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Shared-Track: Laying the Foundation--Policy and Strategy 25
Achieving Safety Equivalence
Equivalent safety is not expressly defined in 49 CFR 211, the legal basis for wavier petitions
and approved deviations from the Code of Federal Regulations (see Task 9, subsection "The
Waiver Process"). Federal law requires:
. . . the petition should explain how a level of safety at least equal to that afforded by the FRA rule will
be provided by the alternative measures the petitioner proposes . . . requires a quantitative risk analysis of
the risk of collision . . . (49 CFR 211, Appendix A, Section II, Part 2, Paragraph C).
In other parts of 49 CFR 211, the concept of equivalent safety is often cited. The lack of explicit
definition leaves this familiar and oft-quoted term open to interpretation both by regulators and
petitioners. The prospective operator should endeavor to satisfy federal regulators on a practi-
cal level by addressing several concerns as part of its waiver petition.
· How is equivalent safety measured or evaluated in this project?
· What is the appropriate and acceptable method for comparing the safety of a fully compliant
operation to the proposed shared-track project?
· Is the validity of the comparison limited or qualified in any way?
Comparing measures of safety equivalence with standards for other modes of transportation
merits incorporation in any analysis. This multi-modal risk analysis should consider the null
alternative (doing nothing), increased auto use, travel by bus, etc., that might result if a shared-
track system is not built. Such an approach has been used for proposed Mag-Lev systems and air
travel to determine overall risk, rather than mode specific risk.
Equal Risks, Equivalent Safety
Equivalent safety is best understood in terms of equal risks. Risk levels assumed for a federally
compliant system must remain unchanged for any operating alternatives proposed for the project.
Risk is defined as likelihood multiplied by consequence. Likelihood is the probability of a haz-
ardous condition arising. Consequence is the severity of the hazard. Likelihood itself is a com-
plex product of probability of a train encountering a hazardous event, number of trains and train
miles operated in a given time, and number of passengers on each train. Together likelihood and
consequence measure the total exposure of life and property to potential hazards. Table 4 pro-
vides a simple illustration of the three major constituents of total risk assessment.
Table 4. Illustration of three parts of total risk.
Likelihood
Probability Period Consequences
Definition Chance of a hazard event Units of transportation The average amount
affecting each unit of services operated in a of damage done given
transportation service. given time period. that a hazard event
occurs.
Aviation Chance of a plane crash on Number of flights Average number of
Example a given flight. operated per day. lives lost given a plane
crash.
Shared-Track Chance of an intrusion Number of light rail Average loss of life
Example accident affecting a light vehicle trips operated per and property given
rail vehicle and a freight day; number of freight that an intrusion event
train. trains operated per day. occurs.
Source of History of hazard events Operating plan and Accident history
Data provides a probability per ridership projection provides
unit of service. defines the units of quantification of
Assumptions are made transportation services to severity of each type
where there is insufficient be provided each day. of accident.
data.
