Populate an empty field in a road network

Hi,
This is what I would like to achieve:

Say I have a polygon layer that includes three cities 'X', 'Y', & 'Z' (in reality I have more than 1000s). I also have a road network layer. I want to populate an empty field in the road network with corresponding city names. The city names will be extracted from the name field in the city polygon layer. That is the code block will first check which city boundary it falls in the populate the empty field with the corresponding city names.

any tips will be appreciated.
cheers
Kazi