Monday, December 20, 2010

A season for pruning? Part 2: Options for the Sunshine – Melton corridor

Part 1 identified some ‘dead wood’ routes; that is bus routes that had a purpose when started but now largely parallel others. They would be the first place to start if looking for efficiencies on the bus network.

Redundant routes survived because new bus funding outstripped planning capability, which had atrophied in the 1990s ‘bus drought’ when there were few new services to plan. By the time expertise returned (often consultants hired for the bus reviews) money for their full implementation was running out, at least in established areas.

Scrapping redundant bus routes in favour of upgrading others a further round of improvements, but this time without large additional funding. Unfortunately there is only so much you could do with simply axing ‘dead wood’ routes as they amount to no more than a few percent of total service kilometres.

Larger change requires defter hands in which the skills of the artisan, composer and economist are at least as important as those of the axeman. Artisan because the hand requiress a careful eye and trained mind that sees the network as a whole. Composer because it is within the beat set by train arrivals that buses are best planned. And economist because they value efficiency and understand opportunity cost.

A bus corridor makeover

I will present an example where rethinking a pair of routes may improve overall service levels and connectivity. The routes chosen include the western portion of Route 216 and all of Route 456. Together they form the main bus coridor between Sunshine, Caroline Springs and Melton. Two alternatives to the current timetables are discussed. Each has its own pros and cons. Hence there is always a need to consider the ‘greater good’ since it’s difficult to make any change without disadvantaging somebody.

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The area and services

Sunshine is an established rail-based centre populated largely by low-income migrants who use buses heavily. Its shopping centre and timetabled crossing of trains in both directions make it an ideal interchange hub. Caroline Springs is a 1990s housing estate built remote from the railway with only a basic bus service. Melton is served by country trains and has an older core surrounded by new housing. Unlike Sunshine, Melton is polycentric, with the railway station, main street shopping strip and enclosed shopping centre beyond easy walking distance from one another. Suburban trains operate every 20 minutes to Sunshine. Two bus routes, run by different companies, leave there for Caroline Springs; Route 216 (which has come from the city) and Route 456 (which extends to Melton). Both bus routes run approximately every 30 minutes, so do not connect with trains every 20 minutes. And neither do they mesh with one another, so they do not form an even 15-minute service. In addition Route 216 terminates just short of the Caroline Springs Town Centre so its coverage is very limited.

How many buses?

It’s useful to know how many buses are used on current routes so that changes can be costed. The number of buses depends on route length and frequency. It can be estimated from the timetable, either numerically or graphically.

During weekday off-peaks Route 216 takes 20 minutes to get from Sunshine to Caroline Springs. The 30 minute service provided would need 2 buses if run as an independent route. Due to the efficiencies gained by continuing this service beyond Sunshine, the actual requirement may be slightly less – let’s assume 1.8 buses to be safe.

Route 456 takes 55 minutes to do the trip to Melton. Hence a single bus can go there and back every 2 hours, meaning that the existing 25-30 minute service would need 4 buses.

Any resource-neutral service improvement would need to use no more than 6 buses. If it could be done with 5 buses it may be possible to free a bus for a route that needs it more.

Summary of the existing service

The departure list below shows existing weekday off-peak services and their connectivity with ex-City trains arriving at Sunshine.

The above shows that each train is followed by at least one bus. However connection times can be up to 20 minutes. Being significant compared to travel times (approximately 25 minutes to Caroline Springs and similar by train to the city) connection times have a large influence on end-to-end travel speeds and the relative attractiveness of public transport.

I did not examine connections for other travel patterns (eg city-bound train to bus & bus to train, but the uneven bus service intervals indicate likely similar results.

Here’s some key numbers:

Estimated number of buses used: 5.8 approx
Connectivity with train: no
Services per hour (Sph): 4.25 (measured over 4-hour period)
Average Bus frequency (Favg): 14 min (=60/Sph)
Maximum Bus wait (Wmax): 21 min
Maximum Train-Bus connection: 20 min
Service efficiency (ie Favg/Wmax) = 67%

Although the average bus frequency is 14 minutes (between Sunshine and Caroline Springs), maximum waits can be up to 21 minutes as the routes are not scheduled together. Worst case train connections are a similar figure, although most are better.

In the sample time period there are six more buses than required to consistently connect with each (off-peak) train. Connection quality varies due to unharmonised bus headways. Just missed connections are common; on six occasions the bus departs within two minutes of the train arriving. And effective frequency is lower than the 14-15 minutes it would be if services were evenly spaced.

This represents both potential inefficiency and opportunity. For it may be possible to deliver more consistent connections and/or higher effective frequencies with the same or fewer buses.

Scope for improvement?

Some ‘back of the envelope’ attempts to improve schedules are presented below. Not being a professional bus scheduler there will be aspects missed, but the general concepts, borrowed from timed transfer networks worldwide, should still be sound. The complications posed by multiple operators serving the corridor are not discussed. There may be scope to improve efficiencies by swapping routes between operators, or routes could be shared between operators, as already sometimes occurs (eg Route 400 between Sunshine and Laverton).

Option 1: One frequent route to Melton, meeting every train.

Achieved by deleting Route 216 past Sunshine and using saved resources to boost Route 456’s frequency to 20 minutes all the way to Melton.

Approximate bus times are shown on the graph below.

Graphs like these are commonly used by train schedulers. They show how many vehicles are required to run a service and indicate connectivity at interchange points.

Time is shown across the horizontal (x) axis and location on the vertical (y) axis. The steeper the slope of the line, the faster the travel. A horizontal line means the bus is stationary, for instance waiting at an interchange. Each coloured line shows the path of a bus; in this case six are required. The dots near the top signify train times in both directions.

Some numbers below:

Connectivity with train: yes (3 to 7 min in all directions)
Services per hour: 3 (entire corridor)
Average Bus frequency (Favg): 20 min
Maximum Bus wait (Wmax): 20 min
Service efficiency (ie Favg/Wmax) = 100%
Estimated number of buses required: 6

Several points are worth noting:

* The timetable aimed to create a timed-transfer network at Sunshine. Buses arrive, trains arrive, trains depart and buses depart. Passengers can simultaneously transfer in any direction with minimal waiting.

* Sunshine station presents special opportunities for service co-ordination since trains both to and from Melbourne arrive within a few minutes of one another. This doubles the number of good bus-train connections possible. Hence a bus there and back can connect with no less than 4 trains.

* Connection times are between 3 and 7 minutes. Given the standard for on-time train running is within 4:59 minutes, anything under 5 minutes is arguably too tight. It may be possible to adjust bus times by a minute or two to increase the probability of successful connections in peak travel directions.

* Recovery time is nearly all spent at Sunshine rather than Melton (where it is only 1 minute). Spending it at Melton would mean that the bus would arrive at Sunshine too late to make train connections.

* A nine minute recovery time at Sunshine has been scheduled. Buses arrive at :57 and depart at :06, to exchange passengers with trains in both directions around the top of the hour, repeating every 20 minutes. Such dwell times heavily use interchange space, with the bay being occupied nine minutes out of every twenty. However the best measure of bus bay efficiency is passenger throughput, and it is possible that despite the dwell time this could be quite high given the large number of connection combinations possible (4 per 9 minute occupancy, not including bus-bus transfers).

* Measures that could free space at bus interchanges and/or reduce dwell times while preserving connectivity have not been explored. One example is a layover area. Here the bus empties at a drop-off only bay near the station entrance, moves to a nearby layover area and returns to the designated pick up stop in time to leave on time. Another possible tool is ‘active transfer management’ which would also speed buses, especially routes carrying through passengers, such as orbital routes. Here the bus would be scheduled to leave just after the train is scheduled to arrive (say h:04 instead of h:06), but would be held back to at least h:06 if the train is late.

* The tightness of the some bus/train connections and the very short layover at Melton may mean that this timetable might look good on paper but be fragile in practice. It is in these marginal cases where cutting running time by 2 to 4 minutes per direction can greatly improve reliability, connectivity and bus utlisation. Removal of close stops, more direct routes and bus priority at intersections are the sort of cheap projects that could make the difference here.

To summarise, Option 1 is the highest service choice, providing effectively a TrainLink service between Sunshine and Melton. It scores well for frequency, consistency and connectivity. However it does not save buses (compared to the present arrangements) and poorly serves Caroline Springs. It also removes the ability for Caroline Springs residents to catch a direct bus to the city.

I would also wonder whether the service is overkill, and if there are more deserving routes for the resources. Much of the route is sparsely populated and may not justify a 20 minute frequency (this being transit hostile development where the greatest population densities are off the highway). While it is some distance away, the corridor is also served by diesel trains, which offer a much faster (but currently less frequent) service between Sunshine and Melton.

Melton’s population growth is likely to support either a more frequent diesel train or electrification, both of which would further lessen the need for a 20 minute bus service to Melton, since changing to a local bus at Melton Station may be faster than the direct bus from Sunshine.

Option 2: Connection with every train to Caroline Springs, with every second trip extending to Melton.

This option reduces Route 456 to a 40 minute frequency, carefully timed to meet every second train. Route 216 west of Sunshine Station becomes an independent route every 40 minutes to Caroline Springs, timed to provide a 20 minute frequency over the combined portion between Sunshine and Caroline Springs (to meet every train).

The graph below shows how this service might run: (click to enlarge)

It’s messier than Option 1 since two types of service are offered. Three buses provide a 40 minute frequency to Melton with similar times to every second trip of Option 1. In between are Sunshine to Caroline Springs trips, again every 40 minutes, arranged to provide a 20 minute frequency along the common portion. The existing timetable allocated about 25 minutes to do this trip, so two buses are required to operate this service.

Some numbers:

Connectivity with train: yes
Services per hour: 3 (to Caroline Springs), (1.5 to Melton)
Average Bus frequency (Favg): 20 min (40 min Melton) Maximum Bus wait (Wmax): 20 min (40 min Melton)
Service efficiency (ie Favg/Wmax) = 100%
Estimated number of buses used = 5 (Melton 3, Caroline Springs 2)

There are several points worth noting:

* This is a lower service option for Melton, with the non-clockface 25-30 minute Route 456 service reduced to 40 minutes (also non-clockface). However unlike the current arrangement it provides a consistent connection with every second train. And if introduced in conjunction with an improved Melton train timetable the frequency cut may not be missed.

* The Sunshine – Caroline Springs portion (216) would have fewer buses and lose its direct link to the city. However it would gain better train connectivity and a less lumpy timetable. Reliabilty should also improve as delays affecting the Sunshine-City portion of Route 216/219 would be quarantined. Travel to Footscray and the City would remain possible through better train connections or changing to Route 216/219/220 bus (a combined 7.5 minute frequency) at Sunshine.

An initial draft had evenly spaced departures from Sunshine towards Caroline Springs and Melton. However return trips had two arrivals every 40 minutes at Sunshine. This is an effective frequency of 40 minutes or a 50% service efficiency – both unsatisfactory for a corridor with a current 14 minute average frequency.

A way around this is to hold each Route 216 return journey at Caroline Springs by 20 minutes. This gives us a 20 minute effective frequency and a 100% service efficiency, which are both good. However having buses lay over for about as long as they are moving is inefficient.

How could the idle time at Caroline Springs be better utilised? A look at the existing Route 216 terminus indicates it terminates in housing, distant from local trip generators. A short (2km) extension to Caroline Springs Town Centre would lessen idle time, serve a local trip generator and connect with other routes.

This arrangements may save nearly one bus compared to the current arrangements. Possible uses for this resource in the Sunshine area could include: Boosting frequency of Route 471 from 25 to 20 minutes to connect with trains, extending Route 451 north to Watergardens Station, extending Route 454 southwards to the industrial area, extending Route 417 northward to Sunshine to better cover industrial areas, later trips to Derrimut (Route 400), or extended coverage in Sunshine North are all contenders. I will not pick which is the highest priority, but some are likely to attract more patronage than economising parts of 216 and 456 would lose.

Option 3. Melton to Caroline Springs via Sunshine.

This can provide a service outcome similar to Option 2, depending on the treatment of buses at Caroline Springs. Instead of the routes being independent they are interlined, ie buses from Melton do a short trip to Caroline Springs via Sunshine and then return to Melton via Sunshine.

Due to the backtracking and dwell time at Sunshine there are no advantages in this for the passenger. It would only be considered if it allows the service to be run with fewer buses.


The above examples indicate the potential for service planning to improve bus network legibility and connectivity. Two options for the Sunshine – Melton corridor have been presented.


Anonymous said...

Good idea, but in peak times you would need more than a 20min service between Caroline Springs and Sunshine as it can get quite busy.

Craig said...

Good detailed analysis.

Given the bus also passes Albion Station en route to Caroline Springs a few minutes later, the tighter train connections mentioned can probably be tolerated, as the timetable will allow longer conenctions at Albion.

This week highlights another problem on the corridor - different day timetables operating on the 216 & 456 on public holidays.

Paul Nicholson said...

People often use the connection at Albion between the train and the 216 bus.

It has to be one of the least attractive interchange points in the Melbourne metropolitan area.

Route 471 is usually busy during the day especially between Sunshine and the North Laverton industrial area.

At the Williamstown end, route 471 is one of the most attractive bus routes with lovely views across Hobsons Bay towards Melbourne and, at the terminus, across Port Phillip Bay. The terminal area is subject to redevelopment but work has yet to start.

Anonymous said...

Agreed Paul about the interchange at Albion, it needs to be made better.
And Peter while your idea would make it a flat 20min service which in a way is good, but bad things is you'd be going down from 5 or 4 buses an hour to 3, and I dont think 3 buses will handle it, off peak, 9.00am to 3.00pm or in peak.