ISB1101: Staggered Scheduling

Take note: with the New ISB Network implemented from 19 July 2021, route information in this article is likely to be outdated.

Here’s an example of a service improvement many of us might have overlooked: bus departures on services A1 and D2 are alternated. We stagger the schedules of A1 and D2 buses coming out of PGP.

This helps us to achieve a higher frequency along the congested PGP-UHC sector while using the same amount of resources.

How does it work?

PGP is the start of the route for both A1 and D2. Remember that in Bus Scheduling, I explained that only the trip start timings are regulated, by means of the driver logging his trip on a computer.

Technically, A1 drivers will log their trips at PGP while D2 drivers actually do their logging at Carpark 11. However, since both services have the same first stop, we are still able to alternate their trips.

Consider the example of timings around 1pm, when it’s not rush hour. (I picked this example so that the numbers wouldn’t get too confusing.) The frequency for each bus is 10 minutes, for example. So in theory, the maximum waiting time you have for a bus would be 10 minutes.

However, if we alternate the departures on A1 and D2, making them five minutes apart of each other, we could achieve a maximum 5-minute wait time for the same journey.

Imagine if we have A1 departing every ten minutes. The buses might depart at 1.00 pm, 1.10 pm and 1.20 pm. Meanwhile, D2 would also depart every ten minutes, but the timings would be 1.05 pm, 1.15 pm and 1.25 pm.

As you can see, this translates to a maximum waiting time of five minutes for any bus that goes to Kent Ridge MRT.

What do we stand to gain?

Since A1 and D2 ply the same route from PGP all the way to Opp UHC, this means that this high-traffic stretch is served by buses at twice the frequency while using the same number of buses are before.

This will be a game-changer not just for PGP residents, who have an easier time getting to Science. It also benefits students in FASS, SoC and Business who are heading to Kent Ridge MRT in the evening.

Technically, from these three faculties, it’s faster to travel to the MRT via PGP (using A1), as the distance is shorter and the crowds are less dense.

However, many students are put off by the fact that they have to alight from the A1 at PGP and wait for another bus, be it a new A1 or a D2. It’s not so bad actually, because you have two choices of bus to wait for, but the idea still puts people off.

But now that the schedules are adjusted, I can confidently that the waiting time there has been reduced to a minimum. And yes, this means it is faster to go that way. So head home via PGP today!

2019 Update: As of May 2019, Service D2 has been amended to begin at Opp TCOMS. However, it has actually always been departing from Carpark 11 (behind Business), so the staggered schedule is unaffected. You may continue making journeys the shorter way!

2021 Update: As of July 2021, ISB D2 now starts and ends at PGP, but A1 and A2 pass through PGP without a layover as they now layover at Kent Ridge Terminal, rendering this entire article outdated. Everyone now travels the shorter way!