Why are so many lines still reserved for emergency telephone calls in emergency situations?

We propose a threshold relaxation and holding time limitation for general telephone calls under trunk reservation control in emergency situations. This TR-HTL method aims to accept more general calls while required emergency calls are still accepted. Computer simulation with a queueing system model of a telephone exchange showed that the threshold relaxation increased the number of accepted general calls while still enabling the required number of emergency calls to be accepted. Comparison between two strategies to set the holding time limit of general calls showed that the value of the limit and the call-blocking rate are in a strong trade-off relationship when the limit is short. An investigation of the relationships between the threshold relaxation rate and the call-blocking rate showed that reserving just 5% of the estimated traffic intensity of emergency calls enabled the required number of emergency calls to be accepted, increasing the number of accepted general calls. Moreover, we showed that much fewer reserved lines are needed for guaranteeing emergency calls.