  We consider the problem of correct motion planning for T-intersection
merge-ins of arbitrary geometry and vehicle density. A merge-in support system
has to estimate the chances that a gap between two consecutive vehicles can be
taken successfully. In contrast to previous models based on heuristic gap size
rules, we present an approach which optimizes the integral risk of the
situation using parametrized velocity ramps. It accounts for the risks from
curves and all involved vehicles (front and rear on all paths) with a so-called
survival analysis. For comparison, we also introduce a specially designed
extension of the Intelligent Driver Model (IDM) for entering intersections. We
show in a quantitative statistical evaluation that the survival method provides
advantages in terms of lower absolute risk (i.e., no crash happens) and better
risk-utility tradeoff (i.e., making better use of appearing gaps). Furthermore,
our approach generalizes to more complex situations with additional risk
sources.
