  Over the past decade, the BeSSeL Survey and the VERA project have measured
trigonometric parallaxes to approximately 250 massive, young stars using VLBI
techniques. These sources trace spiral arms over nearly half of the Milky Way.
What is now needed are accurate distances to such stars which are well past the
Galactic center. Here we analyze the potential for addressing this need by
combining line-of-sight velocities and proper motions to yield 3D kinematic
distance estimates. For sources within about 10 kpc of the Sun, significant
systematic uncertainties can occur, and trigonometric parallaxes are generally
superior. However, for sources well past the Galactic center, 3D kinematic
distances are robust and more accurate than can usually be achieved by
trigonometic parallaxes.
