Just over a week back on 18 August 2017, the latest addition to Singapore’s metro system, the Downtown MRT Line, broke down during the morning peak period.
We have looked at similar train disruptions in the past, but the Downtown Line presents an interesting context. Unlike it’s older counterparts like the North-South Line and East-West Line which have bus services routed based on the hub-and-spoke model, the Downtown Line doesn’t share the same design guidelines. As such, the resulting impact of a line failure might not be as predictable as it initially seems as access to alternate transport and routes may vary from station to station along the line.
Also, unlike the previous write-up, this time we will look at both the reach and impact of the line failure.
Here we define reach as the areas that are affected by the line failure, and what is the loss in mobility. Impact on the other hand is defined as how these areas are affected, and what kind of delays do they experience.
Having developed a toy index for accessibility based on locations of hawker centres, we can take a look at the reach of the the line failure by looking at the effect the failure has on the accessibility index.
As a quick recap, the Hawker Centre Accessibility Index measures mobility by looking at the number of hawker centres accessible from a starting point within an hour on public transport.
By comparing the difference in the accessibility index between regular train operations and during the line failure, we can get a sense of which areas are most affected and disrupted by the failure of the Downtown Line. In the plot above, the brighter the area, the greater the loss in accessibility or mobility.
As mentioned above, bus services around the Downtown Line have not been routed based on the hub-and-spoke model, with a number of bus services running pretty much in parallel to the line. As such, not all areas along the line are affected to the same degree. Notable affected areas are the areas around Cashew, Hillview and Sixth Avenue stations.
Reach tells us which areas are affected by this line failure, but it doesn’t describe how these areas are affected. To look at impact, we have to look at the time delays and its distribution depending on origin and destination.
Even being just one station apart, the line failure has very different impacts on Sixth Avenue and Tan Kah Kee stations, seeing an additional 10-minute delay to equivalent destinations if departing from Sixth Avenue station instead of Tan Kah Kee station. Note that this is the time delay on top of the usual travel time, thus the travel time between stations have already been accounted for. Another similar example is between Cashew and Hillview stations.
On the other hand, with immediate access to alternate routes via other metro lines, the impact on interchange stations like Botanic Gardens and Chinatown stations are less pronounced. Especially with Chinatown station where there are not snowball effects from the line failure, with the delays only affecting areas mainly served by the Downtown Line.
As usual, the assumptions made here are that there are no spill over effects (which is unlikely) from the line failure onto the alternative routes. So in a sense, this represents the best-case scenario during the failure.
“So what does this mean if we get caught in a disruption?” asked one of the boys in the office.
If you haven’t, you should check out the write-up on isochrone maps that led to this analysis.
Appendix: Impact along the Line
Appendix: Impact outside the Line
Originally published at swarm.is.