How can I route an in wall dryer vent through double top plate?
2015 INTERNATIONAL RESIDENTIAL CODE
CHAPTER 15
EXHAUST SYSTEMS

M1502.2 Independent exhaust systems.
 Dryer exhaust systems shall be independent of all other systems and shall
convey the moisture to the outdoors.

M1502.3 Duct termination. 
Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer’s installation instructions. If the manufacturer’s instructions do not specify a termination location, the exhaust duct shall terminate not less than 3 feet (914 mm) in any direction from openings into buildings. Exhaust duct terminations shall be
equipped with a backdraft damper. Screens shall not be installed at the duct termination.

Answer.
You can go up or down. It's not advised to cut thru both top plates. The sole plate penetration is prefered. A cleaning access panel is not needed as cleaning can be performed from termination or connection point providing its installed to code.

M1502.4.1 Material and size.
 Exhaust ducts shall have a
smooth interior finish and be constructed of metal having
a minimum thickness of 0.0157 inches (0.3950 mm) (No.
28 gage). The duct shall be 4 inches (102 mm) nominal in
diameter.

M1502.4.2 Duct installation.
 Exhaust ducts shall be supported at intervals not to exceed 12 feet (3658 mm) and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8 inch (3.2 mm) into the inside of the duct.

M1502.4.5.1 Specified length.
 The maximum length of the exhaust duct shall be 35 feet (10 668 mm) from
the connection to the transition duct from the dryer to the outlet terminal.