Wyo. Stat. § 15-4-307
Any person who renders a street insufficient or unsafe for travel by any excavations or obstructions not authorized by law or ordinance, or is negligent in the management of any authorized excavation or obstruction, or fails to maintain proper guards or lights is liable for all damages recovered by any person injured as a result of the obstruction or negligence. No action may be maintained against the city or town for damages unless the person or persons creating the condition are joined as parties defendant. In case of judgment against the defendants, execution shall at first issue only against the defendant causing the insufficiency or danger, and the city or town is not required to pay the judgment until that execution is returned unsatisfied. If the city or town pays the judgment, it is the owner thereof and may enforce its payment from the other defendants. The city or town is also entitled to execution against them and to take such other proceedings as judgment creditors are entitled to take.
W.S. 15-4-307