*Corresponding author:Myung cheol Park, Traffic Accident Analysis Division, National Forensic Service, Republic of Korea
How to cite this article:Myung Cheol P, Jong Hyuk K, Won Taek O, Sang Hyun L. A Method of Estimating the Distance and Relative Speed of an Object
when a Vehicle Hits It, as Indicated in the Black Box Image Created at the Moment of Impact. J Forensic Sci & Criminal Inves. 2020; 13(5): 555873. DOI: 10.19080/JFSCI.2020.13.555873.
This paper proposes a method by which the distance and relative speed of a vehicle vis-à-vis the object it hit are measured using the phenomenon in which when a vehicle impacts another vehicle, a pedestrian, or another object, if the object is n times distant from the black box, its image looks about n times smaller
Keywords:Forensic video; Car black box; Vehicle speed; Pixel; Distance; Relative speed; Impact; Collision
Method of measuring the object filmed by the vehicle’s black box
Figure 1 shows the method of measuring the distance of a tree filmed by a black box. The tree with 3 length was expected to be located 30 from the black box The aforementioned can be attributed to the fact that resembles , and as such, DODEAOAB=resembles ÄDOFand ÄAOCThus,//DOAOFOCO=. Therefore, //DEABFOCO=, so3//10hhFOm=, and FO is 30m. Figure 2 shows the method of measuring the distance of a stick filmed by the black box. At ()0ttt=−Δtime, the reference stick was moved so that its distance from the black box could be assumed as00dns=, and the reference stick was extended so that its extended length could be assumed as0hhnh=, with the top and bottom of the imaginary stick touching the imaginary lines. Then, 000hdnsns=and 0hhnh= 00hdsh∴ was expected. In the above expression, can be attributed to the fact that the black box image magnification may vary according to the distance, and to the possibility of magnification may vary according to the distance, and to the possibility of distortion [1-4]. In addition, it was assumed that after the black box image was captured at , the pixel of 0h would be 0p. Next, it was assumed that the pixel of captured from the black box image at was , and that the pixel of 0h was p, and 0pnp=.
Then, 00hdsh, 00phhp, and 0pnp=.
The distance d of the reference stick moved from the black box was estimated using the expression below.
Method of Measuring the Distance and Relative speed of a Pedestrian and the Vehicle ahead Filmed by the Black Box
Figure 3 & 4 shows the method of measuring the distance and relative speed of a pedestrian filmed by the black box. If the pedestrian’s distance from the black box is and the distance between the vehicle and the pedestrian is , then 0sds=−. Therefore, the distance is expected [5-9].
Further, if, at , the relative speed of the vehicle and the pedestrian is , is expected in the expression below
This study proposed the following [10-14]. If, at the time
when a vehicle hits an object, the horizontal distance from the
vehicle black box to the part of the object that was hit is assumed
as reference distance ; the pixel length of the part of the object
that was hit is assumed as ; and at the time of rewinding the
black box, the part of the object that was hit is assumed as , the
and correction factor are proposed for
measuring the distance from the vehicle to the object, and
and correction factor for measuring the
relative speed of the vehicle and the object are proposed. In
the experiment in this study, while the Hyundai Veracruz SUV
was travelling, its installed black box filmed the dummy. Then
the Veracruz black box filmed the rear side of the Sonata when
it faced the front, when it turned, and when the Sonata offset it.
Then the proposed method measured the distance from the black
box images. The image distortion correction factor was applied to
. ªThis confirmed a greater accuracy
in distance. Thus, the correction factor for correcting the two
said situations was applied to the expression
and this confirmed a greater accuracy in speed. In the experiment,
the four black boxes filmed various impact experiments, and
in the consequent impact images, the correction factor of 1.1
was unilaterally applied to the expression
. As such, the vehicle’s pedestrian impact speed average error
was determined to be 4.1%, and the maximum error, 3.1 km/h
(7.9%), at about 40 km/h. The vehicle’s vehicle impact speed
average error was measured as 3.1%, and the maximum error
was measured as 2.1 km/h (5.3%), at about 40 km/h. This
confirmed that the measured speed error was not big. Therefore,
in this study, in the general case of a sedan hitting another sedan,
a universal correction factor 1.1 was estimated. In this study,
and correction factor for the
measurement of the relative velocity between the vehicle and the
object. In order to reduce the error that occurs in a remarkably
complicated situation, only the correction factor is introduced.
However, many experiments have confirmed that the error is not
large. This equation is very simple and can be used conveniently
in actual situations. Thus, this study confirmed that the proposed
method can estimate the distance from a vehicle to the object it hit
in a traffic accident, and the relative speed of the object compared
to that of the vehicle that hit it, using the images created by the
vehicle’s black box. In addition, this method is expected to be
further verified and supplemented by widespread use in actual
traffic accidents. For this method, the relative speed estimation
will be further studied in cases where the black box is rotated and
the vehicle is offset. The method will be used in the development
of programs that are specially designed to calculate the relative
speed in real time.