A two lane urban road with one way traffic has a maximum capacity of 1800 vehicles/hour. Under the jam condition, the average length occupied by the vehicles is 5.0 m. The speed versus density relationship is linear. For a traffic volume of 1000 vehicles/hour, the density (in vehicles/km) is

For a linear speed-density relationship, the capacity occurs at half the jam density. Jam density (Kj) = 1000 / 5 = 200 vehicles/km. Capacity (q_max) = 1800 = (V_free * Kj) / 4, so V_free = 36 km/h. Using q = V * K and V = V_free * (1 - K/Kj), we get q = V_free * K * (1 - K/Kj). Solving 1000 = 36 * K * (1 - K/200) yields K = 58 vehicles/km.