Why the diagram needs two views

Stand at the side of the bridge and the second pylon leg is directly behind the first, with its whole cable plane hidden. No amount of detail in the side view recovers that — it needs a second view.

LOOKING FROM THE SIDE

The far leg is exactly behind the near one. Its cables land on the same points. You cannot tell there are two.

→

LOOKING FROM THE FRONT

Two legs, two cable planes, the deck passing between them. Only this view shows it.

The naming comes from BMS, not from us

BMS already models a two-legged support — portal_pier.blade.php. A pylon is the same thing, taller:

let pierLeftKey  = 'pl_' + pierNumber;      // each leg is its own location
let pierRightKey = 'pr_' + pierNumber;
let totalLeft  = …pier_height_l;              // each leg its own height
let totalRight = …pier_height_r;
this.addLabel(leftColX  + columnWidth/2, centerY, 'L', '16px');
this.addLabel(rightColX + columnWidth/2, centerY, 'R', '16px');

So the pylon reuses it wholesale

Pylon (Lower/Upper) → pl_2 · pr_2
Stay Cable → pl_2 · pr_2
item a1_cable_1 · a2_cable_1
Cross beam → p_2 (spans both)

Don't confuse this with LHS / RHS

In BMS, LHS/RHS means two separate carriageways with their own component IDs (PileLhs, GirderLhs), used only when carraige_way = separate. Mindhola is a single deck with a median — common carriageway. The pylon's two sides are legs (L/R), not carriageways.

Front view at a pylon — the detail

Every dimension comes from a field already on the form.

Dimensions

Deck detail, front view

4-lane common carriageway with a median. Note these are lanes, not BMS LHS/RHS components.

Front view at an ordinary pier — for comparison

Approach span: a girder grid on a pier cap. No legs, no cables — one location key p_7.

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