The Transitions settings control how fast the steering angle changes into and between turns. By default the rate at which the steering can be turned is limited. This reflects the real life situation in which the vehicle is moving while the steering lock is being applied.
You can select Limit Forward Turn Rate or Limit Reverse Turn Rate to prevent instantaneous application of lock while travelling forwards or backwards respectively. Note that this setting can also be changed during driving if necessary.
The steering turn rate can be limited in one of three ways. Either by defining the speed of the vehicle which is then used in conjunction with the vehicles lock to lock time or, by explicitly defining the lock to lock distance (i.e. the distance travelled in the lock to lock time), or by the pure geometric calculation of a circular arc.
- Based Upon Lock To Lock Time imposes a turn rate that causes the turn radius to increase with speed. The turn rate (degrees per unit of distance) will be calculated as follows:
R = A/Vt
Where
- R is the maximum turn rate
- A is the maximum steering angle
- V is the design speed
- t is the lock to lock time
- Based Upon Lock To Lock Distance imposes a limit that is fixed for all speeds. The turn rate (degrees per unit of distance) will be calculated as follows:
R = A/d
Where
- d is the lock to lock distance
- The Based Upon Circular Tangential Arc setting causes the tracking point (typically the centre of the steered wheels) to follow a perfectly circular arc, irrespective of speed or lock to lock time. Note that this is the model used by several organizations to generate design vehicle turn templates (e.g. AASHTO, TAC). This mode can only be used with tracking points that are in front of (relative to the direction of motion) the minimum cut-in point.
The turn transitions can also be disabled automatically at changes of direction. You can select Turn On The Spot At Start Of All Forward Sections to automatically disable turn transitions when you stop reversing and start traveling forwards, or conversely, select Turn On The Spot At Start Of All Reverse Sections to disable turn transitions when you stop traveling forward and start reversing.
The setting Set Optimum Steering Angle At Start Of Path is used to set the best starting steering angle at the start of the path.