NTSB chairwoman said bridge is inspected for structural problems twice a year . Investigators still waiting for all clear to go on site . Comment: Accident occurred after engineer could n't get green signal to cross bridge , got OK from dispatcher .
NTSB chairwoman said bridge is inspected for structural problems twice a year . Investigators still waiting for all clear to go on site . Train derailment led to one car being punctured , releasing hazardous fumes . Accident occurred after engineer could n't get green signal to cross bridge , got OK from dispatcher .