In the free market, as motorists will only take into consideration of their private benefits, they will consume at the level where private benefit, which is also the social benefit equals to the private cost as shown in the diagram above at equilibrium E0 with P0 and Q0. However, the economically efficient level is at E1 where social cost equals to social benefit. Thus, there is a need for the government to impose the congestion tax to bring the Equilibrium back to its socially optimum level. The government should impose the congestion tax at P1 and must be equal to the external cost of driving on road. This amount of tax imposed at P1 will internalise the external cost and close the divergence between S1 and S2. As a result, the supply curve will shift from S1 to S2 and the market equilibrium will move from E0 to E1 where the quantity of car trips is now
References: 1. Goh, M. (2002). Congestion management and electronic road pricing in Singapore. Journal of Transport Geography, 10, 29–38. 2. Stanley, J (2011). “The case for congestion charging in Australia”, The Conversation (31 March, 2011). 3. Laura Blow, Andrew Leicester, Zoë Smith, London’s Congestion Charge. Available from <eprints.ucl.ac.uk/14932/1/14932.pdf> [ February 2003] 4. Transport For London, Transport for London Central Condon Congestion Charging, Available from: <www.tfl.gov.uk/assets/downloads/fifth-annual-impacts-monitoring-report-2007-07-07.pdf> [July 2007] 5. Hubbard, Garnett, Lewis, O’Brien, 2012, Microeconomics, Pearson, Australia. 6. Land Transport Authority, Certificate of entitlement (COE), Available from: <www.lta.gov.sg/content/ltaweb/en/roads-and-motoring/owning-a-vehicle/vehicle-quota-system/certificate-of-entitlement-coe.html> [ April 2013] 7. Car Prices Information. Available from: <http://www.carsguide.com.au> [1 April 2013]