This study, conducted by the Traffic Bureau of the Ohio State Highway Department, aims to determine the traffic capacity of two-lane roadways. The research, supervised by H.E. Neal and J.J. Darnall, utilized a photographic method to collect data on vehicle speeds and densities. Key findings include: 1. **Average Free Moving Speed**: On both two and three-lane roads, the average free-moving speed is approximately 43 miles per hour. 2. **Effect of Congestion**: When the number of vehicles exceeds 400 to 600 per hour, the average speed decreases significantly, with slow-moving vehicles having a more pronounced effect. 3. **Vehicle Speeds**: Light trucks (850 vehicles) averaged 41.0 miles per hour, heavy trucks (225 vehicles) averaged 32.4 miles per hour, and buses averaged 41.6 miles per hour. 4. **Traffic Capacity**: The study determined that the working capacity of a two-lane roadway is about 400 to 600 vehicles per hour. Beyond this density, the average speed decreases, indicating congestion. 5. **Data Collection Method**: The data were collected using a 16mm movie camera that captured images at intervals of 88 minutes, allowing for the calculation of vehicle distances and speeds. 6. **Statistical Analysis**: The data were analyzed to determine the relationship between speed and density, with a linear relationship observed for speeds below the free speed. 7. **Conclusion**: The study concluded that the average free-moving speed on first-class roadways is nearly constant at 43 miles per hour, and that roughness has little effect on speed. The results provide valuable insights into traffic behavior and capacity on two-lane roadways. The discussion section highlights the methods used by other researchers to estimate traffic speeds and capacities, emphasizing the importance of accurate data collection and analysis in traffic management.This study, conducted by the Traffic Bureau of the Ohio State Highway Department, aims to determine the traffic capacity of two-lane roadways. The research, supervised by H.E. Neal and J.J. Darnall, utilized a photographic method to collect data on vehicle speeds and densities. Key findings include: 1. **Average Free Moving Speed**: On both two and three-lane roads, the average free-moving speed is approximately 43 miles per hour. 2. **Effect of Congestion**: When the number of vehicles exceeds 400 to 600 per hour, the average speed decreases significantly, with slow-moving vehicles having a more pronounced effect. 3. **Vehicle Speeds**: Light trucks (850 vehicles) averaged 41.0 miles per hour, heavy trucks (225 vehicles) averaged 32.4 miles per hour, and buses averaged 41.6 miles per hour. 4. **Traffic Capacity**: The study determined that the working capacity of a two-lane roadway is about 400 to 600 vehicles per hour. Beyond this density, the average speed decreases, indicating congestion. 5. **Data Collection Method**: The data were collected using a 16mm movie camera that captured images at intervals of 88 minutes, allowing for the calculation of vehicle distances and speeds. 6. **Statistical Analysis**: The data were analyzed to determine the relationship between speed and density, with a linear relationship observed for speeds below the free speed. 7. **Conclusion**: The study concluded that the average free-moving speed on first-class roadways is nearly constant at 43 miles per hour, and that roughness has little effect on speed. The results provide valuable insights into traffic behavior and capacity on two-lane roadways. The discussion section highlights the methods used by other researchers to estimate traffic speeds and capacities, emphasizing the importance of accurate data collection and analysis in traffic management.