Barrier penetration is attributed to energy fluctuations expected from the uncertainty principle. Numerical simulations are made by calculating the traversal time and action for a large number of possible velocity profiles. Distributions of traversal time are determined by assuming that the probability of each velocity profile decreases exponentially with the action of the fluctuation it requires. Distributions of traversal times are reported for rectangular barriers having different sizes. For large barriers the distributions are leptokurtic and centered at the semiclassical traversal timeT0=d&sqrt;m/[2(V0−E)], wheredandV0are the length and height of the barrier andmandEare the mass and energy of the particle. The kurtosis decreases and the mode shifts to shorter durations with decreasing barrier size.