  Using the methods originally developed for Random Matrix Theory we derive an
exact mathematical formula for number variance (introduced in [4]) describing a
rigidity of particle ensembles with power-law repulsion. The resulting relation
is consequently compared with the relevant statistics of the single-vehicle
data measured on the Dutch freeway A9. The detected value of an inverse
temperature, which can be identified as a coefficient of a mental strain of car
drivers, is then discussed in detail with the respect to the traffic density
and flow.
