Attention is an important component of the driving task. When a subtask has a low demand, it can be performed with little conscious attention, allowing the driver to allocate attention to tasks that require more cognitive resources. When the demands of the driving task require more attention be placed on a particular subtask, it comes at the expense of performing tasks requiring a higher level of attention. This process is known as

load shedding

. For example, a driver on an uncongested freeway can easily perform navigational subtasks. If traffic becomes extremely congested, the navigational subtasks become more difficult to perform because the driver must allocate more attention to the control and guidance subtasks.

Expectation is also very important in the driving task. Drivers need to have a reasonable expectation about how their vehicles will perform, the geometry of the road downstream of their positions, and where to find navigational information. If the expectation of the driver is violated, the performance of the driving task may suffer. This situation is particularly important in freeway guide signing where the unfamiliar driver will rely on guide signs to provide information to perform the navigation subtask.