What tech reduces the energy cost of roads?
There is a technology that reduces the upkeep cost of roads and Magrail, but I can't remember what it is, nor can I find it by searching the civopedia.
It's not a tech, it's an affinity, supremancy 3 actually
The level three affinity bonus for supremacy is one of the most useful: pay no maintenance on your roads and magrails.
More Inforamtion here
There is no Tech for it. You can check by going here and searching for "road".