It is not obvious that forms of the type (wV)d meaning "to, towards" are related to this preposition (Arakelova 2001:22). They are united into a separate lexeme, see *ˀVd/d.
Throughout EthS this preposition exists only in combination with the element lV. In several languages adverbs of the *lVˁl- type are also attested: see Syr. ləˁal 'upward, above', Min. l-ˁl, 'upward (vers le haut)' (LM 31), Mnd. lilai 'upwards'. For the derivation from the PS root *ˁlw/*ˁly 'to go up' see Lipiński 1997:466, AED 109, Tropper 2000:766.