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Exhaust emissions were evaluated for four different catalytic exhaust emission control systems. Each system utilized a diesel oxidation catalyst, a metal-substrate partial-flow diesel particulate filter, an iron-exchanged or copper-exchanged Y-zeolite catalyst for urea selective catalytic reduction, and an ammonia slip catalyst. A 5.9-liter diesel truck engine was modified to match the exhaust conditions of a four-stroke diesel locomotive engine meeting the current Tier 2 locomotive emissions standards. NOx emissions, CO₂ emissions and exhaust temperatures were matched to the eight locomotive "throttle notch" power settings while exhaust mass flow was maintained near a constant fraction of locomotive exhaust mass flow for each "throttle notch" position. Regulated and unregulated exhaust emissions were measured over a steady-state test cycle for each of the four systems at low hours and following accelerated thermal aging and accelerated oil ash accumulation.