An ETA That Forgot the Sailing

Container free time, demurrage, billing deadlines, bill of lading dates and EDI timestamps.

An ETA That Forgot the Sailing

Shanghai to Chicago: 6 hours by truck, 2 days at the terminal, 14 days 6 hours at sea, 36 hours at Los Angeles, 52 hours by rail. The ship sails at 10:00 Shanghai time on 13 June.

The naive approach

// The naive approach: add every duration and every dwell to the first departure
const hours = 6 + 48 + 342 + 36 + 52; // 484
new Date(Date.parse("2024-06-10T00:00:00Z") + hours * 3600e3).toISOString();
// "2024-06-30T04:00:00.000Z" — 20 hours early: the ship did not leave when the dwell ended

Watch it break

The naive approach silently produces wrong results — there is no GMT equivalent to demonstrate because the failure is not using GMT.

Why

The sum assumes every leg leaves the moment the handoff's dwell ends. A ship leaves on its schedule, so the cargo that cleared the terminal at 14:00 on the 12th waits until 10:00 on the 13th. One total also hides where the time went: the 484 hours mix time at sea, which the carrier's schedule forecasts, with time at terminals, which congestion moves. `multimodalETA` schedules the legs with `scheduleDelivery`, so a scheduled departure is honoured and one inside the dwell is a missed connection (`null`). It then reports `totalTransit`, the legs' durations, and `totalDwell`, the time actually spent at the handoffs, wait included. The two add up to the elapsed time: 400 + 104 = 504 hours.

The gmt approach

import { multimodalETA } from "@northguild/gmt/intermodal";

multimodalETA([
{ departure: "2024-06-10T08:00:00+08:00[Asia/Shanghai]", duration: "PT6H",
  timeZone: "Asia/Shanghai", dwellAfter: "P2D", mode: "truck" },
{ departure: "2024-06-13T10:00:00+08:00[Asia/Shanghai]", duration: "P14DT6H",
  timeZone: "America/Los_Angeles", dwellAfter: "PT36H", mode: "ship" },
{ duration: "PT52H", timeZone: "America/Chicago", mode: "rail" },
]);
// { eta: "2024-06-30T19:00:00-05:00[America/Chicago]", totalLegs: 3,
//   totalTransit: "PT400H", totalDwell: "PT104H" }

Same widget, working

The widget above starts from the legs with no scheduled sailing: 400 hours moving and 84 at handoffs. Add departure: "2024-06-13T10:00:00+08:00[Asia/Shanghai]" to the ship leg and totalDwell grows to PT104H while totalTransit stays PT400H. Make it "2024-06-12T13:00:00+08:00[Asia/Shanghai]", inside the two-day dwell, and the result is null: a missed connection. The full rules are in Intermodal: B/L Dates and Multimodal ETA.