COM624P in 2026: running the free FHWA pile program today

Short answer: COM624P is the public-domain Federal Highway Administration (FHWA) program for laterally loaded piles. Wang & Reese documented version 2.0 in FHWA-SA-91-048 in the National Transportation Library. The manual remains available, but FHWA no longer distributes the DOS executable. Running the original now requires an emulator; modern options implement the same p-y method in maintained desktop or browser software.

If you searched for "COM624P download," you're probably after one of two things: a free, defensible way to run a p-y analysis, or the program your DOT design manual or an older report actually references. Both are reasonable. This post covers what COM624P is, why it still matters, what it actually takes to run it in 2026, and what has replaced it.

What COM624P is

Through the 1970s and 80s, Lymon C. Reese and his colleagues at the University of Texas at Austin turned full-scale lateral load tests into the p-y method: model the pile as a beam-column and the soil as a set of nonlinear springs, each defined by a p-y curve derived from instrumented field tests. The mainframe program that implemented it, COM624, was distributed to practice through the FHWA. COM624P is its microcomputer descendant — a FORTRAN program for MS-DOS, published with a full user's manual as FHWA-SA-91-048 (Wang & Reese, 1993). Version 2.0 added p-y curves for rock, analysis of piles in sloping ground, an improved multi-layer solution, and a wider menu of pile-head boundary conditions.

Because it was developed under federal contract, COM624P is public domain. No license, no fee, no restrictions. That single fact explains most of the searches this page answers.

Use the archived COM624P version 2.0 manual as the primary source for the input records, governing equations, soil models, boundary conditions, worked examples, and output definitions. The FHWA GEC 9 lateral-foundation manual gives the agency's later design guidance for p-y analysis and pile-group effects.

The governing equation

COM624P solves the beam-column-on-nonlinear-foundation problem: a pile of stiffness EI under axial load Pₓ and distributed load W, supported by soil whose resistance p depends nonlinearly on the local deflection y:

EI·y⁗ + Pₓ·y″ + Eₚᵧ·y − W = 0

Here Eₚᵧ = p/y is the secant modulus of the p-y curve at each depth. The equation is discretized by finite differences along the pile and solved iteratively — assume a deflected shape, evaluate the secant moduli from the p-y curves, re-solve, repeat until the deflections converge. The p-y families COM624P shipped with are the ones the profession still uses: Matlock (1970) soft clay, Welch & Reese (1972) stiff clay without free water, Reese, Cox & Koop (1975) stiff clay below the water table, Reese, Cox & Koop (1974) sand, and (from v2.0) rock. The full derivation and each curve family are written up on our method page.

COM624P inputs and outputs in a modern workflow

The file format changed, but the engineering model did not. This crosswalk shows where the original program's main records appear in PileCalc:

Why people still search for it

• It's free and public domain — the only zero-cost tool in a market where the commercial options run $950–$2,300.
• It's validated and citable. The FHWA manual documents the theory, the curves, and worked examples. Decades of designs were checked against it.
• It's referenced by name in older state DOT design manuals, geotechnical reports, and specifications — sometimes a reviewer literally asks for a "COM624 analysis."

The good news: a "COM624 analysis" is a method, not a binary. Any correct implementation of the equation and p-y curves above satisfies the intent — which is exactly what LPILE, RSPile, and PileCalc are.

The practical problems in 2026

Actually running the original program today is an exercise in retrocomputing:

• No official download. FHWA no longer distributes the executable. The user's manual survives in the National Transportation Library (ROSA-P), and copies of the program circulate on university and archive sites — but there is no authoritative source, which matters if your QA system asks where your software came from.
• It's a DOS program. The 16-bit executable won't run natively on 64-bit Windows or on macOS at all. You need DOSBox or a similar emulator, configured by hand.
• The input is unforgiving. Data goes in as structured text files with the conventions of its era; the built-in menu preprocessor helps, but a mistyped field produces wrong numbers or a crash, not a validation message.
• No support, no updates, no fixes. The last release predates most of the p-y research of the past three decades — no API sand formulation, no liquefied-sand models, no modern rock criteria beyond its original curves.
• Text-only output. Plotting deflection and moment diagrams means parsing fixed-width tables into a spreadsheet yourself.

The family tree: COM624 → COM624P → LPILE

Ensoft, Inc. — founded by Reese — took the same method commercial as LPILE, which has been actively developed ever since: a Windows interface, an expanded p-y library, LRFD load combinations, and nonlinear pile sections. LPILE is best understood as COM624P's maintained successor, and it's priced accordingly (currently $1,200 for a single seat plus $180/year maintenance — full breakdown in how much does LPILE cost). Rocscience's RSPile is an independent implementation of the same theory, validated against LPILE. PileCalc is another independent implementation — the same governing equation and p-y families, running in the browser.

Your options today

On the open-source row: several community efforts implement parts of the p-y method in Python or spreadsheets. Some are well built, but coverage of the curve families and — more importantly — published validation against LPILE-class references is inconsistent. If you go that route, plan to benchmark it yourself before it touches a deliverable.

COM624P in the browser

PileCalc is, at its core, a COM624P implementation: the same fourth-order governing equation, discretized by finite differences and solved by iteration on the secant soil modulus, with the same p-y families — Matlock soft clay, Welch & Reese and Reese-Cox-Koop stiff clay, Reese sand, plus the API/O'Neill-Murchison sand and Reese (1997) weak-rock models that postdate the original program, and user-defined curves. Where COM624P gave you fixed-width text, PileCalc gives you interactive deflection, moment, and shear diagrams with every node exportable.

And unlike a binary of uncertain provenance running in an emulator, the implementation is checked against published references and the results are public: API sand head deflection of 7.33 mm vs the 7.3 mm reference, Welch–Reese stiff clay 0.87 mm vs 0.85 mm, and a layered soil-movement case at 41.1 mm matching LPILE's chart value of ≈ 41 mm — the full suite is at docs/validation, with the underlying theory on the method page.

Common questions

Is COM624P still available for download?

Not from FHWA — the agency no longer distributes the program. The user's manual (FHWA-SA-91-048, Wang & Reese 1993) remains freely available through the National Transportation Library, and unofficial copies of the executable circulate on university and archive sites, but there is no authoritative download source as of mid-2026.

Is COM624P the same as LPILE?

They share the same method and lineage. COM624P is the public-domain FHWA program from 1993; LPILE is Ensoft's commercial successor, developed continuously since, with an expanded p-y library and a Windows interface. For the soil models both contain, a correct run of either should produce essentially the same deflections and moments.

Can I run COM624P on Windows 11 or a Mac?

Not natively — it's a 16-bit DOS program. You need an emulator such as DOSBox on either platform, plus a copy of the executable from an unofficial source. It works, but input is fixed-format text and output is text tables, so most engineers find a modern implementation of the same method faster to trust and to use.

Is there a free modern alternative to COM624P?

Yes. PileCalc's free tier runs the same governing equation and p-y curve families in the browser, with validation against LPILE and RSPile references published openly. Various open-source Python implementations also exist, with varying coverage — verify any of them against a known benchmark before relying on the results.

Curious what the p-y curves themselves look like for your soil? The free p-y curve generator builds Matlock, Reese, and API curves from your parameters — the same curves COM624P would have generated, without the emulator.