A computer-implemented method comprising: transmitting a message by a Traffic Broadcast System, the message comprising a location (50), a traffic pattern code (50) and a time period of validity (50); receiving the message by a Navigation System; and selecting a first traffic pattern (244, 602) stored in a geographic database, wherein the first traffic pattern (244, 602) is selected based on a current time period, represents an expected traffic speed for a first location (50) on a section of a road network for the current time period, and is identified by a first traffic pattern code (50); using the first traffic pattern (244, 602) to perform a navigation system function associated with travelling in the section of the road network; receiving a message from the Traffic Broadcast System including a second traffic pattern code (50) which identifies a second traffic pattern (602, 244) stored in the geographic database, the second traffic pattern (602, 244) representing an expected traffic speed for a second location (50) on the road network for the current time period, the second location (50) being different from the first location (50) on the road network; during a specified time period of validity (50) for the second traffic pattern (244, 602), using the second traffic pattern (602, 244) to perform the navigation system function associated with travelling in the section of the road network; and after expiry of the time period of validity (50), reverting to using the first traffic pattern (244, 602) for performing the navigation system function associated with travelling in the section of the road network. transmitting a message by a Traffic Broadcast System, the message comprising a location (50), a traffic pattern code (50) and a time period of validity (50); receiving the message by a Navigation System; and selecting a first traffic pattern (244, 602) stored in a geographic database, wherein the first traffic pattern (244, 602) is selected based on a current time period, represents an expected traffic speed for a first location (50) on a section of a road network for the current time period, and is identified by a first traffic pattern code (50); using the first traffic pattern (244, 602) to perform a navigation system function associated with travelling in the section of the road network; receiving a message from the Traffic Broadcast System including a second traffic pattern code (50) which identifies a second traffic pattern (602, 244) stored in the geographic database, the second traffic pattern (602, 244) representing an expected traffic speed for a second location (50) on the road network for the current time period, the second location (50) being different from the first location (50) on the road network; during a specified time period of validity (50) for the second traffic pattern (244, 602), using the second traffic pattern (602, 244) to perform the navigation system function associated with travelling in the section of the road network; and after expiry of the time period of validity (50), reverting to using the first traffic pattern (244, 602) for performing the navigation system function associated with travelling in the section of the road network.