The safety of the Mass Rapid Transit (MRT) system in Singapore was questioned by the public after several accidents on the system during the 1980s and 1990s. Most problems have been addressed, and many safety measures are visible to users of the system. Significant incidents 5 August 1993 (7:50am) – Two C151 trains collided with each other at Clementi, resulting in 132 injuries. The collision occurred because a work train that did maintenance work earlier that morning had spilled oil onto the tracks. One of the trains on that stretch of track that morning had been unable to brake in time because of the oil, resulting in a collision with a stationary train which was waiting to move off upon the recharging of its brakes. 9 October 1997 (2:00am) – A maintenance train derailed in the tunnel near Toa Payoh. The derailment occurred because a staff member had failed to reset the track alignment properly. Disruption to train services between Bishan & Newton lasted about 8 hours. 13 April 1999 (10:00am) – An empty C651 train on its way back to Bishan Depot after the morning peak service derailed between the Yio Chu Kang and Ang Mo Kio. The derailment occurred because the station master had failed to reset the track alignment properly. Disruption to train services lasted about 7 hours. 23 April 2002 – 21 C751B trains were withdrawn from service due to faulty gearboxes, though there were no safety implications. There were reduced train services on all lines resulting from this shortage of trains. 3 March 2003 (7:30pm) – A car crashed onto a stretch of at-grade track along Lentor Avenue in between Khatib and Yio Chu Kang, resulting in a light, minor collision by an oncoming train. Disruption to train services between along this section of the line lasted almost 3 hours. A construction accident occurred at approximately 3:30 pm on 20 April 2004 in Singapore when a Circle Line tunnel being constructed near Nicoll Highway station collapsed. The supporting structure for the deep excavation work failed, resulting in a 30-metre (100 ft) deep cave-in that spread across six lanes of Nicoll Highway. The collapse killed four people and injured three. The accident delayed the construction end date for the MRT station. The accident left a collapse zone 150 m wide, 100 m long, and 30 m deep. Four workers were killed, with three more injured. Steel