One point to consider is that the system of emergency management are coming to a tipping point as more professionals realize that in a number of disasters and specific locations large scale evacuation is simply not practical.

Look for a slow shift toward an increasing number of plans to resort to 'sheltering in place'; targeted local evacuations, hardening of homes, and shelters, both purpose built and within select buildings (reminiscent of the old CD fallout shelter program) as a coping strategy.

The shift may not be easily seen as evacuation is still part of it. The general plan may be to evacuate the smallest practical area of direct impact. In a wider zone critical need cases and the sick and infirm would be evacuated while the remainder of the population use some combination of hardening their homes and laying in supplies or shifting to local shelters if their residences are unsuitable.

If and when the situation develops and more people need to be moved out of danger then your dealing with people who are forewarned, prepared, mobile and relatively healthy.