  An updated catalog of 205 observed tangents to the spiral arms (in Galactic
longitudes) since 1980 is presented. This represents an addition of 80 arm
tangents in 6 years (since 2016). Most arm tangents are observed at telescopes
in the radio regime. In this study, the separation of each arm tracer from the
dust lane is analyzed to obtain the relative speed away from the dust lane (an
age gradient). Each arm tracer is observed to be separated from the dust lane,
showing an age gradient of about 11.3 +/- 2 Myr/kpc across the spiral arm; this
gives a relative speed away from the dust lane of about 87 +/- 10 km/s.
