Tunnelling - Engineering

Q1:

A tunnel is found more advantageous as compared to the alternate routes because it:

A remains free from snow

B reduces the cost by reducing the route distance

C reduces the maintenance cost

D avoids interference with surface rights

E All the above.

ANS:E - All the above.

How can it be possible that in the tumbling phenomenon the particles don't interfere? How can we prove that? Please explain.