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While some of these indications are easily applied, others present greater difficulties. In particular, the indication of
keeping in any situation the metric tape leaning against the
road surface is in some cases complicated if not completely
impractical.
There are two classic cases that can be taken as an example. In the first case, the central point of a bloodstain should
be measured; if, as indicated in the manuals, the metric tape
must be placed on the road surface, it will inevitably come
into contact with blood. While it is true that it is possible to
clean the metric tape without any particular problems after
the measurements, putting in contact a foreign object with
biological material violates one of the principles of investigative activity, namely that of avoiding contamination of
evidence.
In the second case, which is very frequent in urban environments with high density of population and vehicular
presence, it is not possible to keep the metric tape leaned well
adherent to the ground due to the presence of obstacles. In
some scenarios the problem can be overcome by tying the cornerstones not directly to the points to be measured, using a
greater number of projections; however, each new projection,
by increasing the measurements needed to bind the point to be
measured to the cornerstones, increases the margin of error of
the measurements.

Conclusions
The data (in this case the values of the measurements) that
relate to the physical evidence are subject to the possible weakness of the so-called " transmission chain, " which is the path
they take from the moment they are collected to the moment
they are entered into a system that must process them with
a high degree of reliability to extract quality information. As
demonstrated, the weak link in this chain is the one that links
data collected in a context in which it is impossible to fully
meet the criteria of uncertainty, calibration and traceability,
typical of metrology, to a context (that of the use of the material collected for the mathematical reconstruction of dynamics)
that instead assumes that, if the data are not completely accurate, at least we know how much their inaccuracy amounts.
This phase shift, at the state of the art, cannot be completely
eliminated, and can only be re-examined through the professionalism of the operators called to carry out the surveys.
Edoardo Riva has been a Member of the Milan City Police
Department since 1997 and currently holds the rank of Superintendent. He has more than twenty years of experience in the
fields of security, law enforcement and investigation. Edoardo
is a Crime Scene Investigation Expert and a Lecturer for Italian
and foreign universities on the subjects of forensics, security,
risk management and fraud investigation.

For Further Reading
" Best Practice Manual for Road Accident Reconstruction, " ENFSI, 2015. [Online]. Available: http://enfsi.eu/wp-content/uploads/2016/09/4._road_accident_reconstruction_0.pdf.
L.E. Martinez, " Traffic collision investigation manual for patrol officers, " Central Arizona Regional Law Officers Training Academy, 1994. [Online]. Available: https://www.tarorigin.com/art/Lmartinez/.
D. Topolšek, E. A. Herbaj, and M. Sternad, " The accuracy analysis of measurement tools for traffic accident investigation, " J. Transportation Technologies, vol. 4, pp. 84-92, 2014.
L. B. Fricke, Traffic Accident Reconstruction, Northwestern University Traffic Institute, 1990.

IEEE Instrumentation & Measurement Magazine

February 2021

http://enfsi.eu/wp-content/uploads/2016/09/4._road_accident_reconstruction_0.pdf http://enfsi.eu/wp-content/uploads/2016/09/4._road_accident_reconstruction_0.pdf https://www.tarorigin.com/art/Lmartinez/

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