Enabling traffic allows the Routing API to consider up-to-date traffic information when calculating a route. Additionally, this live traffic information is augmented with historical traffic speeds when considering travel times in the future. A route calculation for the current time will use live traffic information. For longer routes, the live traffic information will be mixed with historical traffic information for the later portions of the route. Routes calculated for future times will use historical traffic information to determine traffic speeds, as well as considering any long-term road closures on the route. If the request does not include a departure time, then all current live traffic events (at the time of calculation) will be assumed to be valid for the entire length of the route. No time-dependent information will be used.
You can only enable traffic information for some types and transport modes, as described in Routing Mode Parameter Combinations.