The oldest method: build a temporary structure under the bridge, cast or assemble the permanent one on it, remove the temporary one. Falsework is economical where the ground is firm, the height is modest and nothing below must stay open, which describes most short viaducts and river bridges under 40–50 m span.

Falsework is also where construction accidents concentrate. It is designed by someone other than the bridge designer, often to a tighter budget, and it carries the full weight of wet concrete before the concrete has any strength. Injaka (South Africa, 1998) and the many scaffold collapses in the Failures library are the case for treating temporary works as real structures with their own reviews, and for the AASHTO Guide Design Specifications for Bridge Temporary Works.

Precast prestressed girders arrive by truck or barge and are lifted by crane, one or two mobile cranes for a road overpass, a floating crane for a river, then stabilised with temporary bracing until the diaphragms and deck tie them together. The critical moments are the lift itself (a slender girder can roll and buckle if picked at the wrong points) and the interval before bracing, when a wind gust has toppled more than one line of girders.

Where cranes cannot reach, a launching gantry straddles the piers and places girders span by span, moving itself forward on the completed deck, the method of long low viaducts and of urban metros. Erection tolerances, bearing seating and the sequence of deck pours (to control cracking over piers in continuous decks) are the details that make or break the schedule.

Start at a pier with a short pier-table segment. Hang a form traveller off each end. Cast a 3–5 m segment on each side, stress the cantilever tendons through the top slab, move the travellers, repeat. The two arms grow in balance so the pier is never seriously out of equilibrium, and the river, road or valley below is never touched. When the arms from adjacent piers meet, a closure segment joins them and continuity tendons in the bottom slab make the span a continuous beam.

Free-cantilever construction (FCM) built most of the world's concrete box-girder bridges between 70 and 300 m. Its engineering is in the stages: every segment changes the structure, the creep of concrete cast last month differs from concrete cast last year, and the deflection of the tip must be predicted so that the two arms meet at the right height. Unbalanced loads, one traveller ahead, a wind, an accidental drop, are checked with temporary pier fixity or props.

Cast the deck in 15–30 m segments in a fixed casting yard behind one abutment, and push the growing deck out over the piers on temporary sliding bearings. A light steel launching nose on the front reduces the cantilever moment as the deck reaches for the next pier. Every section of the deck passes over every pier, so the whole deck must carry both sagging and hogging moment during launching; it is prestressed centrally for the launch and then given its final tendons afterwards.

ILM needs a constant cross-section and a constant curvature in plan and profile (straight, circular or a single helix), spans typically 30–60 m, and a site where the casting yard can sit. In return it builds high viaducts and railway bridges over sensitive ground with almost nothing below the deck. Friction on the launching bearings sets the jack size; the launching nose and the pier-top guidance are the temporary works that matter.

An MSS is falsework that moves itself. A steel girder system, either under the deck or over it, carries the formwork for one full span, is supported on brackets at the piers, and after the span is cast and stressed it launches itself forward to the next. It suits long viaducts of 30–60 m spans with repetitive geometry, the standard-gauge railway viaducts of Europe and Asia and the elevated roads of the Gulf, where its high initial cost is spread over dozens of identical spans.

The deck can be cast span-by-span with a construction joint at about a fifth of the span past the pier, where the moment is near zero. The MSS itself, and the pier brackets it rests on, are the temporary works to review; a system launching in wind or with an uneven load has failed more than once.

Cast the box girder in 2–4 m segments in a yard, each against the previous one (match casting) so that the joints fit exactly, and assemble them on site with epoxy in the joint and post-tensioning through the segments. Erection is either span-by-span, a gantry holds all the segments of one span and they are stressed together, for viaducts of 30–50 m, or by balanced cantilever with a crane or gantry placing segments on each side of the pier for spans to about 150 m.

The method separates the slow part (casting) from the critical-path part (erection) and produces a factory-quality product; it built the Florida Keys, the Bangkok expressways, Dubai's and Doha's elevated roads, and much of the Hong Kong and Singapore rail network. Its risks are geometry control in the casting yard, where an error repeated over a hundred segments becomes a curve, and the durability of the joints and internal tendons.

Cable-stayed decks are built by cantilevering from the tower: each segment (steel, precast concrete or cast in a traveller) is added, its stay is installed and stressed, and the next follows. The stay forces are adjusted in stages so that the finished bridge has the intended geometry and force distribution, a problem solved by "backward analysis" from the target state. Side spans are often built on falsework first to hold the tower.

Suspension bridges go in order: towers, catwalks, main cable (aerial spinning wire by wire, or PPWS strands hoisted whole), cable bands and hangers, then deck segments lifted from barges by gantries riding on the cable, starting at midspan. The cable's shape changes as the deck is hung, so the sequence is planned so that the deck's curvature stays within what the joints can tolerate.

Arches are erected by cantilevering the ribs out on temporary stays from towers behind the abutments, or by building half-arches vertically and rotating them down; long-span steel arches have also been built by rotation in plan, cast the whole bridge parallel to a railway, then swing it 90° into place in a night. The Methods animations show each of these.