Look up deterioration curve and maintenance curve (J shaped) for hard infra. TLDR is asset stays in good condition for 75% of lifetime i.e. decades with light maintenance (flat part of J). By roads I mean highways where most of the expense / work is in building out the base / sub base (i.e. ballasts for rail), that last decades. US is uniquely bad maintained/prevention but even then major assets do not deteriorate on GPU timeline.