A bearing passes the superstructure's reaction to the pier while letting the deck rotate and, where required, translate. Every bearing layout is an articulation scheme: which supports are fixed, which are guided, which are free, chosen so that temperature can move the deck without fighting itself and seismic or braking force has a defined path to the ground.

• Elastomeric bearings, layers of rubber bonded to steel shims. Cheap, maintenance-free, accommodate rotation and moderate translation by shear deformation. The default for spans under about 50 m and reactions to a few meganewtons.
• Pot bearings, a rubber disc confined in a steel pot, taking large loads and rotations; sliding PTFE-on-stainless surfaces add translation.
• Spherical and disc bearings, for large rotations and very large loads, long-span and railway bridges.
• Rocker and roller bearings, historical steel bearings that seize with corrosion; the locked bearing is a classic cause of unintended forces and cracked piers.

Design a bearing to be replaced: leave jacking points and clearance, because it will be.

Joints let the deck breathe and are the single most damaging component on a bridge: when they leak, salt water runs onto the girder ends, bearings and pier caps below, and that is where most of the deterioration in a cold-climate bridge is found. The first design decision is therefore how many joints can be eliminated, by continuity, by integral abutments, by link slabs.

Where a joint is unavoidable, its type follows the movement: asphaltic plug joints for a few tens of millimetres, strip seals (a rubber gland between steel extrusions) to about 100 mm, modular joints with several seals for movements of hundreds of millimetres on long bridges, and finger joints where large movements must carry heavy traffic. Movement is computed from temperature range, creep and shrinkage, and, in seismic zones, from the design displacement; installation temperature sets the gap.

Water is the enemy, and drainage is the defence that costs least and is neglected most. A deck is crowned or cross-sloped at about 2% and graded longitudinally so that water reaches inlets (scuppers) sized for the design storm; downspouts then carry it clear of girders, bearings, piers and the ground below the abutments. Deck ends drain away from the joint; girder bottom flanges have drip grooves; box girders have vents and drains in every cell.

Inspections consistently find the same faults: scuppers blocked with debris, downspouts discharging onto pier caps, and joints leaking, each one a maintenance item that turns into a structural one.

Two design rules cover most of it. Inlets every 20–30 m on a 2% longitudinal grade, closer where the grade flattens; and no free discharge onto anything below: piers, girders, bearings, railways, roads or navigable water all need piped drainage to the ground. Inspectors should be able to reach every scupper and every cleanout.

Barriers keep vehicles on the bridge. Modern barriers are not designed by calculation but by crash test: MASH (formerly NCHRP 350) test levels TL-1 to TL-6 define the vehicle, speed and angle, and a barrier is qualified at a level, TL-4 for most highways, TL-5 where heavy trucks are frequent. The concrete F-shape and single-slope profiles, and steel post-and-rail systems, are the common qualified shapes.

What the designer calculates is the deck overhang that carries the barrier: AASHTO Section 13 gives the transverse and longitudinal collision loads that the overhang and its reinforcement must resist, and, as Chapter 6 noted, they usually govern the overhang design. Pedestrian and bicycle railings have their own height and load rules.

Bridges carry more than traffic: water mains, gas, power, telecoms, lighting and signs. Each is a permanent load (DW), some are dynamic (a bursting main is a real event), and all need access for the utility's own maintenance without closing the bridge or damaging it. Attachments are the fatigue details nobody designed; a sign bracket welded to a girder flange is a Category E' detail waiting for a crack.

Inspection access, walkways in box girders, ladders in towers, catwalks under decks, gantries on long spans, is designed in from the start on well-run projects and improvised for decades on the rest.

Utilities also decide inspection access and, in the worst case, the failure mode: fires fed by a utility corridor have destroyed decks, and gas mains are kept outside enclosed boxes for that reason.