Del. Code tit. 29, § 8229

It is the intent of this Act that this be the exclusive state method of regulating and controlling the transportation of hazardous materials. To that end all acts and parts of acts, ordinances and regulations elsewhere promulgated or enacted are hereby repealed and declared unenforceable to the extent that they are inconsistent herewith. No city, town, municipality or other subdivision of the State shall adopt or enforce any other regulation of the transportation of hazardous materials. This shall not preclude the State from regulating hazardous wastes and hazardous substances, including the transportation thereof, as may be otherwise provided by law.