 The city is laid out so that arterial roads connecting inhabited clusters run through undeveloped areas of open land or forest, which results in a low population density; this also means that idle land is available for the development of future transport corridors if necessary without the need to build tunnels or acquire developed residential land.In contrast, other capital cities in Australia have substantially less green space.Canberra's districts are generally connected by parkways—limited access dual carriageway roads with speed limits generally set at a maximum of .