My current impressions about the possible causes of the
The two collapsed spans of the roadway look CUT OUT, longitudinally and cross-sectionally, possibly in advance or shortly before the accident and as the preparation for it, possibly from the central, Crimea-outbound part of the highway. The third cross-sectional and partially longitudinal CUTS were probably made to limit the human casualties by stopping the traffic.
The cuts appear to be very accurate, “surgical”.
There might have been more than one truck involved, possibly several, possibly equipped with the specially designed and placed lasers or other types of the “cutting” devices.
The role of the “plastic bombs” implied by the FSB is unclear. Any bomb would produce the radially spreading damage with a lot of debris, which we do not see here.
The ignition of the fuel cisterns on the railroad above could be caused by the mechanism separate from those inducing the “cuts’ on the roadway, and these two events were carefully timed to coincide with the sliding of its two sections, possibly assisted by the kinetic effect of the shockwave from the railroad blast.