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Emission Test Cycles

Standard Road Cycle (SRC) and Standard Bench Cycle (SBC)

SRC cycle description | SBC cycle description

The Standard Road Cycle (SRC) and Standard Bench Cycle (SBC) were introduced by the US EPA in 2005 for predicting the useful life emissions of new light-duty vehicles under the CAP 2000 program. The CAP 2000 durability provisions and the SRC/SBC tests are applicable mostly to gasoline cars with three-way catalysts.

SRC. The Standard Road Cycle is a whole vehicle aging cycle. Manufacturers can demonstrate the emission levels of new vehicles at the end of their useful life period by running a vehicle on the SRC cycle for the full useful life mileage of the vehicle (e.g., 120,000 miles for Tier 2 light-duty vehicles).


Figure 1. Standard Road Cycle

The SRC, shown in Figure 1, consists of seven laps of 3.7 miles each. The average speed on the SRC is 46.3 mph, the maximum cruise speed is 75 mph, and the acceleration rates range from light to hard accelerations. Most accelerations are moderate and there are no wide-open-throttle accelerations. The SRC contains 24 fuel-cut decelerations. The deceleration rates range from coast-down (no brake force applied) to moderate.

SBC. In lieu of running the SRC test over the full useful life mileage, manufacturers can perform accelerated aging on an engine test bench. The aging is performed by repeated runs of the Standard Bench Cycle for a required period of time. The SBC time period is determined by a complex calculation based on the catalyst temperature profile measured during the SRC cycle.


Figure 2. Standard Bench Cycle

The SBC, Figure 2, is a 60-second cycle defined based on the catalyst temperature, engine air/fuel (A/F) ratio, and the amount of secondary air injection which is added in front of the catalyst (using shop air). The catalyst bed temperature is controlled at 800°C during the “stoichiometric” condition, and at 890°C during the “rich” condition.