A method called “shoulder pricing” is used, which involves increasing the rate in steps every half an hour before the peak and decreasing it after the peak. Charges are relatively low: the maximum rate for cars is SGP 3 and SGP 2.50 to enter the central business district, but the traffic flow has appeared to be quite sensitive to the charge: short-term elasticities have been estimated to be in a range between 0 and -0.42 (Menon and Shin, 2004). The immediate effect of the introduction of ALS in 1975 was the reduction of car traffic entering the city centre during the morning peak hours by over 70%.