Tuesday, May 27, 2008

Service costs and spreading the peak - 2

As well as fares and frequency, another way to spread the peak is to provide express services during shoulder peak. Generally expresses are even more 'peaky' than train frequency. This is good for inner-suburban passengers (as it gives inner suburban stations a broad peak of frequent services) but less favourable for outer suburban commuters who have increased travel times relative to if they travelled during the height of the peak.

The following times indicate the first and last peak direction express trains passing through Caulfield (or Camberwell). 'Express service' is defined as one not stopping at five or more stations*.

AM Peak

Belgrave/Lilydale: 5:46am - 10:20am
Cranbourne/Pakenham: 6:12am - 8:36am
Frankston: 7:43am - 8:47am

PM Peak

Belgrave/Lilydale: 3:40pm - 7:37pm
Cranbourne/Pakenham: 4:41pm - 6:06pm
Frankston: 5:16pm - 6:21pm

(*) Based on 30/9/07 timetables, which are out of date. Will be updated with new data.

The main limitation of the above spans is that they change according to where you draw the line on the number of stations the expresses miss. For example, there are many trains that express through three stations. This will broaden the span - to most of the day in the extreme case of the Frankston line where it becomes meaningless.

Because it's better to spread the peak and this requires both service and behavioural changes, I opted only to include the faster express trains. This is in line with passenger behaviour - passengers able to will prefer the faster expresses, even if the travel time saving is small. Shoulder travellers on some lines pay a penalty in reduced service frequencies and/or fewer expresses, and tackling this is helping to spread the peak and increase efficiency.

What do the above lists show? The Belgrave/Lilydale lines have wide peak express spans, with express services running well into the shoulders. The Frankston line has very narrow peak express windows (literally 'peak hour'), although it has many lesser expresses outside those times and during the day. Cranbourne/Pakenham has expresses opearating during most peak times. The most conspicuous gaps where there are no or slow expresses are on the Frankston line before 5pm and on both the Cranbourne/Pakenham and Frankston lines from about 8:30am. These early finishes do not encourage 9:30am starting, though if this was encouraged the after 6pm services also need attention.

The narrow express peaks on the Frankston line warrant further attention. Planning for it is complicated by the interplay with the other Caulfield group lines. Service priorities are elsewhere and nowhere is the competition fiercer but on the Caulfield group. The number of Frankston expresses appear to be held back by a need to provide a service to inner suburban stations (Malvern - Hawksburn) that cannot be satisfied by existing Carrum, Mordialloc, Cheltenham, Westall and Oakleigh local trains alone.

Current arrangements have the advantage of relieving the burden on the Cranbourne/Pakenham line (which has heavier patronage but less infrastructure). However Frankston is also a long line with its own distinct needs. These are a wider selection of expresses to serve areas beyond about Moorabbin and more frequent service closer in.

This makes the concept of a two-tiered service based on frequent local and express trains running over a longer span attractive with better use of the existing third track to Moorabbin. However it could also mean that some zone 1 stations (eg Glenhuntly or Carnegie) may lose express trains, and more services would miss the loop, running direct to Flinders Street.

To summarise, spreading the peak by making shoulder peak service more attractive is a viable way to improve capacity and network efficiency. While it can't cope with meeting long-term requirements, it's a worthwhile short and medium term strategy to relieve pressure on the network and has an exceptional return per dollar spent.

Wednesday, May 21, 2008

Service costs and spreading the peak - 1

What gives best 'bang for the buck' when it's decided to use service levels as a lever to boost patronage or change patronage patterns (eg spreading the peak)?

Whether you look at it from the customer side (better services) or the supply side (costs and resources), the answer is rather 'lumpy' and not linear.

As an example, adding an extra three trains per hour to a subway service that's already running every three minutes isn't going to make the service that much better, assuming the existing system is already reliable and is not overcrowded. On the other hand, using them to increase an hourly service to every fifteen minutes is a major boost and makes the service much more attractive.

On the supply side, the costs in boosting services escalate as follows:

Stage 1: Existing infrastructure sufficient, existing rolling stock sufficient, need to train/roster more drivers.

Stage 2: Existing infrastructure sufficient, need more rolling stock, need to train/roster more drivers.

Stage 3: Need more, infrastructure, need more rolling stock, need to train/roster more drivers.

Stage 1 is the fastest and cheapest, while Stages 2 and 3 are the dearest and take longest.

Additional peak capacity is likely to require Stage 2 or 3. In contrast, major improvements to off-peak services only require Stage 1. This explains why the marginal costs of increasing off-peak patronage is lower than increasing peak riders. If some of the latter can be induced to shift their travel times to shoulder peak periods, total patronage grows and the large fixed costs of rail are spread across more passengers, increasing efficiency.

Against this is a question as to transport's role in society. Should transport adapt itself to people's lifestyles, or should we expect people to change their living according to what suits the transport system? The former will obviously cost more than the latter, since more Stage 2 and 3 improvements will be needed to cater for a sharp peak. However public transport economics can't afford to impose itself too heavily on passengers, since more will find driving more attractive, train patronage will stagnate and modal share will fall.

To date the main measures that have been taken to spread the peak include:

1. Local bus improvements. Many routes now finish at 9pm instead of 7pm. This may lengthen the evening peak, although there is still a frequency penalty for those leaving work after about 6pm.

2. An 'early bird' ticket. A special ticket providing free travel for train travellers (only) who reach their destination by 7am. Intended to spread the morning peak.

3. Some increases in shoulder period train services.

The following graphs compare current service provision across the AM and PM peaks on several popular lines. For those not from Melbourne, the lines can roughly be described as follows: Belgrave/Lilydale: 3 tracks for better peak expresses, high service levels and low catchment population growth; Cranbourne/Pakenham: 2 tracks, moderate to high service levels and high catchment population growth; Frankston; 3 tracks for better peak expresses, moderate service levels and moderate catchment population growth. All are at least 40km long and have stations every 1 to 3 kilometres. Suburban services on the latter two lines also have to share with goods and/or country trains.

All trains that pass through the nominated points are counted; even when they do not stop. Using a moving time period (rather than fixed 30 minute blocks) would be better, but is not needed for broad comparisons.

Apart from the intensive services on the Belgrave/Lilydale line, the major distinguishing feature is its extended morning peak. This compares to the Dandenong line (especially) where service falls to off-peak levels by 9am. In this regard the Frankston line does better, though its frequency is less during the 'early bird' period.

During the evening, the broad peak on the Belgrave/Lilydale line is again apparent. Frankston again has the shortest peak, with the period of significantly enhanced service lasting for about two hours. Possibly due to its third track and relaxed capacity constraints the general pattern is that the Frankston line runs faster expresses (but fewer of them) than the Cranbourne/Pakenham lines, which has more stopping trains, but better frequency.

Of the lines surveyed, the Cranbourne/Pakenham lines have the least infrastructure, the most non-suburban trains to share with, the highest overall patronage and the greatest patronage growth. This causes its peak services to be under a degree of pressure unseen on the Belgrave/Lilydale line, as reflected in the reliability statistics. This makes it the most attractive candidate for peak spreading, particularly around 9am, 4pm and 7-9pm.

Tuesday, May 20, 2008

My Grandma owned a car

Transport academics and leaders talk about the future for Melbourne public transport (2 parts).

Discussion at the Future Melbourne wiki.

Thursday, May 15, 2008

Investment, risk and success: making interchanges work

Though they sound like something from a business seminar, today I will demonstrate that these finance-like concepts are key to effective passenger interchange.

To transfer from a train to a bus requires investment in both time and physical effort. Ideally this effort is small, as with efficient interchanges and able-bodied passengers. But in others passengers may need to climb stairs, negotiate busy roads and walk several hundred metres. Especially in poor weather or with older passengers the 'investment' and energy is significant. And passengers do make calculated decisions based on these hard-headed criteria.

Still on the business theme, there's risk and success. Risk is the chance of the attempted transfer not working. If the passenger perseveres, the main consequence is a long wait (if a bus has just been missed). If they abandon the transfer, the passenger might retrace their steps, walk home or call a taxi. In both cases they are unlikely to risk the transfer again, assuming they have alternative transport. Success, in contrast, generates repeat patronage the next time that trip is needed.

Successful interchanges require the following:

1. Low investment/low commitment. It should not require much effort to make the transfer. Should it not work out, little time will have been wasted, and other routes or alternative transport can be used to complete the journey with minimum delay.

2. Low risk/high success. Information increases certainty and certainty lowers risk. If the bus is not due for a while, passengers must know about it as soon as they alight the train (eg from bus timetables at station exits), and not until after they've trekked to the bus stop on the other side of a major intersection. The waits themselves can be minimised by co-ordinated bus scheduling. Variability in access time and the chance of missing buses can be reduced with direct walkways, underpasses and crossings. Good wayfinding signage improves navigability and passenger errors. All these lower risk and increase the chance of success.

To summarise, low investment, low risk and a high chance of success is what makes a winning business proposal. Successful transport interchanges are no different.

A successful interchange

The diagram below shows a small but successful transport interchange. The three elements that make it so include information, access and service co-ordination.

Some of the new bus/rail interchanges on the Perth suburban rail system can claim to score highly, since passengers can scarcely alight from a train without bumping into a bus timetable. Werribee in Melbourne is one of our better examples, with good access and service co-ordination, but some limitations with information.

An unsuccessful interchange

Below illustrates a poor interchange. Passengers alighting from the train have no idea of bus times. Station exit locations maximise walking distance. The road might be difficult to cross as no provision has been made for pedestrians. There is a high chance the bus will have left before passengers will have been able to reach it, but long waits are equally likely due to poor service co-ordination.

Epping Station* is one of our better examples of a poor interchange, with its main redeeming feature the co-ordinated TrainLink bus.

(*) Though monies have recently been budgeted for this interchange to be upgraded.

Wednesday, May 14, 2008

Crowds, delays and late-running - Part 2

It's only slightly harder to find a parking spot in a car park that's 91% full than one that's 90% full. It might take 33 seconds instead of 30 seconds, for example. However it's twice as hard to find a spot where it's 99% full instead of 98% full. Finding one would take twice as long on average. And when it gets really full, from 99 to 99.9%, you'd expect parking would take 10 times longer, since there's only 1/10 the number of free spaces.

This is the rule that even a tiny increase in usage of a system nearing capacity causes service faults (or more accurately, their impact) to rise exponentially.

In Melbourne we are currently experiencing the same on our peak-hour trains. Operators struggle to meet performance targets and rising patronage is cited as the key reason why. Today's stats compare to five years ago, where the likelihood of your train being late or cancelled was 50 to 70% less, but patronage was also lower, and if your train was cancelled you were more likely to be able to board the next one.

Studying lateness and cancellation figures is useful but don't always tell the full story, especially as seen by the passenger. In some cases a cancelled train may be effectively replaced by the previous running late, and the overall impact might be negligible. But in others, even a 2 minute delay could cause buses or other trains to be missed, resulting in 15 - 60 minute delays. Similarly the cancellation of a busy service might lengthen waits as passengers are unable to board the next three or four crush-loaded trains.

For simplicity, let's assume that trains can carry 1000 people crush-loaded. An on-time morning peak train approaching Station A already has 800 on board. As 80 people board at this station, all can board.

The same is also true for the next station (Station B). By the one after that the train will be full, but assuming some alight (eg a nearby school is a popular destination) then Station C's 80 people should also just be able to fit on.

The situation changes if the train departs late.

For a start there will be more on the platform at previous stations, as some intending to catch the following train will have started walking on. The total number of people walking through the validators at all stations before Station A could be 50 persons per minute (but may be more).

If all these people board, and the train departs the terminus 3 minutes late, then that's at least 150 extra people on board by Station A. With 950 people already, and at least 80 wishing to board, then at least 30 will be left behind. With the crush load train presenting at Stations B and C, most of their passengers will be unable to board.

Why did I say 'at least'? The graphs in Part 1 show that as a train approaches capacity, boarding time rises exponentially. So the train will likely be 5 or more minutes late at Station A, and even later down the line. And in that time more people (say 5 or 10 more per minute on average) will have passed through the validators at Stations A, B and C, all expecting to catch the train. So the train could well be full even before it reaches Station A.

Hence we have three station platforms of passengers, increasing every minute, unable to board the train. The next train, assuming it left on time might be emptier than usual on leaving the terminus, as some of its passengers will have boarded the previous late-runner. And for a while it might even be only a couple of minutes behind that train, its progress retarded by the slower-loading train in front. However as it travels more of its passengers will be comprised of those left behind than the increasingly delayed earlier train, and early arrivals for the train after that. So the second train that started on time could end up also being late and crowded.

On the busier lines in Melbourne, this and the following several trains will also be leaving passengers behind. And at the more inner stations (especially those served by one line only and bypassed by expresses) passengers may need to wait for several trains to pass before being able to board. This causes the actual delay experienced to be higher than what might be apparent from train running data alone (as some trains were unboardable).

To summarise, a line with frequent trains that are not crush-loaded (eg Belgrave/Lilydale) will outperform ones that are (Pakenham/Cranbourne and Sydenham lines) in reliability. Belgrave/Lilydale are nearer the 90% carpark full level, while the others are like 99%. And it's much easier to find 100 passener places in a hurry to clear a platform on the former than the latter.

Tuesday, May 13, 2008

Crowding, delays and late-running - Part 1

A points failure, lightning strike or level crossing accident delays thousands of passengers on a busy line. Some get frustrated and blame the train operator. Others take refuge in a good book. But for me such incidents are beneficial in that they force me to think about them and their management. I confess that blog postings here would be fewer if I lived on a shorter, quieter and less delayed line!

The following graphs illustrate some links between passenger loading, delays and their propagation (click for a larger image).

Saturday, May 10, 2008

Low-tech passenger information

Passengers would need to be blind or stupid not to notice this:

One way to advise of cancelled trains:

Simple? Yes. But blackboards do the job, cost almost nothing and reflect well on the station staff involved. They are labour-intensive, especially if they need to be changed and/or are on platforms away from the main building. It is at large stations and nearby bus stops that electronic displays come into their own, at the cost of flexibility and (possibly) loss of local control.