Intermodal Drayage Billing: Split Chassis & Private Equipment Per Diem Solvers

The Persistent Billing Friction in Marine Terminal Drayage

Intermodal drayage operators face one of the most complex billing environments in freight transportation. When a loaded import container is delivered to a consignee and the empty unit must be returned, the physical movement of equipment often diverges from the contractual billing paths. This divergence is most pronounced during chassis splits.

A chassis split occurs when the empty ocean container is returned to a marine terminal gate while the chassis on which it was transported must be returned to an off-dock chassis pool depot operated by a different entity. The ocean carrier (steamship line) controls the container per diem and detention clock. A separate equipment provider or chassis pool manager controls the chassis per diem and any associated accessorial charges. These two clocks are contractually and operationally independent, yet they share the same physical movement until the moment the container is detached from the chassis at the terminal.

When interchange timestamps are not captured and reconciled with precision, motor carriers and 3PLs receive dual invoices that appear to overlap. The ocean carrier may assess detention for late container return while the chassis pool simultaneously bills per diem for delayed chassis return. These charges are frequently issued on separate invoices arriving weeks apart, making manual reconciliation labor-intensive and error-prone.

Technical Anatomy of a Chassis Split Event

From a systems architecture perspective, each chassis split generates at least four distinct timestamped events that must be stored independently:

• Street pickup of loaded container and chassis (origin interchange)
• Delivery of loaded container to consignee (street-turn or empty pull authorization)
• Return of empty container to marine terminal gate (TIR receipt timestamp)
• Return of empty chassis to designated pool depot (chassis interchange timestamp)

Enterprise TMS platforms must maintain a normalized relational model that decouples container and chassis lifecycles while preserving their temporary pairing. A typical schema fragment includes:

CREATE TABLE equipment_pairing (
    pairing_id BIGINT PRIMARY KEY,
    container_number VARCHAR(20) NOT NULL,
    chassis_number VARCHAR(20),
    chassis_provider_id INT,
    pickup_timestamp TIMESTAMPTZ,
    delivery_timestamp TIMESTAMPTZ,
    empty_return_container_timestamp TIMESTAMPTZ,
    empty_return_chassis_timestamp TIMESTAMPTZ,
    terminal_facility_id INT,
    chassis_pool_facility_id INT,
    street_turn_flag BOOLEAN DEFAULT FALSE,
    created_by_system VARCHAR(50)
);

This structure allows the TMS to calculate per diem windows independently for the container (governed by the ocean carrier tariff) and the chassis (governed by the pool agreement). When the empty_return_container_timestamp and empty_return_chassis_timestamp differ by more than the allowed free time plus transit buffer, automated alerts are generated.

Ocean Carrier Detention vs. Chassis Pool Per Diem: Contractual Conflicts

Ocean carriers publish detention and demurrage tariffs that begin when the container leaves the terminal and end when it is returned in acceptable condition. Many tariffs now include "container return" language that references only the physical return of the box, regardless of chassis status. Conversely, chassis pool agreements typically charge per diem from the moment the chassis is taken from the pool until it is returned empty and clean.

When a drayage carrier uses private chassis instead of pool equipment, the complexity increases. Private chassis must still satisfy the ocean carrier's equipment interchange agreement (EIR) at the marine terminal. The ocean carrier may still assess detention on the container while the private chassis owner separately invoices the motor carrier for equipment use. These dual streams must be audited against the same set of gate transactions.

Common failure modes include:

• Terminal gate systems recording only the container return TIR without capturing chassis return details
• Chassis pool depots recording return times that differ by hours from terminal timestamps due to yard congestion or after-hours drop
• Street-turn exceptions where the empty container is immediately reloaded without a formal terminal return, breaking the expected timestamp sequence

Building an Automated Per Diem Solver in Enterprise TMS

Strong Tower Consulting designs and implements per diem solvers as part of broader TMS implementation projects. The solver engine operates on three core data feeds:

1. EDI 322 terminal gate activity reports (including TIR receipts)
2. Chassis pool provider API or EDI 214 status updates
3. Internal driver ELD and mobile app timestamps captured at hook/unhook events

The solver maintains a rules engine that encodes each ocean carrier's detention policy and each chassis pool's per diem schedule. Rules are stored in a declarative JSON policy table that can be updated without code changes. When a mismatch is detected, the system assembles a dispute package containing:

• Paired container and chassis movement history
• Gate receipt images and TIR numbers
• Calculated free time windows per contract
• Supporting EDI transaction logs
• Recommended adjustment amount and reference invoice numbers

This package is transmitted via EDI 210 credit memo, API, or email portal depending on the counterparty's preferred method. Integration with transportation accounting systems ensures that approved credits automatically update AP ledgers and prevent duplicate payments.

Independent Container-to-Chassis Pairing and Timestamp Reconciliation

Modern intermodal TMS platforms treat container and chassis as peer entities that may be transiently linked. The pairing table records both the business pairing (who authorized the move) and the physical pairing (confirmed at hook and unhook via driver mobile application or yard sensor). This dual confirmation reduces reliance on terminal-provided data alone.

When a chassis split is identified (different return facilities for container and chassis), the system automatically flags the record and begins parallel per diem clocks. Street-turn exceptions are handled by a dedicated validation workflow that cross-references the load tender, the delivery confirmation, and the subsequent reload authorization to avoid erroneous "empty return" timestamps.

Integration with ELD and EDI systems provides the granular GPS and timestamp data required to defend against wrongful assessments. When an ocean carrier or chassis provider disputes the carrier's records, the TMS can produce a complete audit trail showing every status change with source system and user attribution.

Dual Invoice Auditing and Workflow Automation

Because ocean carriers and chassis providers invoice separately and on different cycles, automated invoice ingestion becomes essential. The TMS ingests both paper and electronic invoices, normalizes them to a common schema, and matches them against the equipment pairing records.

Discrepancies above a configurable threshold trigger an exception workflow routed to the billing analyst. The per diem solver pre-populates the dispute with all necessary documentation, reducing research time from hours to minutes. Approved disputes are tracked through resolution and automatically reconciled in the accounting system.

For carriers operating across multiple ports, the system maintains a master tariff library that normalizes terminology across steamship lines. What one carrier calls "per diem" another may call "equipment detention." The solver abstracts these differences so operational users see consistent business rules.

Implementation Best Practices for Intermodal Drayage Operators

Organizations seeking to reduce per diem leakage should prioritize the following technical capabilities when evaluating or upgrading their TMS:

• Normalized equipment master with independent container and chassis lifecycles
• Real-time pairing capture at the driver level via mobile applications
• Automated ingestion and parsing of terminal gate EDI 322 and TIR data
• Declarative rules engine for per diem, detention, and chassis pool tariffs
• Automated dispute package generation with supporting documentation
• Seamless integration to accounting platforms for credit memo processing

Strong Tower Consulting works with both asset-based drayage carriers and brokerage-3PL operations to implement these capabilities. Our business process optimization methodology ensures that technical solutions align with actual yard, dispatch, and billing workflows rather than forcing operations to conform to rigid software assumptions.

Carriers focused on intermodal drayage, brokerage and 3PL, or truckload operations benefit from purpose-built solvers that eliminate the manual spreadsheet reconciliation that still dominates many mid-size fleets.

Conclusion: From Reactive Dispute Management to Proactive Prevention

The financial impact of unresolved chassis split per diem and detention charges can reach tens of thousands of dollars per month for active intermodal drayage operations. By implementing an automated per diem solver that independently tracks container and chassis timestamps, reconciles gate receipts, and generates dispute documentation, carriers replace reactive firefighting with systematic prevention.

Strong Tower Consulting, LLC and Exspeedite LLC are separately organized sister companies under common ownership (separate EINs; liability firewall). Scott Elliott is founder and transportation systems architect of both. Our work with motor carriers and freight brokers since 2008 has repeatedly demonstrated that precise equipment lifecycle management is one of the highest-ROI technology investments available to intermodal operators.

To evaluate how your current TMS and operational processes handle chassis splits and per diem reconciliation, we invite you to schedule a no-obligation assessment.