Mock explosive devices, such as thunderflashes were detonated near-simultaneously in subway trains and station platforms at four MRT stations (Dhoby Ghaut, Toa Payoh, Raffles Place and Marina Bay) and in a double decker bus at Toa Payoh Bus Interchange. A chemical agent attack was then simulated at Dhoby Ghaut at 6:45 am. An undetonated mock bomb was also placed at the Raffles Place. About 3,400 commuters who were on board the subway trains were evacuated during the drill. Services at 13 MRT stations were temporarily disrupted and roads within the vicinity were also closed to traffic. Shuttle buses were used to ferry commuters affected by the exercise.