Double-triangular Distribution is the combination of two triangles, each with an area of 0.5. The mode is also the median.
The variance is:
Note: the variance is the same as for the triangular distribution.
The probability density is:
And the cumulative distribution function:
The double-triangular is quite unnatural. It is highly unlikely to be a proper representation of uncertainty. Moreover, estimating the median is, in my view, more difficult than the estimating the most likely value (mode).