Aerial fiber hangs on utility poles; underground fiber is buried in conduit. Aerial is usually cheaper and faster to build where poles already exist; underground costs more upfront but hides the network from storms, vehicles, and time. Nearly every real network is a hybrid, chosen span by span.
The economics
Aerial construction rides infrastructure someone already built — but renting space on poles means pole attachment agreements, engineering surveys, and make-ready: paying to move existing lines to create clearance. Make-ready is aerial's hidden cost and its hidden schedule risk, since the pole owner's crews do the moving. Underground trades that dependency for construction cost: more per foot, no landlord, and restoration to pay for. In dense rock or under finished streets the premium is real; in open soil, plowing narrows the gap dramatically.
Resilience and lifespan
Underground wins the weather argument: ice storms, hurricanes, and car-vs-pole accidents take aerial spans down and leave buried plant untouched. Underground's enemies are different — excavators that dig without locates, and water in badly sealed enclosures. Well-built plant of either kind runs decades; the glass itself doesn't wear out.
Rules of the road differ by state too — pole-attachment law, ROW depth standards, one-call regimes — which is exactly what our state-by-state pages document.
How the choice actually gets made
Designers walk the route and price both: pole line in good shape with room on it — aerial. No poles, hostile make-ready, storm-critical route, or a jurisdiction that requires burial — underground. Then the splice points, handholes, and transitions get engineered so the two halves behave as one network.