According to the Indian Roads Congress (IRC 86: 2018) guidelines, the extra widening of curves is based on the following parameters:
1. Horizontal curve radius:
The extra widening of a road curve increases with the horizontal curve radius. A smaller curve radius requires more widening to accommodate the vehicle's turning radius. Hence, statement (A) is correct.
2. Number of lanes:
The number of lanes affects the widening of the curve. More lanes lead to a higher need for extra widening as the width of the carriageway increases. Therefore, statement (C) is also correct.
Thus, the correct answer is (A) and (C).