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The fact that some incidents included in the CPUC data- to the NTD on a monthly basis. The NTD relies entirely on
base were not found in the local transit agency databases raises incident data submitted by local transit agencies; unlike the
the question of how they were obtained by the SSO agency. SSO agencies, the NTD is incapable of conducting indepen-
One reason CPUC has a higher rate of reported accidents may dent investigations of transit incidents.
be that CPUC has a designated representative for each transit Table 26 shows the number of incidents recorded for
agency that has a close working relationship with the local safety each local transit agency in the NTD database compared to
manager and usually participates with the transit agency in acci- the number of incidents recorded in the local transit agency
dent investigations. Depending on the severity, the CPUC may databases.
perform its own independent investigation. Besides engineers Table 26 shows that in total, the size of the NTD database
on the staff, CPUC also has FRA certified railroad inspectors, was approximately half the size of the local agency data-
i.e., signal and train control, motor power and equipment, and bases over the same period of time. However, there was
track inspectors to conduct independent investigations. All substantial variation observed in the relative number of
incident reports originate from the transit agency, and are incident records in the transit agency databases compared
reported as required by FTA rules. It is also possible that the to the NTD database. For example, when the SEPTA records
datasets provided by the three local transit agencies simply did were removed, the total number of records in the NTD data-
not contain all of the records for the years examined. base was one-quarter the number in the remaining local
Whatever the explanation for the differences found, the transit agency databases.
fact that each organization maintains their own database Table 27 shows the proportion of incident records in the
independent of each other is surely a significant contributor local transit agency databases also found in the NTD database.
to the apparent discrepancy and the uncertainty that may Table 27 shows that, in total, almost 40% of the incident
arise in subsequent analysis. It is clearly important to have records contained in the local agency databases were also con-
confidence that a dataset is complete in order to carry out sta- tained in the NTD database. However, this statistic was cut in
tistical examinations. half with the removal of the SEPTA database from the cal-
culation. This difference may have been partially due to the
severity of the incidents experienced on different transit sys-
Comparison of Local Transit Agency
tems. Some agencies may have experienced a high number of
and NTD Databases
total collisions with relatively few meeting the NTD criteria.
Local transit agencies are obligated to report incidents meet- However, it is more likely that this difference reflects variation
ing the criteria specified in the Data Collected by NTD section in collision reporting practice, either in what incidents local
Table 26. Number of records in NTD database compared to local transit
agencies.
Number of
Size of NTD
Incidents Number of
Relative to the
Reported in Incidents
Agency Name Size of Local Years
Local Reported in
Agency
Agency NTD Database
Database
Database
Los Angeles County
Metropolitan Transportation
Authority 175 111 63.4% 20022006
Minneapolis Metro Transit 22 19 86.4% 20042007
New Jersey Transit Corporation 50 1 2.0% 20022007
San Francisco Municipal
Railway 387 62 16.0% 20062007
Santa Clara Valley
Transportation Authority 153 15 9.8% 20022007
Southeastern Pennsylvania
Transportation Authority 1335 954 71.5% 20022005
Tri-County Metropolitan
Transportation District of
Oregon 253 72 28.5% 20022007
Grand Total 2375 1234 52.0%
Total (without SEPTA) 1040 280 26.9%
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Table 27. Local transit agency data transferred to the NTD.
Agency Name Number of Number of % of Agency- Years
Incidents Local Agency Level
Reported in Incidents Also Incidents Also
Local Agency Reported in Reported in
Database NTD Database NTD Database
Los Angeles County
Metropolitan Transportation
Authority 175 95 54.3% 20022006
Minneapolis Metro Transit 22 9 40.9% 20042007
New Jersey Transit Corporation 50 0 0.0% 20022007
San Francisco Municipal
Railway 387 36 9.3% 20062007
Santa Clara Valley
Transportation Authority 153 9 5.9% 20022007
Southeastern Pennsylvania
Transportation Authority 1335 726 54.4% 20022005
Tri-County Metropolitan
Transportation District of
Oregon 253 65 25.7% 20022007
Grand Total 2375 940 39.6%
Total (without SEPTA) 1040 214 20.6%
transit agencies were willing to investigate, or in what inci- Approximately 76% of the records contained in the NTD
dents local transit agencies chose to report to the NTD. This database were also identified in one of the local transit agency
variation may have been the result of transit agencies failing to databases. As expected, this statistic revealed the reliance of
report incidents that satisfied the NTD reporting criteria, or the NTD on the incident records contained in the local agency
reporting incidents which did not meet these criteria. databases, but it is difficult to identify the origin of the remain-
Table 28 shows the proportion of NTD incident records ing records. The NTD does not conduct independent inves-
that also appeared in the local agency database. tigations of transit incidents, and relies entirely on the reports
Table 28. Proportion of NTD data records appearing in local transit
agency data.
Number of Number of % of Agency-
Incidents Incidents Also Level
Agency Name Reported in Reported in Incidents Also Years
NTD Database Local Agency Reported in
for Agency Database NTD database
Los Angeles County
Metropolitan Transportation 111 95 85.6%
Authority 20022006
Minneapolis Metro Transit 19 9 47.4% 20042007
New Jersey Transit Corporation 1 0 0.0% 20022007
San Francisco Municipal
62 36 58.1%
Railway 20062007
Santa Clara Valley
15 9 60.0%
Transportation Authority 20022007
Southeastern Pennsylvania
954 726 76.1%
Transportation Authority 20022005
Tri-County Metropolitan
Transportation District of 72 65 90.3%
Oregon 20022007
Grand Total 1234 940 76.2%
Total (without SEPTA) 280 214 76.4%
