A five-year program to improve worker safety at Yellowstone National Park has yielded significant results, but more work is needed, park officials say.

After OSHA in 1997 noted 600 violations, including 92 citations for problems deemed serious, the park and OSHA formed a partnership to deal with safety issues.

The partnership, which ended last month, led to major improvements in correcting violations and changing attitudes about health and safety, OSHA and park officials say.

Yellowstone invested $500,000 on safety equipment including vests and hard hats, employee training, and improvements such as better ventilation for employees working around cars and snowmobiles.