In this paper we deal with traffic behaviours on a section of highway including an on-ramp by means of queuing theory. It is the purpose of this paper to provide the adequate capacity for highway on-ramps, which is useful for the design of on-ramps and the traffic control of highway. The highway on-ramp merging is modeled as a queue
and the system is solved. Then the maximum possible flows for merging from an on-ramp is obtained in a form of an function of through lane flows. The traffic capacity of an on-ramp is estimated from the relation between the average waiting time before merging and the incoming flow from an on-ramp, which is induced by the theory of queues.