Unmarried women who cover their hair for modesty or religious reasons....?

In religious traditions which require married women to cover their hair, is there a provision or custom for women who remain (or later become) unmarried? i.e. Would an Orthodox Jewish widow stop covering her hair while she remained unmarried? Do women who remain single start covering their hair when they reach a "certain age" beyond which long, loose hair would be improper? Is there an intermediate step such as the severely pulled back bun or a half-snood like cowl?