3-bounded property in a triangle-free distance-regular graph

Let Γ denote a distance-regular graph with classical parameters ( D , b , α , β ) and D ≥ 3 . Assume the intersection numbers a 1 = 0 and a 2 ≠ 0 . We show that Γ is 3-bounded in the sense of the article [C. Weng, D -bounded distance-regular graphs, European Journal of Combinatorics 18 (1997) 211–229].