The growing space debris environment poses a significant threat to operational satellites and the future of spaceflight. To assess the collision risk between space objects, often probabilistic methods are used, which suffer from the fact that very uncertain states will lead to a low probability of collision, described as the dilution effect. Apart from this drawback, satellite operators are required to decide whether to mitigate a risk well before the time of closest approach. However, the time horizon available for this is often too short. This research aimed at studying whether novel risk assessment metrics could increase the reliability of risk quantification and extend the time horizon available for decision making. Outer probability measures have proven to be a reliable method for mitigating the dilution effect, whereas a geometry-based metric has proven more challenging to use. Together with the theoretical analysis of the metrics, their operational application has been studied.