I fully agree with you about going through the city. However, it appears that its legal to transport hazmat through town:
Hazard Overview: Hazardous Materials Incidents in Baltimore
Hazardous materials (HazMats) are part of our economy. They are used to make an array of commercial and industrial products which we consume and rely upon for various purposes. In Baltimore City, there are over 200 facilities that manufacture and/or store hazardous chemicals at threshold quantities. These are known as “Tier II Facilities,” and they are required to report to the Maryland Department of the Environment on the types and quantities of chemicals at their respective locations. Every day, hazardous materials are also transported through Baltimore via railroad, trucks, and ships. Companies that manufacture, store, and transport hazardous materials are responsible for adhering to federal, state, and local requirements to ensure that these materials are handled safely and do not threaten public health. When HazMat incidents do occur, the Baltimore City Fire Department and the Maryland Department of the Environment play the primary role in responding to and mitigating the incident.
https://emergency.baltimorecity.gov/sites/default/files/hazmat information.pdf