Optimal transportation provides a means of lifting distances between points on a geometric domain to distances between signals over the domain, expressed as probability distributions. On a graph, transportation problems can be used to express challenging tasks involving matching supply to demand with minimal shipment expense; in discrete language, these become minimumcost network flow problems. Regularization typically is needed to ensure uniqueness for the linear ground distance case and to improve optimization convergence; state-of-the-art techniques employ entropic regularization on the transportation matrix. In this paper, we explore a quadratic alternative to entropic regularization for transport over a graph. We theoretically analyze the behavior of quadratically-regularized graph transport, characterizing how regularization affects the structure of flows in the regime of small but nonzero regularization. We further exploit elegant second-order structure in the dual of this problem to derive an easily-implemented Newton-type optimization algorithm.Transport over graphs has a rich history and has been considered in mathematics, operations research, computer science, and many other disciplines. At the broadest level, this problem is a slight generalization of the linear assignment problem and can be solved using several classical techniques; see e.g. [6,4] for discussion.Without regularization, the particular problem we study would be an instance of minimum-cost flow without edge capacities.[30] discusses classical algorithms for this linear programming problem, such as the cycle canceling [20], network simplex [28], and Ford-Fulkerson algorithms [15]. Classical methods such as these often are not accompanied with systematic "tie-breaking" strategies in case the network flow is non-unique, indicating the potential application of a strictly convex variation of the problem such as ours.The theoretical computer science community recently has reconsidered this class of problems from an optimization perspective. In the undirected, capacity-free case, [36] proposes a preconditioner for approximate minimum-cost flow problems that achieves nearly-linear runtimes.[10] considers the more general case of minimum-cost flow in directed graphs with unit capacities, extending a framework proposed in [26] for approaching graph-based problems using the interior point method. These algorithms are primarily of theoretical interest but do employ interior point-style methods, possibly implying a systematic choice of flows in the case of multiple optima.In the continuum, the theory of optimal transport [42] classifies problems structured similarly to minimum-cost flow as the 1-Wasserstein distance or Beckmann problem [1]. See [33] for analysis and [42,17,32] for theoretical discussion. Even over general spaces, solutions of the 1-Wasserstein problem generally are nonunique and include some degenerate optima [42, §2.4.6]. Numerical algorithms for these problems include [39], which uses finite element methods for a vector field ver...