We examine a model of traffic flow on a highway segment, where traffic can be impaired by random incidents (usually, collisions). Using analytical and numerical methods, we show the degree of sensitivity that the model exhibits to the distributions of service times (in the queueing model) and incident clearance times. Its sensitivity to the distribution of time until an incident is much less pronounced. Our analytical methods include an M/G t /∞ analysis (G t denotes a service process whose distribution changes with time) and a fluid approximation for an M/M/c queue with general distributions for the incident clearance times. Our numerical methods include M/PH 2 /c/K models with many servers and with phase-type distributions for the time until an incident occurs or is cleared. We also investigate different time scalings for the rate of incident occurrence and clearance.