Roads in Civilization V now have a maintenance cost. At a cost of 1gp/turn for roads and 2gp/turn for rail it adds up quick. This means that you need to choose carefully where you run roads and rail lines.

A good general design principle is to "think like a tree and leaf". Start at the center city, connect outwards to the nearest 3 cities. Then connect outwards from those 3 cities to their nearest neighbors. Only add cross-connects once you have a steady income surplus or you have a special need like a long border with the enemy where you need fast reaction across the front.

Here's a sample road network in one of my games (Fractal, Large). I've over-drawn the road network using a big purple line to make it more obvious.



Kagoshima to Osaka (in the lower right) road did not exist for a long time until I was making over 20 gold/turn regularly.

The roads from London to Warrick and Newcastle were laid down by the AI - and the AI did a good job.

Note that Satsuma-Kyoto is not highlighted in yellow any more. That road used to be what the trade network ran across, until Satsuma added in a Harbor. Now the trade traffic apparently goes via sea lanes to another city with a Harbor (probably Nara or Kyoto).