The cables are laid in a trench about 30 CM deep just off the curb the trench itself is maybe only 10 CM wide you have a single machine that digs the trench lays the coax and then covers it with gravel (which is made from the asphalt, dirt and gravel it digs up) after that they just put the asphalt over it and it's done they you can do 100-200M an hour or even more like this pretty easily.
If you need to redo the road you don't have to scrape off the trench part anyhow no car can drive so close to the curb, and even if you do scrape that part off it's just like scraping the road you usually only go maybe 1cm/half and inch deep you don't remove the entire surface and even if you need to redo the road completely you can leave the 10cm wide trench alone.
Also fiber and coax cables can last for decades there is no need to redo them, the same cables can be used again and again with each upgrade to the standard since to get more speed you only need to change the optical or RF equipment there is no need to change the cable.
The same cables that used to deliver 100mbit can be used for 10gbit and even higher speeds, multiplexing is also possible over older cables.
One thing i wondered it why simply they just don't make curb stones (e.g. http://image.made-in-china.com/2f0j00AeqanjdwtkoK/Blue-Stone...) with a few ducts in them already couple inches in diamiter so you could just pull fibers through at any time without having to even dig up the road... Yes you have to replace them, but how often do you that? every 10 years? 20 years? and if you design it well you can either pull the cable out or heck even replace the cable with the curb stone, people can live without internet for 6 hours during the night.