Titan TTS2 Manual page 95

interface of "Define(H)-Begin", then you can select the other lie type
to input. After finishing the input, press [ENT] to enter the interface
of "List of H curve";
Note: Do not define the length as '0', which indicates ending the
alignment.
Input "Line":
Input "Circle":
The value of Radius (R) can be negative. The positive direction
is the right direction along the designed roadway, and the left is
negative. The "Len." refers to Arc length.
Input "Spiral":
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