Traffic congestion is one of the most serious problems facing by not only the developed countries, but also by developing countries, including Cambodia. Efforts have been made to minimize urban traffic congestion in order to improve the traffic flow. This paper intends to provide the best alternative solutions to improve traffic flow at a busy intersection in Phnom Penh, Cambodia—i.e., Neakvoan intersection. Three alternative solutions were proposed based on redesign of road geometry and reconfiguration of one- way traffic road, and analyzed queue length and delay via a micro-simulation environment (i.e., PTV VISSIM) using actual data from traffic count survey. Results showed that, compared with the existing conditions, the third alternative solution performed better than other alternatives, by improving the traffic flow at Neakvoan intersection up to 39% with a reasonable level of service D. The proposed alternative solution was evaluated and accepted for implementation by the government.