A framework to engineer existing structures, in particular bridges, and novel engineering methods and technologies are presented to extend the service duration of existing bridges while meeting the requirements of modern use. Accurate determination of bridge behavior using data from in-situ measurements and long-term monitoring of traffic action effects allow to verify realistically the structural and fatigue safety of bridges. If interventions are necessary, a targeted use of advanced high-performance materials such as UHPFRC allows to rehabilitate and strengthen effectively reinforced concrete bridges. This approach follows the principle to preserve material resources and their embodied energy, thereby limiting greenhouse gas emissions to a minimum when requalifying and adapting existing bridges to future use.