Hi Heather,

the only way to do this using the driveway tool is inserting different segments and change the width of each segment

The detail tab will not help to solve this. Because the feature --> convert to doesn't convert closed polygons

Instead of this you can use the Ground fill region (second icon of the landscape tool, see attached)
With this tool, you can draw any polygon, adjust curves etc--> texture it (you can use the same texture of the driveway if you wish) and it will look like the driveway (see attached)

Of course, if you wish to add thickness, use the floor tool

Hope this helps

Patricia