The municipality of Amsterdam wants to have an emission free taxi sector by 2025. In order to reach that goal, the city has taken a number of measures which favour clean taxis above conventional taxis. One of these measures is an innovative priority privilege scheme at the Amsterdam Central Station taxi stand, which should lead to shorter waiting times and more trips for clean taxis. The municipality wants to know if the measure is effective. In this study, we present an analysis of visiting behaviour of clean and regular (diesel) taxis in order to assess the effectiveness of the privilege scheme to attract more clean taxis. As such it aims to contribute to a better understanding of the effect of the priority measure at the Amsterdam Central Station and to provide input for policy makers to introduce incentive schemes to stimulate clean taxis in cities. Analysed data covers a timespan from one year, starting October 2015 when the privilege scheme started with a call rate of 1 clean taxi to each 4 taxis called for a ride. The analysis shows the number of arriving clean taxis to shift from 1:6 to 1:4 during the observation period. Based on this analysis the municipality decided to modify the preference ratio beginning 2017. This study contributes to a better understanding of the effect of the privilege measures and provides input for policy makers introducing incentives to stimulate clean taxis in cities.