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.