old Japanese coin, both, counter for vehicles, two
兩 centers on the idea of a pair or duality: two of something, both sides, or a matched set. The meanings 'old Japanese coin' and 'counter for vehicles' are specific historical applications of this two-ness, likely from a coin denomination or a vehicle's paired wheels.
兩 is the traditional form of 両. It originally depicted a pair of yoked horses or a balanced scale, symbolizing two matched things. The modern simplified form 両 is more common in Japanese.
The top line and the symmetrical inner strokes suggest a balanced pair, like two sides of a scale or two horses under a yoke. 兩 is two of something, both together.
For リョウ, imagine a pair of old Japanese ryō coins: ryō -> リョウ, and the two coins represent both sides of the currency.