No city is. Evacuations take planning, discipline and enforcement.
Identifying those most at risk, finding bottlenecks, rationing throughput, deploying support to those at the end of the line and enforcing rules (as well as messaging such enforcement) are key.
For a hurricane hitting Houston, this would start with regularly distributing evacuation maps to residents of low-lying areas. When a hurricane is to hit, the most at-risk neighbourhoods are ranked. Evacuation capacity is measured and schedules set (e.g. X neighbourhood to evacuation before Noon on Monday, Y neighbourhood after Noon). If the smallest easily-communicated neighbourhood would still overcome evacuation routes, ration by e.g. last number or letter of license plates. If the storm is likely to hit before the last group gets going, pre-position resources (e.g. sand bags, generators and fresh water) there. Since the high-risk were evacuated first, these areas should be both less-intensely and later impacted. Finally, police entry points to stop rule breakers. Police the routes themselves, and don’t be shy about arresting and shaming people who panicked or thought they were better than everyone else.