Traffic problems in Bangkok have an influence on road users during peak hours. Especially, the traffic bottleneck on curves under the saturation flow situation must be remedied in order to increase the roadway capacity and speed. However, the appropriate speed for heavy vehicles is taken into consideration during off peak after the increasing lanes. This leads to the Rollover of heavy truck and rear-end collisions which are the main causes of vehicles accidents on curves. In addition, road accidents on curves account for the majority of all accidents in Thailand. According to the road accidents data collected in Thailand, 44 road deaths per 100,000 people, the country ranks second in the world for road accidents. When Thailand’s Code of Geometrical Design is compared with AASHTO (The American Association of State Highway and Transportation Officials), the super elevation length of Thailand’s Code is more than AASHTO. As a result, drivers are not made aware of the appropriate speed and the stooping sight distances (SSD) on curves. Therefore, the Design of Traffic Signage under the Perception and Reaction Times (PRT) for Thai Drivers will be taken into account.