What are the penalties if accidentally enter Singapore tunnel with dangerous goods or with trailer with containers?

Hi Eezat! Vehicles transporting dangerous goods such as explosives, flammable gases or radioactive substances are not allowed to drive in all tunnels, including expressway tunnels. Kindly check more details here: https://onemotoring.lta.gov.sg/content/onemotoring/home/driving/commercial-vehicles.html#types_of_vehicles. For penalty wise, I suggest you have to contact Singapore Customs Checkpoints Division at +65 6355 2183 for detailed information.