Rail commuters can expect trains to arrive more frequently - especially during off-peak periods, even as the number of delays across the network has come down.

The Land Transport Authority (LTA) yesterday said operators SMRT and SBS Transit will increase the number of train trips per week by more than 1,000.

On the North-East Line, SBS Transit has added more than 400 train trips a week so trains arrive every three to five minutes off- peak instead of four to seven minutes.

On the North-South and East- West lines, SMRT will add more than 400 trips a week to reduce off-peak waiting times to less than five minutes by September. Trains are already arriving every five minutes or less at certain off-peak periods.

As for the Circle Line, SMRT will launch another 150 trips a week next month on top of the 200 train trips a week that have been added since Jan 1.

Trains now arrive every seven minutes during off-peak periods.

Transport Minister Lui Tuck Yew said last year that commuters will eventually wait no longer than five minutes for trains during most off-peak periods.

Meanwhile, figures from the LTA showed that the number of train delays had decreased last year. There were 309 incidents that led to delays of more than five minutes across the MRT network last year, down from 396 in 2012. The figures exclude the newly opened Downtown Line stage 1.

The number of delays lasting more than 10 minutes also dropped from 51 in 2012 to 36 last year. However, there were eight disruptions lasting more than 30 minutes last year, the same as in 2012.

The LTA attributed the improvements to "targeted measures" introduced by joint teams it formed with SMRT and SBS Transit after a spate of severe breakdowns in 2011 and 2012 across the various MRT lines.

For the North-East Line, SBS Transit and the LTA have found a more sturdy material to replace the existing stainless steel U-shaped bolts and counterweight wires that form part of its overhead power supply.

The joint teams found corroded bolts and wires had led to three major disruptions on the line. SBS Transit expects to replace all the cables by this year, and all U-shaped bolts by next year.

The operator will also invest in technology that allows it to monitor the overhead power system more regularly. It has set up "recovery bases" at strategic stations along the line to fix faults more quickly.

Circle Line operator SMRT expects to finish replacing all power cables by the end of this month. SMRT has also adopted new technology that allows it to detect faults sooner on the North-South and East-West lines.

Its vice-president for operations maintenance Low Chin Hun said an automated detection system has been set up at Outram Park, Toa Payoh and Lavender stations to pick out flaws on a train's current collector shoes, which draw power from the third rail.