Theoretical sustainable flow
Per lane: Standard traffic lanes handle a maximum sustainable flow of about 1,800 to 2,100 vehicles per hour per lane under ideal conditions before breaking down into unstable queues and congestion.
The maximum flow of a 30mph A road is typically about 1,500 to 1,800 vehicles per hour per lane under ideal conditions, based on the Traffic Capacity of Urban Roads standards. Key factors affecting this rate are lane width, junction frequency, and pedestrian activity.