The availability of large-scale air traffic data,including aircraft operating at very low levels, opens newpossibilities for a quantitative evaluation of the risk of midair collisions for drones, esp. in beyond visual line-of-sightoperations. The contribution of this paper boils down to a threefold evaluation of such a risk using the reference qualitativeapproach, the Specific Operations Risk Assessment (SORA),and two quantitative approaches inspired from the literature.Quantitative assessment makes the most of the data collectedthrough cooperative technologies such as ADS-B and FLARMby estimating distributions and indicators from real data insteadof using generic assumptions. In the following, we perform riskanalyses of a realistic drone inspection mission along fast-trainlines, and show how the quantitative analysis of the air riskcould help to determine when such a mission could be executedin conformance with the existing framework of SORA.