Santa Barbara County ambulance dispatch data from 2006 was analyzed to determine the effect on performance due to system load. A variable called 'neighbors' (η) was calculated as a measure of location specific system load, where η is the number of ambulances that were dispatched within the previous hour within a fixed distance of 20 kilometers. It was determined that calls for which there are neighbors have a statistically higher proportion of response time violations than calls for which there are no neighbors. It was found that on average, the odds ratio of the probability of a response time violation increases by 19.1% for each additional neighbor. However the fact that system load degrades system performance may not itself be very helpful. It was determined that the effect due to system load is not homogeneous in space. The inhomogeneous K-function for locations of calls where neighbors corresponded with a response time violations indicated that there is more clustering compared to inhibition than expected under the hypothesis that these points were drawn without bias from the overall spatial call conditional intensity. This paper identifies regions where system load most impacts ambulance response performance.