Green’s Dictionary of Slang

(Aus.) the road as followed by an intinerant, the underlying image presumably linked to the sundowner n. (1) who tends to arrive at a destination around sunset.

1894		H. Lawson in Worker (Wagga, NSW) 11 Aug. 2/5: He turned half-back to the counter, hooked his elbow on it, and gazed out through the door along Sunset Track.
1898		West Australian (Perth) 5 Feb. 9/3: He was now Bob Edwards, the unkempt tramp, humping his bluey along the Sunset Track, shunning respectable folk and all that was theirs.
1908		Critic (Adelaide) 17 June 21/4: Better for you the sunset track, with the sun blood-red behind.
1911		Advertiser (Adelaide) 7 Jan. 19/8: The man, cramped by city life, feels an imperative call ‘to leave his bones on sunset track’.
1925		Richmond River Herald (NSW) 20 Jan. 1/4: On the sunset track that leads out West, where tin roofs blister under the sweltering heat, and men’s parched tongues reproach the quality of the liquor they supply outback.
1927		News (Adelaide) 28 Dec. 6/3: We miss the grand old stalwarts who trod the Sunset Track.