A basic freeway segment is defined as a section of a divided roadway having two or more lanes in each direction, full access control, and traffic that is unaffected by merging or diverging movements near ramps. It is important to note that capacity analysis for divided roadways focuses on the traffic flow in one direction only. This is reasonable because the objective is to measure the highest level of congestion. Due to directional imbalance of traffic flows — for example, morning rush hours having
higher volumes going toward the central city and evening rush hours having higher volumes going away from the central city — consideration of traffic volumes in both directions is likely to seriously understate the true level of traffic congestion.
The base conditions for a basic freeway segment are defined as :
• 12-ft minimum lane widths
• 6-ft minimum right-shoulder clearance between the edge of the travel lane and objects (utility poles, retaining walls, etc.) that influence driver behavior
• 2-ft minimum median lateral clearance
• Only passenger cars in the traffic stream
• Five or more lanes in each travel direction (urban areas only)
• 2-mi or greater interchange spacing
• Level terrain (no grades greater than 2%)
• A driver population of mostly familiar roadway users