The attribute for each link in the network play a key role in defining how the link is used in the routing calculations. This is defined through a bit-pattern:
0-31: Defines road class. These have no predefined meaning, but their value is translated into a drivetime during network load by using the speed information from the INI file.
Add 32 if mode 1 isn't allowed on this link.
Add 64 if mode 2 isn't allowed on this link.
Add 128 if mode 3 isn't allowed on this link.
Add 256 if mode 4 isn't allowed on this link.
Add 512 if it is a one-way street, which may not be travelled in the opposite of the digitised direction.
Add 1024 if it is a one-way street, which may not be travelled in the digitised direction.
Add 2048 if a link is part of a roundabout. This is used for generating driving directions. See RouteList.
Add 4096 if a link is a "non-driving" link. This can be used to mark ferries and car trains, so their length is not included in driving directions. See RouteList.
Add 8192 if it is not allowed to make U-turns at the From-end of the link.
Add 16384 if it is not allowed to make U-turns at the To-end of the link.
32768 is reserved for future use.
An example:
A road of class 4, which can only be travelled in the direction of digitization: 4 + 512 = 516.