In traffic flow, what is the maximum number of cars on a road section where all cars are stopped?

The maximum number of cars on a road section where all cars are stopped is determined by a fundamental traffic flow concept called jam density. Jam density, also known as saturation density or maximum density, represents the highest possible concentration of vehicles on a roadway, occurring when all vehicles are stationary, either bumper-to-bumper or at their absolute minimum safe and practical spacing. This state signifies that no more vehicles can physically fit onto that section of road. Each stopped vehicle, including the minimal space it occupies front and back from the adjacent vehicles, effectively takes up a specific length of the road. This effective length per vehicle is the sum of the average physical length of a vehicle and the average minimum bumper-to-bumper gap between stopped vehicles. For typical passenger cars, the average length is approximately 4 to 5 meters (13 to 16.5 feet), and the minimum stopped gap is generally about 0.5 to 1.5 meters (1.6 to 5 feet). Therefore, each stopped car occupies an effective road length of roughly 4.5 to 6.5 meters (14.6 to 21.5 feet). To calculate the maximum number of cars for a given road section, you divide the total length of the road section by this average effective length per stopped car. For example, on a 1-kilometer (1000-meter) road section, if each car effectively occupies 6 meters, then approximately 166 cars (1000 meters / 6 meters per car) can be accommodated when all are stopped. This means jam density typically ranges from about 150 to 220 vehicles per lane-kilometer (or 240 to 350 vehicles per lane-mile).