Real-world design speeds are often based on what percentile of speed?

The 85th percentile speed is a commonly used benchmark in traffic engineering for determining design speeds because it reflects the speed at which 85% of vehicles are observed to be traveling at or below under free-flowing conditions. This approach is grounded in the principle that drivers tend to travel at speeds that feel safe and comfortable given the road conditions. By focusing on the 85th percentile, engineers ensure that the design accommodates the majority of drivers while still providing a reasonable safety margin. It helps to minimize the risk of accidents that may arise from excessively high speeds, while also considering the prevailing behavior of drivers in that environment. Thus, using the 85th percentile speed as a standard aids in creating road designs that enhance safety and efficiency for all users.