  Graphene on hexagonal boron nitride (hBN) can exhibit a topological phase via
mutual crystallographic alignment. Recent measurements of nonlocal resistance
($R_{nl}$) near the secondary Dirac point (SDP) in ballistic graphene/hBN
superlattices have been interpreted as arising due to the quantum valley Hall
state. We report hBN/graphene/hBN superlattices in which $R_{nl}$ at SDP is
negligible, but below 60 K approaches the value of $h/2e^{2}$ in zero magnetic
field at the primary Dirac point with a characteristic decay length of 2
${\mu}$m. Furthermore, nonlocal transport transmission probabilities based on
the Landauer-B\"uttiker formalism show evidence for spin-degenerate ballistic
valley-helical edge modes, which are key for the development of valleytronics
