While during a race there may be many occasions where an AI car can simply drive according to its specified racing line and speed oblivious of any other factors, it will regularly need to take account of other vehicles and events and adapt its strategy accordingly. 

For example, the following circumstances may dictate a modification to the standard racing line model:

• A slower car ahead that is to be overtaken.
• A car behind that is to be blocked.
• A potential collision with a car alongside that is to be avoided.
• A stationary obstruction on the track (debris, crashed car) that is to be navigated around.
• A car immediately in front that is to be drafted.
• Car damage, worn tyres or low fuel that suggest the need to pit.
  

Managing these interactions successfully is of course a crucial element of developing a realistic vehicle AI system. The Drivatar system in Forza did not implement the above behaviours directly, but rather provided an API-like functionality for external modules to over-ride choice of line and speed in a smooth credible manner. For example, the system might implement functionality such as "move out three metres to the left and increase target speed by an additional 5%". 

The actual sub-system to manage the higher-level race strategy scenarios was developed elsewhere within Microsoft Games Studios, and as such, we cannot offer any further detail here.