STISIM Drive (SDL) - C - Curve
Display a constant radius
curve in the roadway display. This event describes the roadway that will appear
on the display screen. Positive values of curvature will display the curve to
the right and negative values display curves to the left. Each curve is limited
to a total of 180 degrees (curve length multiplied by the curvature) and curves
that are specified greater than 180 degrees will cause a warning to be
displayed and will be ignored. There is a very important limitation
that you must abide by when using the roadway curvature event:
You must make
sure that the previous curvature has been completely negotiated before you
begin displaying a new curve.
EVENT PARAMETERS:
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PARAMETER 1: |
The longitudinal distance, in feet, that the beginning of the curve is away from the driver when the curve first appears. |
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PARAMETER 2: |
Entry spiral length in feet. An entry spiral is a transition section of roadway from a straight section of road to a curve. The spiral will linearly change the roadway curvature from zero (straight) to the curvature of the curve (parameter 5) over the spiral length. Spirals are used on real roads to ease the drivers transition into curves. Note: the spirals must be specified in whole numbers of feet. |
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PARAMETER 3: |
The longitudinal length, in feet, of the curved section of roadway. |
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PARAMETER 4: |
Exit spiral length in feet. An exit spiral is a transition section of roadway from a curve to a straight section of road. The spiral will linearly change the roadway curvature from curvature of the curve (parameter 5) to the zero (straight) over the spiral length. Spirals are used on real roads to ease the drivers transition out of curves. Note: the spirals must be specified in whole numbers of feet. |
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PARAMETER 5: |
Constant roadway curvature (1 over the radius of curvature, 1/foot) that will be used when displaying the curved roadway section. A positive curvature means that the roadway will curve to the right while a negative value of curvatures means the roadway will curve to the left. |
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PARAMETER 6: |
This parameter is a flag for enabling and disabling roadway super elevation. Set this parameter to one of the following: 0 - No super elevation Super elevation is the cross-slope of the roadway driving lanes while you are in a curve. In general the roadway lanes have a slope to them that is defined using the cross-slope parameter in the ROAD event. What this parameter does is allows you to override the cross-slope parameter and allows you to specify a new cross-slope for this curve. The magnitude of the cross-slope is specified with parameter 7. This is an optional parameter and is not required. You should also note that the shoulder and foreslopes are not affected by super elevation. |
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PARAMETER 7: |
Curve's super elevation or cross-slope measured in percent grade (100 * ft/ft). A negative value causes the travel lanes of the roadway to be banked with the curve (this helps the driver). |
EXAMPLES:
5000,C,
1000,100,500,100,.0025
9000,C, 1000,50,500,50,-.0025
When creating your
simulation environment, it is wise to design the roadway layout before you
actually begin placing events in the scenario. There are 2 choices for defining
sections of the roadway, curved and straight (by default). If you do not use
the C event, then all you will have is a long straight section of roadway.
Therefore, the C event is primarily used to force the driver to negotiate
curves by steering the vehicle through them.
The 2 examples events
above, show how you would define right and left curves in the roadway display.
The roadway will remain straight until the start of the curve is reached, and
then will bend in the direction specified. In the above examples, the curves
are shown when the driver has driven 5000 and 9000 feet down the road, and it
appears 1000 feet in front of them. In both cases, the length of the curve is
500 feet and the radius of curvature is 400 feet (1/0.0025). The first curve
has 100 foot entry and exit spirals, and curves to the right, while the second
curve has 50 foot entry and exit spirals and curves to the left.