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A drive cycle is a fixed speed-versus-time trace that a vehicle follows on a laboratory dynamometer so that emissions and fuel use can be compared between vehicles. The same phrase is also used for the mix of driving conditions that lets a car’s on-board diagnostic monitors finish running.
This guide is for researchers, test-lab staff and readers of vehicle test reports who need to know which meaning a document uses, what a named cycle represents, and what a cycle result does and does not say.
Short answer
In emissions testing, a drive cycle (EPA also says “drive schedule”) is a published second-by-second speed trace. A driver or robot follows it while the vehicle sits on a chassis dynamometer, so every laboratory applies the same demand. In vehicle maintenance and inspection, a “drive cycle” instead means a pattern of normal driving that allows on-board diagnostic (OBD) readiness monitors to complete.
Two meanings of “drive cycle”
| Aspect | Dynamometer test cycle | OBD readiness drive cycle |
|---|---|---|
| What it is | A standardized speed-time schedule run in a laboratory | A period of driving in varied conditions after codes are cleared or a repair is made |
| Who uses it | Certification and research test labs, regulators | Inspection and maintenance (I/M) programs, technicians, vehicle owners |
| Where it is defined | EPA dynamometer drive schedules; UN GTR No. 15 (WLTP) | Program rules; EPA best-practices material for I/M readiness |
| Output | Emissions, fuel or energy consumption for the cycle | Readiness monitors set to “ready” or “not ready” |
The rest of this page concentrates on the first meaning, then covers the second briefly.
How a dynamometer test cycle is used
The vehicle is held on rollers while a driver follows the speed trace. Because the trace is identical across laboratories, results are comparable between vehicles. For the global light-vehicle procedure, UN Global Technical Regulation No. 15 (the Worldwide Harmonized Light Vehicles Test Procedure, WLTP) prescribes a “driving cycle and associated test procedure for the common measurement of criteria compounds, CO2, fuel and energy consumption”. It was established in the UN Global Registry on 12 March 2014. The procedure also covers setting the dynamometer load from the vehicle’s road load, determined by coastdown or a torque meter, before the Type 1 test.
The GTR document states that the cycle was built from driving data collected from Contracting Parties and weighted by each region’s share of globally driven mileage. The data were cut into idling periods and “short trips”, and randomised combinations of those pieces generated draft cycles. The resulting Worldwide Harmonized Light Vehicles Test Cycle (WLTC) has Low, Medium, High and Extra High phases, with Classes 1, 2 and 3 that use class-dependent phases.
The GTR does not set emission limit values. Regional legislation does that, so a cycle is a measurement condition, not a regulation. For the pollutants and standards the cycles are used to measure, see vehicle emissions.
EPA schedules and what each represents
| Schedule | What EPA says it represents |
|---|---|
| UDDS (“LA4”) | City driving |
| FTP (“EPA75”) | The UDDS, a 10-minute soak, then the first 505 seconds of the UDDS again |
| HWFET | Highway driving under 60 mph |
| US06 | High-acceleration, aggressive driving (supplemental FTP) |
| SC03 | Driving with air conditioning operating (supplemental FTP) |
| NYC cycle | Low-speed, stop-and-go driving |
| LA-92 | Higher top and average speeds than the FTP, less idle, fewer stops per mile and higher maximum acceleration; the “Hot LA-92” is its first 1,435 seconds, used by CARB for emission inventory, and “LA-92 Short” is its first 969 seconds |
| IM240 | Used in inspection and maintenance programs; no longer required for EPA certification |
Source: US EPA, Dynamometer Drive Schedules, read 2026-11-08. EPA publishes each schedule as a downloadable speed-time file.
The OBD readiness drive cycle
On-board diagnostic systems run self-tests called readiness monitors. In an EPA best-practices document for inspecting diesel vehicles under 14,001 lb GVWR, EPA states that readiness depends on how the vehicle has been driven since fault codes were cleared. The document says a gasoline OBD system may typically run all monitors within two weeks, while a diesel system can take eight weeks or more, because some diesel monitors are linked to particulate-filter regeneration and several regeneration events may be needed. It recommends that operators drive for two or three weeks after codes are cleared before an inspection, rather than the one week often used for gasoline vehicles. EPA’s cover note says the document is a courtesy to states and is not official EPA guidance.
The same document describes using the distance travelled and the number of warm-ups since codes were cleared as inputs to the readiness decision.
Where it matters for labs and test programs
- Method statements. A reported emissions or consumption figure should name the cycle (for example FTP-75 or WLTC class and phase), because the cycles represent different driving conditions.
- Procedure control. Dynamometer load setting and cycle execution belong in a written standard operating procedure, and the dynamometer and its measurement equipment depend on calibration.
- Comparisons across regions. Results from different cycles, such as the EPA FTP and the WLTC, are not interchangeable because the cycles were built from different data and have different phase structures.
Common misunderstandings
- A cycle is a route. It is a speed-time trace, not a road or a map. The WLTC was constructed from short trips and idling periods, not recorded from one journey.
- The cycle sets the limit. GTR No. 15 expressly leaves limit values to regional legislation.
- One drive makes monitors ready. EPA’s diesel material describes weeks of normal driving, not a single trip.
Frequently asked questions
What is a drive cycle in emissions testing?
It is a standardized speed-versus-time schedule followed on a chassis dynamometer so emissions and fuel use can be compared between vehicles and laboratories.
What is the difference between FTP-75 and WLTC?
The FTP (“EPA75”) is built from the UDDS city schedule with a 10-minute soak and a repeat of its first 505 seconds. The WLTC comes from UN GTR No. 15 and has Low, Medium, High and Extra High phases across three classes, constructed from weighted international driving data.
Is IM240 still used for certification?
No. EPA says IM240 is used in inspection and maintenance programs and is no longer required for EPA certification.
What is an OBD drive cycle?
It is the pattern of driving that lets a vehicle’s diagnostic monitors run and set to ready after codes are cleared. EPA’s diesel I/M best-practices document recommends two or three weeks of driving for diesels before inspection.
Sources
- US EPA, Dynamometer Drive Schedules, read 2026-11-08.
- UNECE, Global Technical Regulation No. 15 (WLTP), ECE/TRANS/180/Add.15, established 12 March 2014, read 2026-11-08.
- US EPA, Best Practices for Addressing OBD Readiness in IM Testing of Diesel Vehicles Under 14,001 Pounds GVWR, read 2026-11-08.
