-problem” train. 

Multiple platform cars fall into two types: those with stand-alone two-truck platforms 

joined either by a drawbar or a non-operable conventional coupler and those with 

articulated platforms sharing a common truck. Both types have conventional 

couplers at the nether ends. Only the articulated platform cars require special 

analysis in train make-up; they require a consideration of trailing tonnage at the 

articulated connection between two platforms, at the coupler connecting two such 

cars, and at the coupler connecting a multiple platform car to a conventional car. 

The Train Make-up Manual includes formulas for making the necessary 

calculations (beyond the scope of this report) but the make-up problems are not 

the result of articulation but of light (empty) weight. The truck and car geometry 

of articulated shared cars are actually an improvement over conventional cars, but 

the reduced vertical loads increase L/V ratios and may be the limiting condition.13 

Single axle cars can be considered as normal cars 

when using the formulas in the Manual, but 

special note must be taken that these cars have 

extremely low light (empty) weights. 

Entraining them ahead of heavier cars may 

lead to adverse L/V ratios, as can sharp vertical 

curves common to crests in yards and at 

crossovers, which may contribute to wheel 

unloading. 

 

Long car/short car combinations can become critical in crossovers where there is less 

than one car length of track in between the lead curves of the switches, and the 

 

12 Ibid., p. 37.

13 “L/V ratios” are a calculation of the lateral (sideways) forces acting on a rail car divided by the vertical 

forces. Vertical forces are typically generated by weight, although there may be a minor, transient increase in V 

forces at the bottom of a sharp dip. As a gross over-simplification, where lateral forces exceed vertical forces, cars 

tend to be pulled (or pushed) off the rails.

L

V V

L
10 

dilemma gets worse the sharper the turnout. The problem stems from the long 

overhang of these cars, that is the distance from the truck center at either end to 

the coupler pulling face at that same end. Known problem areas are probably best 

handled by re-routing. The phenomenon is also critical on sharp curves, where 

the discrepancy in car lengths causes the coupler geometry to impart unusually 

high lateral and overturning forces on the joined cars. 

End of car cushioning is designed to reduce the shocks and resulting lading 

damage from high draft or buff forces, especially in rail yards. The detrimental 

effect of these devices on train make-up is the extra slack they contribute to total 

train length. No firm guidelines exist for optimizing operations in trains 

containing these cars, but some major carriers limit the number of EOC-equipped 

cars in a single block; another common practice is to entrain such cars after 

loaded cars with conventional draft gears. 

HARMONIC MOTION

 Train make-up may be influenced by three different types of harmonic movement, a 

condition very sensitive to train speed, but usually unaffected by train length or trailing tons. 

Truck hunting is an instability that usually occurs at speeds in excess of 45 miles per hour 

in cars that are empty or lightly loaded. Worn trucks can cause hunting as slowly 

as 35 miles per hour. This type of harmonic is observed as yawing and twisting 

of the carbody around the center of the car and it may cause sufficiently high 

lateral and low vertical forces to cause a wheel to climb up over the rail (wheel 

climb). The great irony of truck hunting is that it most often is worst on what 

seems to be the best track—tangent track with welded rail—and curves as low as 

one degree may suppress hunting. Poor track alignment and surface decrease the 

potential for truck hunting, but increase the likelihood of a derailment if a 

“hunting” car is in the consist. Certain car series are known hunting bad actors 

and most railroads maintain speed restrictions on such cars. 

Pitch and bounce tend to occur at speeds greater than 45 miles per hour and are seen as 

extreme vertical displacement at the ends of the car, with the ends of the car either 

in-phase (both rising at the same time) or out-of-phase (one end rises while the 

other falls) depending on whether the car is in pitch or bounce mode. Pitch and 

bounce are most often observed on loaded cars with insufficient suspension 

damping. Short cars such as ore jennies and a group of tank cars known 
11 

colloquially as “beer can” cars14 are more prone to this condition than long cars. 

Railroads maintain a list of such cars for review before a planned high speed 

operation. 

Harmonic roll is a low speed (10-25 miles per hour) harmonic motion associated with 

heavily loaded, high center-of-gravity cars on less than prime track. Sometimes 

called “rock and roll,” the condition happens most frequently on half-point 

staggered jointed rail where the truck centers of the car are close to the joint 

spacing. Because the classic rail length is 39 feet—the length that would fit in a 

40-foot gondola car—the typical “rock and roller” is a short 50-foot long, high 

sided, covered hopper car loaded with grain or other dry-flowing material. In a 

train handling such cars, harmonic roll can be effectively prevented by operating 

outside the 10-25 mile per hour speed range. 

RESEARCH

 The industry itself, through the Association of American Railroads, has continued 

research and evaluation efforts particularly related to new types of equipment as the equipment 

has been introduced. The AAR, through the Transportation Technology Center, Inc. (TTCI), has 

also continued to develop a computer-based model used to analyze and predict in-train forces, 

known currently as the Train Operations and Energy Simulator (TOES). 

 FRA’s Office of Research and Development is conducting a study of train make-up 

considerations. The goals of the study are: 

• assess train make-up guidance describing “good practice” as it is available in the open 

literature, 

• review individual railroads’ operating rules relating to train make-up, 

• review railroads’ train make-up practices in the field, and 

• review records of accidents attributed to improper train make-up. 

 In order to better understand the operating rules and field practices, the study has begun 

with a review and analysis of train accidents attributed to train make-up and train handling. 

 

14 They are short but maintain the same approximate diameter as a standard tank car and look remarkably like a 

very large version of their namesake.
12 

From here, it will move to a review of the written policy, as expressed in the operating rules, and 

the field practices. Finally, the research will “run” actual railroad consists on a train operations 

simulator to determine whether the particular trains could traverse varied terrain safely. 

 This research has been arrested by the unavailability of a suitable computer model for 

analysis of in-train forces. Although it has offered to conduct analyses for the FRA, AAR has 

declined to license the TOES model to FRA. AAR explains that control of the model is 

maintained “to ensure the model is run properly.”15 With encouragement from staffs of the 

NTSB (National Transportation Safety Board) and Transport Canada, in Fiscal Year 2003 FRA 

initiated development of a new computer-based model called ATTIF (Analysis of Train/Track 

Interaction Forces) to accomplish this work. The new model is being designed as a publicdomain code and will be available for use by other government agencies and members of the 

public. It is currently under development through a joint collaboration with the University of 

Illinois at Chicago. 

 During the initial development phase ending September of 2004, the structure of the code 

and the main subroutines required for solving the system equations have been fully generated 

along with detailed 3-dimensional elements for accurate prediction of wheel/rail contact and 

interaction forces. An algorithm for modeling braking and traction forces has also been 

developed and implemented within the new code. While generally similar in functionality to 

TOES, the new model, due to its advanced wheel/rail contact treatment, will allow for 

considerably more accurate prediction of lateral to vertical load ratios that are key for assessing 

derailment tendencies. This will also greatly reduce the time needed for conducting detailed 

safety studies where currently additional codes must be run in conjunction with TOES in order to 

generate the more accurate wheel/rail forces. It is anticipated that by the end of 2005, the new 

code will begin to be used for conducting safety and risk evaluations of various train operation 

and make-up scenarios. Other future potential applications include accident investigations, 

energy consumption and train operation studies, ride quality evaluation, as well as new and 

current equipment safety evaluations. 

 During the next phase, which began in October of 2004 and will end in September of 

2006, more detailed coupling elements such as draft gears, end-of-car cushioning devices, draw 

bars and articulated connectors will be developed and added to the code library and a more userfriendly interface will be added. 

 

15Letter of November 1, 2002, from AAR President Edward R. Hamberger to FRA Administrator Rutter.
13 

FUTURE ACTIONS

 FRA, the NTSB (National Transportation Safety Board), and the railroads continue to 

identify train accidents attributed to train make-up. In any given year railroads now report 

approximately 40 derailments using a train make-up “cause code,” down from as many as 80 in 

the early 1990's. These totals include code H599, “other causes relating to train handling or train 

make-up.” Over the period 1992-2002, these events resulted in approximately $37 million in 

harm to persons and railroad property (2002 dollars). Included in this amount are costs 

associated with no fatalities, five (5) injuries, and the evacuation of 2,300 people. A majority of 

these events occurred in yards,16 and two-thirds occurred on Class 1 track (maximum authorized 

speed 10 mph). It should be noted that the rate of these events has declined more steeply than 

their absolute numbers, given the growth in train miles over the period. 

 Additional accidents attributed to improper use of power brakes, improper train handling, 

and other causes may also be related in part to train make-up where the combination of grade and 

curvature together with less-than-ideal train make-up creates an excessive challenge for the 

locomotive engineer. On an annual basis over 100 derailments are reported under these cause 

codes. Although most of these events are minor in nature, over the period of 1992-2002 they 

accounted for $102 million in harm to persons and railroad property (2002 dollars). It is not 

known how many of these events, if any, might have been prevented with better train make-up. 

 Better train make-up practices may lead to further reductions in the train accident rate. 

However, in evaluating options for improved train make-up, it will be important to consider the 

costs, and especially the safety costs, associated with more extensive switching of cars. The 

most common cause of fatalities to railroad employees is being crushed or run over in switching 

operations. According to the Switching Operations Fatality Analysis (SOFA) Working Group, 

there were 114 such fatalities in the period 1992-2002. Although every effort is being made to 

reduce these numbers, and some success is being achieved, increasing the exposure of train and 

yard crews to these hazards should be carefully weighed. 

 Further reductions in adverse train make-up and train handling events are possible under 

existing rules and practices. More extensive use of empty/load brake valves (evening out the rate 

of deceleration of cars in the train when brakes are applied) and distributed power (with 

additional locomotives in the middle of the train under radio control from the lead engine) should 

make it somewhat easier for locomotive engineers to control in-train forces. Running counter to 

 

16This may indicate misuse of the code or simply that the derailment occurred as the train was departing or 

arriving a yard location.
14 

this influence, however, is the more extensive use of pre-blocking of cars to destination and the 

trend toward heavier-tonnage trains. 

 Over the long term, the development of Electronically Controlled Pneumatic (ECP) 

braking, with its more even brake applications and graduated brake release, offers promise for 

better management of in-train forces (at least buff forces). However, despite the apparent 

readiness of the technology, and despite successful demonstration of ECP train brakes, there is 

presently no established timetable or implementation plan for applying ECP brakes to either the 

existing fleet or new fleet segments. FRA has awarded a contract for an 18-month study into the 

costs and potential benefits of ECP brakes, with the hope of identifying a plausible migration 

path to ECP brakes and encouraging industry action. 
15 

In-Train Placement of Hazardous Materials Cars

urrent in-train placement rules generally require a "six-deep" separation between a 

hazardous materials carrying tank car and a locomotive or occupied caboose. These rules 

grew out of "good practices" established at a time when railroads used steam locomotives that 

produced hot cinders and carried freight, including explosives, in wooden box cars. Some 

separation between hazardous materials cars and the parts of trains occupied by humans is 

intuitively correct, but research by FRA and others points out that the risk of incompatible 

chemicals mixing in a derailment is small and must be balanced against the risk of crew injuries 

during any extra switching required by stringent car placement rules. 

Regulations: Just after the turn of the 20th century, Congress directed the Interstate 

Commerce Commission to formulate and publish "Regulations For The Transportation Of 

Explosives" to promote the safe transportation in interstate commerce of explosives and other 

dangerous articles. As the only nation-wide transportation system, the railroads played a large 

role in the early framing of the rules and created the Bureau for the Safe Transportation of 

Explosives and Other Dangerous Articles (later called the Bureau of Explosives) within the AAR 

to inspect shipments and methods of manufacture and packing. 

 

 Impetus for the early laws and regulations was provided by a number of accidents 

relating to shipments of black powder. It is thus not surprising that the first train placement rules 

dealt with cars containing explosives. These early regulations required cars of explosives to be 

placed near the center of the train, and at least 16 cars from the engine and 10 cars from the 

caboose, when the length of train would permit. The "16 deep" rule was chosen because it was 

considered to be a "safe distance" during a time when railroads used steam locomotives that 

produced hot cinders and carried freight, including explosives, in wooden box cars. 

 By 1922, regulations were in effect to require cars placarded INFLAMMABLE17 to be 

placed in trains at least five cars from the engine and five cars from the caboose. When the 

length of the train did not permit this placement, the hazardous materials car was to be placed 

near the middle of the train, separated from the engine or an occupied caboose by at least one 

car, and the engine crew was to be informed of its presence and location in the train. Under no 

circumstances could an INFLAMMABLE car be placed next to a car transporting explosives. 

 

17 The term "INFLAMMABLE" was confused with "unflammable" or "non-flammable" and the class name was 

changed to FLAMMABLE.

C
16 

 The current in-train placement requirements18 are founded on no more rigorous a 

scientific basis than were the original. They are, rather, based on the empirical evidence of 

history and on a sense of what "ought" to be, driven by concerns for the safety of crew members. 

This is not intended as criticism. The current in-train placement and separation regulations seem 

to have served the cause of safety well, and no body of evidence has emerged from the analysis 

of accidents or incidents to suggest the need for sudden or drastic overhaul. 

 

Position in Train of Placarded Cars 

Transporting Hazardous Materials 

Placard 

Group 1 

Placard Group 2 Placard group 3 Placard 

RESTRICTIONS Group 4 

Rail Car Tank Car Rail Car Tank Car Rail Car Rail Car 

1. When train length permits, placarded car may 

not be nearer than the sixth car from the engine or 

occupied caboose. 

X X 

X 

 

2. When train length does not permit, placarded car 

must be placed near the middle of the train, but not 

nearer than the second car from an engine or 

occupied caboose. 

X X X 

3.An open-top car when any of the lading 

protrudes beyond the car ends or if shifted would 

protrude beyond the car ends. 

X X X 

4. Loaded flat car except closed TOFC/COFC 

equipment, auto carriers, and other speciallyequipped cars with tie-down devices for handling 

vehicles. Permanent bulk head flat cars are 

considered the same as open-top cars. 

X X X 

5. Any rail car, transport vehicle, or freight 

container with temperature control equipment or 

internal combustion engine in operation. 

X X X 

6. Placarded cars may not be placed next to each 

other based on the following: 

 Placard Group 1.................................................. 

 Placard Group 2.................................................. 

 Placard Group 3.................................................. 

 Placard Group 4.................................................. 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

 Placard Group: 

 Group 1: Divisions 1.1 and 1.2 (Class A explosive) materials. 

 Group 2: Division 1.3, 1.4, 1.5 (Class B and C explosive), Class 2 (compressed gas; other than Div 2.3, PG I, Zone A), Class 3 (flammable liquid), 

Class 4 (flammable solid), Class 5 (oxidizing), Class 6 (poisonous liquid; other than Div 6.1 PG I, Zone A), and Class 8 (corrosive) 

materials. 

 Group 3: Divisions 2.3 (PG I, Zone A; poisonous gas) and 6.1 (PG I, Zone A; poisonous liquid) materials. 

 Group 4: Class 7 (radioactive) materials. 

* Where an "X" appears at the intersection of a Placard Group column and a Restriction row, the corresponding restriction applies. 

 

18 The current regulations, at 49 CFR § 174.85, use a table to graphically display requirements that, until 

December 1990, were contained in §§ 174.85 through 174.93.
17 

 The regulations now specify a 6-deep / middle of the train / buffer car requirement. That 

is, loaded placarded cars (other than those placarded combustible) may not be placed nearer than 

the sixth car from the locomotive or occupied caboose, if the length of the train permits it. If 6 

deep is not possible, then loaded placarded cars must be placed in the middle of the train and 

separated from the locomotives or occupied caboose by at least one nonplacarded car. The 

regulations also require the segregation of certain cars from other cars. The chart, reproduced 

above from § 174.85, provides the details. 

 In some limited cases, hazardous materials transportation has been permitted without a 

"buffer" or "spacer" car. Unit trains transporting sulfuric acid are currently operating in 

Canada19 without buffer cars under specific regulatory endorsement. However, in the United 

States there are a very few nearly-unit trains of hazardous materials, and they operate with a 

buffer between the loaded placarded cars and the occupied locomotive and caboose. 

 Cabooseless train operations are now common and FRA is considering whether or not to 

require segregation of loaded placarded hazardous materials cars from the rear of such trains. 

At least part of the impetus for an amendment is a recommendation (R-87-17) to that effect from 

the National Transportation Safety Board. The purpose of the recommendation was to protect 

the engine crew on following trains from striking hazardous material cars that could be 

positioned on the rear-end of a leading train. 

Issues: In-train placement of hazardous materials presents at least three categories of 

issues: (1) employee versus public safety, (2) the potential for chemicals to mix with adverse 

reactions versus the proximity of chemical-laden cars to sources of ignition, and (3) train 

placement versus train make-up. The following section is a brief description of some of the 

dimensions of the issues, including a discussion of supporting research studies. 

 The safety of the public is enhanced when the number of accidents is reduced or when the 

consequences of any given accident are lessened. "Optimum" performance of a system for 

placing hazardous materials cars in trains, then, would be achieved when these cars were so 

marshaled (to use the Canadian term) that an accident to one would not affect another. For 

instance, if 10 cars of liquefied petroleum gas were scheduled to be moved in a 110-car train, 

 

19 Unit trains, so named because they move one commodity in a single train directly from shipper to consignee, 

have been successful in moving tremendous tonnages of grain and other agricultural products, lumber, and coal. 

More recently, beginning in 1967, a major Canadian producer of sulfuric acid has proven that unit trains can move 

large quantities of this basic industrial chemical safely. The hazardous materials regulatory body in Canada granted 

this unit train an exception; regulations in effect in both Canada and the United States at the time were nearly 

identical in requiring at least one buffer car.
18 

they could be inserted as every tenth car. This would separate each one from all others and would 

require the derailment of more than 10 cars before 2 such cars would become involved. 

However, this plan would require 10 times more switching than moving the cars as a solid block 

and, if any part of the train derailed, this plan would essentially guarantee that a liquefied 

petroleum gas car would be involved. 

 On the other hand, switching railroad cars involves the risk of accidents and employee 

injury. If the goal is a reduction in accidents and injuries during switching operations, railroad 

workers would be protected, and "optimum" performance would thus be achieved, when the cars 

are marshaled to reduce the number of switching movements. Because the whole system for 

moving hazardous materials safely by railroad has such a good safety record, FRA is reluctant to 

attempt to "improve" safety by issuing regulations that will markedly increase the switching 

movements for cars of hazardous materials. Switching also involves the risk of overspeed 

impact, and–historically–some of the most catastrophic rail accidents involving hazardous 

materials have been in classification yards, with effects into the adjacent or nearby 

neighborhoods. Accordingly, a tradeoff of more highly refined train placement requirements 

could be more numerous incidents involving release of hazardous materials. Maximum total 

safety is not achieved by asking one group of "at risk" people to accept more risk so that another 

group will endure less. Despite the controversy woven throughout this issue, there is, 

effectively, universal agreement that the hazardous materials in a train should be separated from 

the portions of the train carrying people. 

 A hazardous materials train derailment theoretically could create a "witches brew" of 

chemicals that react to produce reactions more volatile, and fumes more toxic, than any of the 

individual products. In-train placement regulations do consider both reducing the likelihood of a 

tank puncture -- by prohibiting a hazardous materials tank car next to a load of telephone poles, 

for instance -- and reducing the lethal effects of the post accident scene -- by requiring, for 

instance, that poison gas and explosives cars not be coupled to each other. 

Research: The Transportation Systems Center (now, 

the Volpe National Transportation Systems Center) published a 

study in March of 1979 exploring the idea that most 

derailments involve cars placed towards the front of a train.20

TSC's analysis grew from a determination of the in-train 

location of all derailed units in reportable accidents for the 

years 1975, 1976, and 1977. After eliminating what it called 

 

20 Fang, Paul Ching-I and Reed, H. David, "Strategic Positioning Of Railroad Cars To Reduce Their Risk Of 

Derailment," Internal Staff Study, Transportation Systems Center (DOT/TSC), March 1979.

30.1

38.7

29.6

36.2

23.5

25.1

16.8

Portion of Train

First Second Third Fourth

(Transportation Systems Center)

Position in Train of Derailed Cars
19 

"bad data," for instance, reports where the number of cars derailed equaled a greater number than 

the length of the train, TSC was left with over 22,000 derailments over the three-year period. 

 Dividing the train into thirds, TSC found that 38.7 percent of the cars derailed were in the 

first third of the train, 36.2 percent were in the middle third, and 25.1 percent were in the last 

third. Splitting the train into quarters showed 30.1 percent of the cars derailed were in the first 

quarter, 29.6 in the second, 23.5 in the third, and 16.8 in the last quarter of the train. The data 

also appear here as a bar graph. The study concluded that the risk of derailment is higher in the 

forward section of the train than in the rear third or rear quarter of the train. 

 Under contract with FRA, Battelle completed a more recent study.21 Because Battelle 

concentrated on identifying opportunities for reducing the number and severity of hazardous 

materials car derailments, it selected only derailments on "main track" involving "freight trains" 

and "mixed trains," and it eliminated any derailment 

associated with a "short train," that is, a train with 10 

or fewer cars and locomotives. As with TSC, Battelle 

weeded out "bad data" and developed a final total of 

5,451 derailments in 1982 through 1985.22 The threeand four-section analysis of derailments in this study 

is similar to the earlier TSC project, and appears in 

the accompanying bar graph. Both studies show that 

the risk of derailment is significantly less in the rear 

of the train. The Battelle study also shows that the 

next safest section of the train is the front and the four 

section analysis indicates that, except for the rear of 

the train, "...there is little difference in the relative 

safety of the first three quarters."23 

 

21 Thompson, R.E., Zamejc, E.R., and Ahlbeck, D.R., Hazardous Materials Car Placement In A Train Consist, 

Final Report, Technical Task No. 6, Contract No. DTFR53-86-C-00006, 1989. The study is in two volumes: 

Volume I, Review and Analysis, and Volume II, Appendices.

22 An analysis by Battelle, within its report, demonstrates that mainline, long-train derailments constitute 

approximately the same percentage of incidents during the years included in the TSC study as in the years examined 

by Battelle. The more recent study simply focuses on a subset of the overall statistics. 

23 Battelle study, Vol. I, p. 11. Battelle attributes the relatively minor statistical differences between its study 

and the TSC work to the examination by TSC of derailments on all types of track, rather than on mainline track 

only. Battelle also excluded "short" trains and this may well have given a clearer picture of the relationship between 

each of the thirds or quarters of the train. (The average length in Battelle's study was 81 cars and locomotives. In 

the VNTSC work, it was 65.) 

24.6

33.6

28.2

37.9

27.6

28.5

19.6

Portion of Train

First Second Third Fourth

(Battelle Memorial Institute)

Position in Train of Derailed Cars
20 

 If mainline track operations were all that needed to be considered and, if avoiding 

derailments were the overwhelming priority, a hazardous materials placement strategy 

concentrating on the rear portion of the train would seem wise. However, train marshaling is 

not that simple. Another FRA study24 concluded that the preferred location for loaded cars is 

towards the front of the train because, under braking, heavy cars decelerate more slowly than 

empty cars and, if placed towards the rear, would "push" the more rapidly decelerating empty 

cars in front of them and generate high buff forces. Another danger of placing extended strings 

of light cars ahead of loads is the "stringline" effect.25 Analysis of the July 14, 1991 accident at 

Dunsmuir, California,26 shows that the pulling force of the engines combined with the drag of 

heavy loads may cause a group of light cars (especially long, light cars) to be pulled off the 

tracks and towards the inside of a curve. The tighter the curve, the more pronounced the possible 

effect. 

 Yet another set of complications arises in the consideration of hazardous materials 

incompatibility. Battelle reviewed the top 100 hazardous materials transported by rail, ranked 

by number of tank car shipments.27 Each commodity on the list was paired with every other and 

the pairs were considered "incompatible" if the combination produced greater lethal effects than 

either of the individual components. The research chemists evaluating the commodity pairs 

regarded the following effects as particularly dangerous: 

! Toxic chemical releases, 

! Fireballs, 

! Unconfined vapor cloud explosions, 

 

24 Nayak, P.R. and Palmer, D.W., "Issues and Dimensions of Freight Car Size: A Compendium," Report No. 

FRA/ORD-79/56, January 1980.

25 “Stringlining” was discussed earlier in this report.

26 An earlier example is the November 9, 1977, accident at Pensacola, Florida where a derailment, at least partly 

attributable to the "stringline" effect, lead the puncture of a tank car of anhydrous ammonia and the resulting gas 

cloud caused 2 deaths, many injuries, and the evacuation of 1,000 people. 

27 A list is published each year by the Bureau of Explosives of the Association of American Railroads. The 

Battelle study used the 1986 list; the most recent list available is in Annual Report of Hazardous Materials 

Transported by Rail, Year 1995, Report BOE 95-1, Bureau of Explosives, Association of American Railroads, 

Washington, D.C., September 30, 1995. From year to year, the rankings of the commodities are remarkably 

consistent. The report uses data garnered from the second generation of the AAR's TeleRail Automated Information 

Network (TRAIN II), the industry's rail car interchange data base. 
21 

! Condensed phase explosions, or 

! Pool fires - thermal radiation hazards, toxic combustion products. 

 Battelle ranked the pairs of chemicals on the basis of both their potential consequences 

and their risk. Chemical mixtures with the worst consequences include: 

! Oleum with organic chemicals: Can produce toxic emissions, fire balls, and 

unconfined vapor cloud explosions; 

! Fuming nitric acid with organic chemicals: Can yield toxic emissions, fire balls, 

and unconfined vapor cloud explosions; 

! Hydrogen peroxide with organic chemicals: Can give off toxic emissions and 

undergo condensed-phase explosions; 

! Sodium metal with commodities containing water: May result in fire ball or 

unconfined vapor cloud explosion; and 

! ASTM Group 1 (Nonoxidizing mineral acids) with ASTM Group 2 (oxidizing 

mineral acids): Toxic emission consequences. 

Consequence-based ranking yielded an interesting sidelight; according to the report, 

 It is interesting to note that mixing of chemicals will generally mitigate the 

toxic emission consequences of highly toxic chemicals such as hydrocyanic acid, 

chlorine, anhydrous ammonia, and hydrogen fluoride. An exception is the 

combination of hydrocyanic acid with chlorine, which may form cyanogen 

chloride, a tear gas. In the case of hydrogen fluoride, all combinations resulted in 

either the same or reduced consequences as compared with the unmixed 

chemicals. 

 Similarly, mixing will generally mitigate the consequences (fireballs and 

UVCE's) of highly flammable chemicals including hydrocyanic acid, 

acetaldehyde, and ethylene oxide.28

This serendipitous mitigation of the consequences of chemical releases is especially interesting 

in a "real world" transportation situation, where safety and risk decisions are interlaced with 

economic and traffic-flow decisions and where the overall safety of rail borne hazardous 

materials transportation is already very good. 

 

 

28 Battelle study, p. 76.
22 

 When calculating the risk-based rankings, Battelle combined the consequences of mixing 

an incompatible chemical pair with the yearly number of tank car movements of the 

commodities. The reasoning was that the volume of movements gives an indication of the 

potential frequency for the chemicals to be involved in the same derailment; this reasoning is 

admittedly imperfect because it does not allow for different patterns of distribution for various 

chemicals or for seasonal patterns in their transportation volumes.29 

 Normalized risk was established by dividing the risk of each pair by the risk of the lowest 

contributor in the pair.30 Of the commodity pairs in the study, the lowest combination was 

hydriodic acid and acrylic acid, and this was assigned a normalized risk equal to one. All other 

combinations were ranked relative to how much greater their risk was than the lowest. The 

combination of hydrochloric acid with sulfuric acid has the greatest risk, and it is over five times 

the risk of hydriodic acid with acrylic acid. According to the Bureau of Explosive's annual 

report of hazardous materials transportation, over 70,000 tank cars of sulfuric and hydrochloric 

acids moved in 1992, compared with fewer than 4,000 for the pair with the lowest risk ranking. 

The Battelle report attributes more than 50 percent of the risk to the following combinations: 

! Oleum with sodium hydroxide, methyl alcohol, denatured alcohol, or fuel oil; 

! Sulfuric acid with hydrochloric acid, methyl alcohol, denatured alcohol, vinyl 

chloride, hydrofluorosilicic acid, carbon tetrachloride, or benzene; 

! Sodium hydroxide with styrene, acetic acid, or carbon tetrachloride; and 

! Chlorine with anhydrous ammonia or hydrocyanic acid. 

 Based on its findings thus far, Battelle went on to consider car-to-car separation within a 

train. "The minimum segregation distance," according to the report, "is the spacing distance 

between HAZMAT rail tank cars which is required to prevent mixing of incompatible chemicals 

during train accidents involving derailments."31 The distance cannot be defined precisely 

because of the varying effects of terrain, natural and constructed drainage systems, and the 

surface adsorption of liquids. Individual hazardous materials spills can also be affected by the 

weather at the time of the accident. Recognizing these limitations, Battelle concludes that a 

 

29 As just two examples, anhydrous ammonia, an important agricultural fertilizer, moves most heavily during 

the growing season and the largest volumes of liquefied petroleum gas move during the heating season for homes 

and industries. 

30 "Risk," for these purposes, is a concept developed by combining the consequences of a particular chemical 

and the surface area over which those consequences are likely to be felt. A more complete discourse is given in the 

Battelle study.

31 Battelle report, p. 78.
23 

complete spill of a 100-ton tank car onto flat, "normally" adsorptive soil would affect a roughly 

circular area with a radius of about 40 meters ("132 feet). 

 During derailments, tank cars often turn at right angles to the track and stack up - not 

unlike a stack of firewood.32 The September 28, 1982, derailment on the Illinois Central Gulf 

Railroad at Livingston, Louisiana,33 is considered by the Battelle study as a "worst case" 

example. In that accident, 42 railroad cars, nearly all of them tank cars loaded with hazardous 

materials, derailed and most of them lost all or part of their contents. The tank cars stacked up so 

severely that 30 were compressed into an area about 265 feet long, or only about 5 car lengths. 

A spill from the first car in the stack could, assuming Battelle's 40-meter affected area, have 

mixed with a spill from the 30th car. If the spill from each car affected a 40-meter circle, then 

the separation distance after a derailment would have to be 80 meters, and to accomplish that at 

Livingston would have required a separation distance of 30 cars. 

 Because the Livingston derailment is considered a worst case, the study determined the 

average maximum number of derailed cars is 13 and concluded that a 15-car separation would 

provide the 40-meter post-derailment clear zone to minimize commingling of incompatible 

chemicals. 

 Canadian authorities have also evaluated risks to train crews and the general public 

associated with position and separation distances of hazardous materials in a train. A March 

1991 research study reported an investigation made by the Institute of Guided Ground 

Transport34 to determine: 

(1) extent to which regulatory restrictions governing the train placement of hazardous 

materials interfere with the recommended practices of train make-up for safe train 

handling; and 

(2) whether more compatible regulations involving train handling will improve the 

overall safety and efficiency of the movement of hazardous materials by railroad. 

 

32 These derailments are also called "accordion" derailments.

33 The National Transportation Safety Board report on the accident is number NTSB/RAR/83/05, "Derailment 

of Illinois Central Gulf Railroad Freight Train Extra 9629 East (GS-2-28) and Release of Hazardous Materials at 

Livingston, Louisiana, September 28, 1982."

34 English, G.W., Cattani, T.K., and Schweir, C., "Assessment of Dangerous Goods Regulations in Railway 

Train Marshalling," a working paper prepared for Transport Canada by the Canadian Institute of Guided Ground 

Transport, Queen's University at Kingston, Ontario, March 1991.
24 

As noted, the Canadian regulations are similar to those promulgated by RSPA. The most notable 

exceptions deal with unit trains of placarded tank cars--no buffer cars are required--and with a 

five-car separation requirement between cars carrying Division 2.1 (flammable gases) and loaded 

tank cars transporting chlorine, anhydrous ammonia, or sulfur dioxide.35 

 Neither of the major Canadian railroads has had an incident where hazardous materials 

placement specifically contributed to a train handling derailment. Canadian National Railways, 

with relatively flat and straight routes, pointed out that, while a concentration of heavy cars at the 

rear of the train might be troublesome, a concentration of empty cars there is not necessarily 

preferred, and might cause more problems than randomly distributed empty cars. The Canadian 

study also noted that the separation requirements for hazardous materials cars required extra 

switching moves and a consequent increased exposure to accidents or injuries when performing 

them. 

 The Canadian Institute of Guided Ground Transport (Institute) took a long look at the 

segregation analysis made by Battelle and noted that the risk rankings there do not consider the 

frequency at which commingling might be expected to occur. Some idea of the frequency of a 

specific hazardous material being involved in a specific derailment, sometimes known as the 

exposure risk, can be gathered using the following steps: 

Divide the hazardous materials carloads by the total carloads, multiply that result by the 

average ratio of loaded car moves to total car moves, then multiply by the probability of 

release upon derailing, and then multiply by the average number of cars derailing in a 

derailment. 

 Making the calculations, the Institute determined that the probability of two common 

acids both being present and both releasing is on the order of 5.5 X 10-8 or about 55 chances per 

billion derailments. Performing the same calculations on Battelle's highest risk pair, 

hydrochloric acid and sulfuric acid, creates a combined probability 2,643 times smaller than the 

individual probabilities. The Institute also notes that these rough assessments have not 

considered the probability of effective mixing of the two commodities, nor the probability that 

the derailment would happen anywhere near a populated area. 

 

35 The major railways operating in Canada have argued that this requirement to separate Division 2.1 from the 

other named gases is a knee-jerk reaction to a massive derailment and fire at Mississauga, Ontario, (near Toronto) in 

which the presence of a tank car of chlorine in the midst of a conflagration of liquefied petroleum gas cars led to an 

evacuation of nearly 500,000 people. It was later determined that the chlorine car had indeed been breached and 

most of its contents had escaped in the thermal plume. 
25 

 Using actual traffic patterns through an area of suburban Toronto and using any 

"oxidizing or poisonous substance" combined with any other hazardous materials shipment, the 

Canadian study calculated that the chances of a derailment with a combined release are between 

0.0042 per million and 0.0017 per million derailments. 

 Finally, the Canadian study noted that many of the worst consequence combinations 

carry the same placard (hydrochloric acid and sulfuric acid are both in Class 8, formerly 

corrosive materials) and current regulations in either Canada or the United States do not require 

buffer cars between commodities of the same class. By contrast, the Canadian restriction of fivecar separation between Flammable Gases (Class 2.1) and chlorine, anhydrous ammonia, and 

sulfur dioxide is enforced on commodities not considered incompatible (in that the combination 

was not more lethal than either individual chemical), while chlorine and anhydrous ammonia 

themselves were not required to be separated even though they are considered to present an 

explosion hazard. 

 

 The Institute study mentions a British Railways study36 performed by Bowring Protection 

Consultants. The purpose of the British study was to identify the risks associated with the 

existing segregation requirements for dangerous goods and to explore the possibility of either 

relaxing or strengthening them. In some instances the British regulations are less restrictive than 

those of Canada and the United States. For instance, no buffer car is required between occupied 

rail cars and cars transporting hazardous materials. British regulations, however, tend to be more 

restrictive in the area of compatibility requirements. For example, there are more combinations, 

which require single car buffers and, under some conditions, hazardous materials cannot be 

transported in the same train regardless of separation. The study concluded that the probability of 

dangerous combinations happening on British Rail is low enough under a random marshaling 

strategy that it is not an immediate cause for concern. 

 

 

36 Considine, M., A Risk Based Approach to the Segregation of Dangerous Goods on the Railways, Bowring 

Protection Consultants, prepared for British Railways Board, Contract No. RE21090, March 1988. The Canadian 

Institute notes that this is a confidential report and it was furnished by Transport Canada. FRA has not read and 

evaluated the report text itself. The comments included here are those of the Canadian Institute of Guided Ground 

Transport. 
26 

Conclusion

ach year, railroad switchmen are injured, equipment is damaged, and hazardous materials 

are released in switching accidents, and at least some of that switching happens in order to 

satisfy the requirements for positioning placarded rail cars in trains. "In-train placement" 

involves issues of separating hazardous materials cars from parts of the train occupied by people 

and segregating hazardous materials cars, one from the other; it differs from train make-up, 

where the goal is to place cars into a train such that they balance the forces within the train. 

 The issue of train make-up to control improper weight distribution and the consequent 

imbalance of forces within the train present complex technical problems that have been the 

subject of extensive research supported by FRA and the industry over two decades. The railroad 

industry has used the products of FRA's research to develop and implement guidelines for train 

make-up, and FRA intervenes to encourage more conservative train make-up practices where the 

need to do so is apparent. Development of more formal Federal policies or requirements has 

been delayed by the unavailability for independent analysis of an appropriate train dynamics 

simulator. However, a new modeling tool is currently under development through FRA’s Office 

of Research and Development, and when it is available in a validated form it should permit FRA 

to more closely evaluate the industry’s performance in maintaining appropriate train make-up. 

 Existing regulations regarding train placement of hazardous materials cars have been 

fashioned through long experience and have functioned well. The requirement that tank cars 

carrying hazardous materials be place at least six deep provides suitable protection for train 

crews without creating excessive issues regarding train make-up (e.g., location of loaded cars). 

Use of a buffer car at the back of each train containing hazardous materials may have some merit 

to reduce the consequences of rear end collisions, but thus far the use of cabooseless trains 

(which itself reduces risk to crew members who would have been riding the relatively fragile 

caboose) has not resulted in significant additional exposure to head-end crews; and, as discussed 

in this report, additional switching results in safety as well as economic costs. Risk analysis 

regarding product combinations has not indicated any compelling need to alter existing 

requirements that provide for separation of certain commodities to limit, insofar as is practical, 

undesirable interactions should the train derail. Accordingly, existing in-train placement 

requirements appear to provide for an appropriate level of safety. 

E