Among other things, the map illustrates on which roads truck bans apply, which roads are exempt from the bans, and which roads may be used as an alternative when bans are in force.
The key in the top left of the map shows that roads with truck bans are marked in thick red, with roads that are exempt marked white with red edges. The green roads are alternative routes to those roads with bans.
The map can be downloaded in pdf format here.