A regulation was implemented on 9/1/2009, excluding Euro 0, I and II heavy duty vehicles from entering Amsterdam's Low Emission Zone (LEZA). The current study investigated whether and to what extent this regulation had an effect on air quality. Data for a period starting two years before the regulation up to 31 December 2010 were obtained from two monitoring sites within the LEZA, one located in a street frequently used by heavy-duty vehicles, and one at an urban background location. The difference in concentrations of NO2, NOx, PM10 and soot, between the two sites was attributed to traffic. Soot was measured by two proxies, Elemental Carbon (EC) and Absorbance that showed a significant mutual correlation. The traffic contribution concentrations measured were adjusted for wind direction, wind speed, type of day (weekday/weekend) and traffic intensity. Since the implementation of the LEZA, the traffic contribution concentrations compared to the roadside site concentrations were decreased by 4.9% (95%-CI: 3.0–6.9%) for NO2, 5.9% (95%-CI: 3.7–6.4%) for NOx, 5.8% (95%-CI: 3.3–8.4%) for PM10, 7.7% (95%-CI: 2.3–13.0%) for Absorbance and 12.9% (95%-CI: 5.2–20.5%) for EC. The current study demonstrated significant decreases in traffic-related air pollution concentrations in the vicinity of a roadside monitoring station after the implementation of a low emission zone in Amsterdam.