traffic, pass through, avenue, commute, counter for letters, notes, documents, etc.
通 centers on movement along a path: traffic, passing through, commuting, or an avenue. The counter sense extends this to items that travel along a route, like letters or documents.
normal; ordinary; regular; usual; common; average
in accordance with; following
street; road; avenue; thoroughfare
usual; ordinary; normal; regular; general; common
to go by; to go past; to go along; to travel along; to pass through; to use (a road); to take (a route); to go via; to go by way of
correspondence; communication; transmission; news; signal; telecommunications
traffic; transportation
common; shared; mutual
to stick through; to force through
authority; expert; connoisseur; well-informed person
to go to and from (a place); to go back and forth between; to run between (e.g. bus, train, etc.); to ply between
online shopping; e-commerce; mail order
notice; notification; report; posting
currency
passing through (a tunnel, station, town, etc.); passing by (e.g. of a typhoon); transit
(bowel) movement; evacuation; defecation
commuting to work
report; notification; tip; bulletin
circulation (of money, goods, etc.); distribution
telephone call; speaking over the telephone; (Internet) voice call; videoconference call
commuting to school; school commute
passage; pathway; roadway; avenue; aisle
unobstructed view; perspective; visibility; vista
(common) use (of a language, currency, etc.); current use; circulation; currency; validity (e.g. of a ticket)
通 combines 辶 (movement) with 甬, which likely contributes the sound and the idea of a through passage. The character originally expressed going through or penetrating.
The movement radical 辶 wraps around 甬, like a road passing through a tunnel. Traffic flows along this avenue, and letters commute through it.
For ツウ, imagine a two-lane tunnel where traffic passes through: two -> ツウ, and the road 辶 goes straight through 甬.