The ornamental design for an electric powertransmissionlinesupport tower, as shown and described.
FIG. 1 is a perspective view of an electric power transmission line support showing our new design;
FIG. 2 is a left side elevational view thereof;
FIG. 3 is a front elevational view thereof, the rear elevational view being a mirror image;
FIG. 4 is a top plan view thereof; and,
FIG. 5 is a bottom plan view thereof.
The broken lines in the drawing figures are provided only to indicate the environment in which the design is associated, and form no part of the claimed design.