  The fundamental diagram for tunnel traffic is constructed based on the
empirical data collected during the last two years in the deep long branch of
the Lefortovo tunnel located on the 3$^\text{rd}$ circular highway of Moscow.
This tunnel of length 3 km is equipped with a dense system of stationary
radiodetetors distributed uniformly along it chequerwise at spacing of 60 m.
The data were averaged over 30 s. Each detector measures three characteristics
of the vehicle ensemble; the flow rate, the car velocity, and the occupancy for
three lanes individually. The conducted analysis reveals an original complex
structure of the fundamental diagram.
