Running the future Cross Island Line (CRL) under the Central Catchment Nature Reserve is the better choice (Cross Island Line: Running under nature reserve or skirting it both feasible, says LTA, Sept 3).

Tunnelling 70m below ground would have no impact on the ecology and biodiversity of the reserve, and building ventilation structures on 3ha of forest next to the reserve will cause only temporary damage and loss of habitat to endangered wildlife.

When the area is restored to its original condition after the line is completed, nature will replenish the ecological footprints.

Skirting around the reserve will incur more construction cost, irreversible damage with property acquisition and six more minutes of travel time per trip.

The CRL will have 30 stations, half of which are interchanges with existing lines providing projected 600,000 daily trips.

The saving of six minutes for each trip will add up to a huge saving in productive time.

The 4km of MRT stretch which serves no residents is negligible compared with the skirting option's additional $2 billion in construction costs, property acquisition, engineering challenges and longer travelling time.

The potential safety problem if a train stalls along the 4km stretch is manageable. The maximum distance from the forest to its boundary is only 2km.

Build a well-ventilated and brightly lit path with three to four 500m-long moving walkways for emergencies. They can be used to evacuate passengers to the nearest station. The process will be fast, with minimum walking.

The cost of no-frills emergency moving walkways travelling at a speed of 0.5m per second is not expensive compared with long-term energy savings and productive time of commuters.

Paul Chan Poh Hoi