diff --git a/src/document/spline-corridor-junctions.ts b/src/document/spline-corridor-junctions.ts
new file mode 100644
index 00000000..4c01e6a2
--- /dev/null
+++ b/src/document/spline-corridor-junctions.ts
@@ -0,0 +1,212 @@
+import { createOpaqueId } from "../core/ids";
+import type { Vec3 } from "../core/vector";
+
+export type SplineCorridorJunctionTerrainMode =
+  | "none"
+  | "paintOnly"
+  | "flattenAndPaint";
+
+export interface SplineCorridorJunctionConnection {
+  id: string;
+  pathId: string;
+  progress: number;
+  clipDistance: number;
+}
+
+export interface SplineCorridorJunction {
+  id: string;
+  kind: "splineCorridorJunction";
+  name?: string;
+  visible: boolean;
+  enabled: boolean;
+  center: Vec3;
+  radius: number;
+  materialId: string | null;
+  terrainMode: SplineCorridorJunctionTerrainMode;
+  connections: SplineCorridorJunctionConnection[];
+}
+
+export type SplineCorridorJunctionRegistry = Record<
+  string,
+  SplineCorridorJunction
+>;
+
+export const DEFAULT_SPLINE_CORRIDOR_JUNCTION_VISIBLE = true;
+export const DEFAULT_SPLINE_CORRIDOR_JUNCTION_ENABLED = true;
+export const DEFAULT_SPLINE_CORRIDOR_JUNCTION_RADIUS = 1.5;
+export const DEFAULT_SPLINE_CORRIDOR_JUNCTION_CLIP_DISTANCE = 1.5;
+export const DEFAULT_SPLINE_CORRIDOR_JUNCTION_MATERIAL_ID = null;
+export const DEFAULT_SPLINE_CORRIDOR_JUNCTION_TERRAIN_MODE: SplineCorridorJunctionTerrainMode =
+  "flattenAndPaint";
+export const MIN_SPLINE_CORRIDOR_JUNCTION_RADIUS = 0.05;
+export const MAX_SPLINE_CORRIDOR_JUNCTION_RADIUS = 500;
+export const MIN_SPLINE_CORRIDOR_JUNCTION_CLIP_DISTANCE = 0.05;
+export const MAX_SPLINE_CORRIDOR_JUNCTION_CLIP_DISTANCE = 500;
+export const SPLINE_CORRIDOR_JUNCTION_TERRAIN_MODES = [
+  "none",
+  "paintOnly",
+  "flattenAndPaint"
+] as const satisfies readonly SplineCorridorJunctionTerrainMode[];
+
+function cloneVec3(vector: Vec3): Vec3 {
+  return {
+    x: vector.x,
+    y: vector.y,
+    z: vector.z
+  };
+}
+
+function normalizePositiveFiniteNumber(
+  value: number,
+  min: number,
+  max: number,
+  label: string
+): number {
+  if (!Number.isFinite(value)) {
+    throw new Error(`${label} must be finite.`);
+  }
+
+  if (value < min || value > max) {
+    throw new Error(`${label} must be from ${min} to ${max}.`);
+  }
+
+  return value;
+}
+
+export function isSplineCorridorJunctionTerrainMode(
+  value: unknown
+): value is SplineCorridorJunctionTerrainMode {
+  return SPLINE_CORRIDOR_JUNCTION_TERRAIN_MODES.includes(
+    value as SplineCorridorJunctionTerrainMode
+  );
+}
+
+export function normalizeSplineCorridorJunctionRadius(value: number): number {
+  return normalizePositiveFiniteNumber(
+    value,
+    MIN_SPLINE_CORRIDOR_JUNCTION_RADIUS,
+    MAX_SPLINE_CORRIDOR_JUNCTION_RADIUS,
+    "Spline corridor junction radius"
+  );
+}
+
+export function normalizeSplineCorridorJunctionClipDistance(
+  value: number
+): number {
+  return normalizePositiveFiniteNumber(
+    value,
+    MIN_SPLINE_CORRIDOR_JUNCTION_CLIP_DISTANCE,
+    MAX_SPLINE_CORRIDOR_JUNCTION_CLIP_DISTANCE,
+    "Spline corridor junction clip distance"
+  );
+}
+
+export function normalizeSplineCorridorJunctionMaterialId(
+  value: string | null | undefined
+): string | null {
+  if (value === undefined || value === null || value.trim().length === 0) {
+    return null;
+  }
+
+  return value;
+}
+
+export function normalizeSplineCorridorJunctionName(
+  value: string | undefined
+): string | undefined {
+  if (value === undefined) {
+    return undefined;
+  }
+
+  const trimmed = value.trim();
+
+  return trimmed.length === 0 ? undefined : trimmed;
+}
+
+export function normalizeSplineCorridorJunctionTerrainMode(
+  value: unknown
+): SplineCorridorJunctionTerrainMode {
+  if (isSplineCorridorJunctionTerrainMode(value)) {
+    return value;
+  }
+
+  throw new Error(
+    "Spline corridor junction terrain mode must be none, paintOnly, or flattenAndPaint."
+  );
+}
+
+export function createSplineCorridorJunctionConnection(
+  overrides: Partial<SplineCorridorJunctionConnection> & {
+    pathId: string;
+  }
+): SplineCorridorJunctionConnection {
+  if (overrides.pathId.trim().length === 0) {
+    throw new Error("Spline corridor junction connection path id is required.");
+  }
+
+  return {
+    id: overrides.id ?? createOpaqueId("spline_junction_connection"),
+    pathId: overrides.pathId,
+    progress:
+      overrides.progress === undefined
+        ? 0
+        : Math.min(1, Math.max(0, overrides.progress)),
+    clipDistance: normalizeSplineCorridorJunctionClipDistance(
+      overrides.clipDistance ?? DEFAULT_SPLINE_CORRIDOR_JUNCTION_CLIP_DISTANCE
+    )
+  };
+}
+
+export function createSplineCorridorJunction(
+  overrides: Partial<
+    Omit<SplineCorridorJunction, "kind" | "connections">
+  > & {
+    connections: Array<
+      Partial<SplineCorridorJunctionConnection> & { pathId: string }
+    >;
+  }
+): SplineCorridorJunction {
+  if (overrides.connections.length < 2) {
+    throw new Error("Spline corridor junctions require at least two connections.");
+  }
+
+  return {
+    id: overrides.id ?? createOpaqueId("spline_junction"),
+    kind: "splineCorridorJunction",
+    name: normalizeSplineCorridorJunctionName(overrides.name),
+    visible: overrides.visible ?? DEFAULT_SPLINE_CORRIDOR_JUNCTION_VISIBLE,
+    enabled: overrides.enabled ?? DEFAULT_SPLINE_CORRIDOR_JUNCTION_ENABLED,
+    center:
+      overrides.center === undefined
+        ? { x: 0, y: 0, z: 0 }
+        : cloneVec3(overrides.center),
+    radius: normalizeSplineCorridorJunctionRadius(
+      overrides.radius ?? DEFAULT_SPLINE_CORRIDOR_JUNCTION_RADIUS
+    ),
+    materialId: normalizeSplineCorridorJunctionMaterialId(
+      overrides.materialId ?? DEFAULT_SPLINE_CORRIDOR_JUNCTION_MATERIAL_ID
+    ),
+    terrainMode:
+      overrides.terrainMode === undefined
+        ? DEFAULT_SPLINE_CORRIDOR_JUNCTION_TERRAIN_MODE
+        : normalizeSplineCorridorJunctionTerrainMode(overrides.terrainMode),
+    connections: overrides.connections.map(
+      createSplineCorridorJunctionConnection
+    )
+  };
+}
+
+export function cloneSplineCorridorJunction(
+  junction: SplineCorridorJunction
+): SplineCorridorJunction {
+  return createSplineCorridorJunction(junction);
+}
+
+export function getSplineCorridorJunctions(
+  junctions: SplineCorridorJunctionRegistry
+): SplineCorridorJunction[] {
+  return Object.values(junctions).sort((left, right) =>
+    (left.name ?? left.id).localeCompare(right.name ?? right.id)
+  );
+}
+