Appendix D to Part 222 - Determining Risk Levels
49:4.1.1.1.17.5.15.1.28 : Appendix D
Appendix D to Part 222 - Determining Risk Levels Introduction
The Nationwide Significant Risk Threshold, the Crossing Corridor
Risk Index, and the Quiet Zone Risk Index are all measures of
collision risk at public highway-rail grade crossings that are
weighted by the severity of the associated casualties. Each
crossing can be assigned a risk index.
(a) The Nationwide Significant Risk Threshold represents
the average severity weighted collision risk for all public
highway-rail grade crossings equipped with lights and gates
nationwide where train horns are routinely sounded. FRA developed
this index to serve as a threshold of permissible risk for quiet
zones established under this rule.
(b) The Crossing Corridor Risk Index represents the
average severity weighted collision risk for all public
highway-rail grade crossings along a defined rail corridor.
(c) The Quiet Zone Risk Index represents the average
severity weighted collision risk for all public highway-rail grade
crossings that are part of a quiet zone.
The Prediction Formulas
(a) The Prediction Formulas were developed by DOT as a guide for
allocating scarce traffic safety budgets at the State level. They
allow users to rank candidate crossings for safety improvements by
collision probability. There are three formulas, one for each
warning device category:
1. automatic gates with flashing lights;
2. flashing lights with no gates; and
3. passive warning devices.
(b) The prediction formulas can be used to derive the following
for each crossing:
1. the predicted collisions (PC)
2. the probability of a fatal collision given that a collision
occurs (P(FC|C))
3. the probability of a casualty collision given that a
collision occurs (P(CC|C))
(c) The following factors are the determinants of the number of
predicted collisions per year:
1. average annual daily traffic
2. total number of trains per day
3. number of highway lanes
4. number of main tracks
5. maximum timetable train speed
6. whether the highway is paved or not
7. number of through trains per day during daylight hours
(d) The resulting basic prediction is improved in two ways. It
is enriched by the particular crossing's collision history for the
previous five years and it is calibrated by resetting normalizing
constants. The normalizing constants are reset so that the sum of
the predicted accidents in each warning device group (passive,
flashing lights, gates) for the top twenty percent most hazardous
crossings exactly equals the number of accidents which occurred in
a recent period for the top twenty percent of that group. This
adjustment factor allows the formulas to stay current with
collision trends. The calibration also corrects for errors such as
data entry errors. The final output is the predicted number of
collisions (PC).
(e) The severity formulas answer the question, “What is the
chance that a fatality (or casualty) will happen, given that a
collision has occurred?” The fatality formula calculates the
probability of a fatal collision given that a collision occurs
(i.e., the probability of a collision in which a fatality
occurs) P(FC|C). Similarly, the casualty formula calculates the
probability of a casualty collision given that a collision occurs
P(CC|C). As casualties consist of both fatalities and injuries, the
probability of a non-fatal injury collision is found by subtracting
the probability of a fatal collision from the probability of a
casualty collision. To convert the probability of a fatal or
casualty collision to the number of expected fatal or casualty
collisions, that probability is multiplied by the number of
predicted collisions (PC).
(f) For the prediction and severity index formulas, please see
the following DOT publications: Summary of the DOT Rail-Highway
Crossings Resource Allocation Procedure - Revised, June 1987,
and the Rail-Highway Crossing Resource Allocation Procedure:
User's Guide, Third Edition, August 1987. Both documents are in
the docket for this rulemaking and also available through the
National Technical Information Service located in Springfield,
Virginia 22161.
Risk Index
(a) The risk index is basically the predicted cost to society of
the casualties that are expected to result from the predicted
collisions at a crossing. It incorporates three outputs of the DOT
prediction formulas. The two components of a risk index are:
1. Predicted Cost of Fatalities = PC × P(FC|C) × (Average Number of
Fatalities Observed In Fatal Collisions) × $3 million 2. Predicted
Cost of Injuries = PC × (P(CC|C) - P(FC|C)) × (Average Number of
Injuries in Collisions Involving Injuries) × $1,167,000 PC,
P(CC|C), and P(FC|C) are direct outputs of the DOT prediction
formulas.
(b) The average number of fatalities observed in fatal
collisions and the average number of injuries in collisions
involving injuries are calculated by FRA as described in paragraphs
(c) through (e).
(c) FRA will match the highway-rail incident files for the past
five years against a data file containing the list of grade
crossings where the train horn was not routinely sounded over that
five-year period to identify two types of collisions involving
trains and motor vehicles: (1) Those that occurred at crossings
where the train horn was not routinely sounded during the period,
and (2) those that occurred at crossings equipped with automatic
gates where the train horn was routinely sounded. Certain records
will be excluded, including records pertaining to incidents where
the driver was not in the motor vehicle or where the motor vehicle
struck the train beyond the fourth locomotive or rail car that
entered the crossing. FRA believes that sounding the train horn
would not be very effective at preventing such incidents. 1
1 The data used to make these exclusions is contained in blocks
18 - Position of Car Unit in Train; 19 - Circumstance: Rail
Equipment Struck/Struck by Highway User; 28 - Number of Locomotive
Units; and 29 - Number of Cars on the current FRA Form 6180-57
Highway-Rail Grade Crossing Accident/Incident Report.
(d) Collisions in the group containing the gated crossings
nationwide where horns were routinely sounded will then be
identified as fatal, injury only or no casualty. Collisions will be
identified as fatal if one or more deaths occurred, regardless of
whether injuries were also sustained. Collisions will be identified
as injury only when injuries, but no fatalities, resulted.
(e) The collisions (incidents) will be summarized by year for
the five-year period preceding the year in which the risk index is
being updated. The fatality rate for each year will be calculated
by dividing the number of fatalities by the number of fatal
incidents. The injury rate will be calculated by dividing the
number of injuries in injury only incidents by the number of injury
only incidents. FRA will publish updated fatality and injury rates
on an annual basis in the Federal Register.
(f) Per guidance from DOT, $3 million is the value placed on
preventing a fatality. The Abbreviated Injury Scale (AIS) developed
by the Association for the Advancement of Automotive Medicine
categorizes injuries into six levels of severity. Each AIS level is
assigned a value of injury avoidance as a fraction of the value of
avoiding a fatality . FRA rates collisions that occur at train
speeds in excess of 25 mph as an AIS level 5 ($2,287,500) and
injuries that result from collisions involving trains traveling
under 25 mph as an AIS level 2 ($46,500). About half of grade
crossing collisions occur at speeds greater than 25 mph. Therefore,
FRA estimates that the value of preventing the average injury
resulting from a grade crossing collision is $1,167,000 (the
average of an AIS-5 injury and an AIS-2 injury).
(g) Notice that the quantity [PC*P(FC|C)] represents the
expected number of fatal collisions. Similarly,
{PC*[P(CC|C)-P(FC|C)]} represents the expected number of injury
collisions. These are then multiplied by their respective average
number of fatalities and injuries (from the table above) to develop
the number of expected casualties. The final parts of the
expressions attach the dollar values for these casualties.
(h) The Risk Index for a Crossing is the integer sum of the
Predicted Cost of Fatalities and the Predicted Cost of
Injuries.
Nationwide Significant Risk Threshold
The Nationwide Significant Risk Threshold is simply an average
of the risk indexes for all of the gated public crossings
nationwide where train horns are routinely sounded. This value will
be recalculated annually and published in a notice in the Federal
Register. For the most recent value of the Nationwide Significant
Risk Threshold, please visit FRA's public Web site at
http://www.fra.dot.gov.
Crossing Corridor Risk Index
The Crossing Corridor Risk Index is the average of the risk
indexes of all the public crossings in a defined rail corridor.
Quiet Zone Risk Index
The Quiet Zone Risk Index is the average of the risk indexes of
all the public crossings in a Quiet Zone. It takes into
consideration the absence of the horn sound and any safety measures
that may have been installed.
[71 FR 47634, Aug. 17, 2006, as amended at 72 FR 44792, Aug. 9,
2007]