Roads are essentially a city's 'power lines'. With the exception of decorations, all buildings must be touching a road that is connected to the Town Hall in order to produce coins, supplies, train military units, etc. Any building not touching a road with at least one of its edges will display a graphic of a broken chain above it and will cease all productivity. For players' convenience, roads may be replaced with roads of a different type by simply building over the existing road with no need to delete/sell it first. However, roads also give nothing back when sold so try to preserve them as much as possible when placing/moving buildings rather than destroying and replacing them.
Two lane roads
In the Progressive Era and beyond, some buildings will require a two-lane street instead of an ordinary road; a single-lane road cannot be used to connect these buildings and will be ignored by them. On the other hand, a street can be used to connect any building, even those that only require an ordinary road. Streets are quite expensive to place and require a lot of space, so careful planning should be taken to maximize their effectiveness. It should also be mentioned that, although a road may touch a street and use that to connect to the Town Hall, the opposite is not true - a street must always connect to the Town Hall directly. If a street is not connected directly to the Town Hall, it may not be used to connect buildings that require one but will still function as a normal road. On top of that, individual streets may only be connected to one street on any single side. This can make turning difficult, as streets cannot be built 'between' squares when building in a direction away from the rest of the street.
When placing roads, the most efficient strategy is to use long straight lines and to place buildings along the roads with their short sides touching them. Arrange your buildings in rows or columns two buildings wide, and place roads on both sides of each row/column. A road with many twists, turns, and dead ends, or a building with roads touching more than half of its edges, is considered inefficient and should be avoided by players wishing to make the best use of their building space. When placing streets, keep in mind their special restrictions outlined above as well.
For more tips on how to layout roads refer to the Guide to maximising space
Observe that all ages don't have new road types