For normal operations, the 737 runway width requirement is 45m, but yes, it does operate on 30m under certain restrictions. These vary between countries and airlines, but typically include:
Limitations:
- Minimum runway width 30m
- autoland is not allowed
- specific approval by Department of Aviation and Chief Pilot
- more restrictive cross wind limits, visibility requirements and crew qualifications
Dispatch from/to narrow runways is not allowed in case of:
- nose wheel steering inoperative
- one brake or more inoperative.
Furthermore some VMCG corrections have to be applied for takeoff performance calculations.