For a strongly connected digraph D the restricted arc-connectivity λ′(D) is defined as the minimum cardinality of an arc-cut over all arc-cuts S satisfying that D - S has a non-trivial strong component D₁ such that D-V (D₁) contains an arc. Let S be a subset of vertices of D. We denote by $ω^+$(S) the set of arcs uv with u ∈ S and v ∉ S, and by $ω^−$(S) the set of arcs uv with u ∉ S and v ∈ S. A digraph D = (V,A) is said to be λ′-optimal if λ′(D) = ξ′(D), where ξ′(D) is the minimum arc-degree of D defined as ξ(D) = min{ξ′(xy): xy ∈ A}, and ξ′(xy) = min{|$ω^+$({x,y})|, |$ω^−$({x,y})|, |$ω^+$(x) ∪ $ω^−$(y)|, |$ω^-$(x)∪$ω^+$(y)|}. In this paper a sufficient condition for a s-geodetic strongly connected digraph D to be λ′-optimal is given in terms of its diameter. Furthermore we see that the h-iterated line digraph $L^h$(D) of a s-geodetic digraph is λ′-optimal for certain iteration h.