Several parts combine into one character.

通 is a phonetic-semantic compound: 辶 (the "going" radical, a foot moving along a road) plus 甬 (a tunnel / passage, providing both sound and the sense of "open path"). Together they form the picture of movement through an unobstructed channel — "to pass through, to communicate, to flow without blockage." This single character covers a remarkable conceptual sweep: physical traffic, telecommunication, mutual understanding, and "ordinariness" (because what is unobstructed is what is universal).

Korean reading "tong." Saturates everyday Sino-Korean vocabulary: 通信 (tongsin, telecommunication), 交通 (gyotong, traffic / transportation), 普通 (botong, ordinary / usual), 通過 (tonggwa, passing through), 共通 (gongtong, common / shared), 通報 (tongbo, notification). The native-feeling word (sotong, communication / mutual understanding) is also Sino-Korean — 疏通 — and underlies modern Korean discourse about social communication.

Mandarin tōng, 1st tone. One of the highest-frequency Sino-Chinese morphemes: 通过 (tōngguò, to pass / by means of), 交通 (jiāotōng, traffic), 通知 (tōngzhī, notice), 沟通 (gōutōng, communicate), 普通 (pǔtōng, ordinary), 普通话 (pǔtōnghuà, "common speech" — Standard Mandarin). The fact that the official name for Mandarin uses 通 reflects the ideal of a language that "flows everywhere unobstructed."

Japanese on-reading ツウ (tsū) — 交通 (kōtsū, traffic), 普通 (futsū, ordinary), 通信 (tsūshin, communication), 通常 (tsūjō, normally). Two distinct kun-readings split semantically: とおる (tōru, "to pass through") for the physical sense — 道を通る (to pass along a road); and かよう (kayou, "to commute / go regularly") for the recurring-movement sense — 学校に通う (to attend school regularly), 病院に通う (to make regular hospital visits). The kayou form has no exact English equivalent — it specifically denotes habitual back-and-forth movement.

Memory aid: the "going" radical (辶) plus a passage (甬) — moving through an open channel.