A lot of substances and items are transported by road, sea, rail and air every day. The biggest hazard is created by the transportation of hazardous substances with flammable, caustic or toxic properties. The hazard level increases if such sub-stances are transported through densely populated areas. Traffic intensity, the technical condition of vehicles, drivers’ errors or ignorance and non-compliance with legal regulations are examples of factors that can lead to potential failures in the transport sector. Accidents can cause an uncontrolled release of dangerous gases or liquids, resulting e.g. in environmental degradation or a hazard to humans. The article presents the issues related to the hazards presented by road transportation of hazardous materials. Examples are shown of potential effects of accidents and hazard zones arising due to a release of selected hazardous substances, such as chlorine, ammonia, petrol, diesel oil or LPG.