Wednesday, 23 December 2015

Bus fleet replacement

Something odd is happening to our local bus fleet. 

All the buses that serve the Exeter to Exmouth route have been replaced together.  And all the vehicles are dedicated to that route.  So the company has acquired eleven new buses,  branded them as "Stagecoach Gold" with comfortable seats, wi-fi, USB sockets at the seats.  The timetable hasn't been significantly changed, but the service has been relaunched with gold coloured buses, labelled all over with the route name and number.  (Link here for the story.)

It seems odd to have a large bus fleet and then to divide it into - what shall we call them? - sub-fleets which cannot be interchanged.  Naively, one would expect that it would be more efficient if no vehicle was dedicated to a particular route.  Then, when wear and tear meant that one vehicle needed maintenance or other attention, any of the other similar vehicles could take its place.  But a bus which is labelled "Exeter to Exmouth" on the side cannot be used for the route from Exeter to Barnstaple.  And the buses that go between Exeter and Barnstaple are plain, and would not be appropriate for the Exmouth service.  So, I deduce that there must be enough flexibility in the Exeter-Exmouth sub-fleet to ensure that the service can be supported with vehicles of the same colour and quality. 

It isn't the only local route which has its own sub-fleet.  There are other "gold" bus routes out of Exeter and Plymouth.  But this is the route with the most regular service (every 15 minutes during the day).  In due time, I expect other local bus routes to have their own dedicated sub-fleet.  The same branding is being used in other parts of the UK.  The USB sockets are a new feature compared with buses that were rolled out in the Midlands.  For some time we have had "ordinary" buses branded with a particular route; however, those could have their branding removed or changed quite easily, should the need arise.  The point about this latest change is that the new vehicles are quite different in styling and facilities.

So, let us speculate and try (as O.R. people) to unravel the decision-process that has been followed.  A decision has been made to introduce this quality service; that means it has to be marketed in competition with the railway line and travel by car.  So the decision follows that all the buses on the service must be of the same appearance and standard.  Then this leads to the size of the sub-fleet, and here cost appears, balancing the need for facilities to keep these vehicles on the road with the extra revenue to be expected from the improved service.  Somewhere along the line, there is an advertising budget, which has been quite small in comparison with the cost of a double-decker bus.  (And decisions have to be made about how to advertise the service.)  Some of the costs are offset because the new transport has released a dozen or so older buses into the pool for the whole local fleet. 

Other commercial vehicle fleets have similar problems, whether they are trucks or trains.  But there are relatively few situations where a whole sub-fleet needs to be rolled out overnight.

And I like the new buses - because, in addition to the facilities mentioned - they have more legroom!

A multicriteria analysis of access to UK airports

How easy is it to get to an airport?  Recently, the UK newspaper, The Independent, attempted to measure access to a couple of dozen UK airports.  Without using the term, they performed a multiple criteria analysis using three surrogate measures that affect access to airports by public transport.  So, they used: the fare, the journey time, and the waiting time. For each of them, the smaller the better.  They were measuring from the city that was nominally served by each airport, although, in practice, that city will not provide all the passengers for the airport.  But, on the assumption that many people who use public transport to get to an airport will travel through the main city, it isn't too bad an assumption.  (When Tina and I travel from London Heathrow, we use rail and bus and do not go via London - there is generally little point in going into London from the west and then going out to the airport which is to the west of the city.  But we are in a minority.)

How do you develop a measure which combines these three?  The newspaper multiplied the three measures together to get a number whose dimensions were (minutes)^2 * pounds, and then took the cube root to bring the numbers down to a manageable size (and that did not affect the ordering at all) 

Exeter, our local airport, is 20 minutes away by bus, and the bus is every hour, with a fare of about £3 so the three measures combine to give 20 * 60 * 3 = (15.3)^3.  
From the newspaper's report:
This generated a league table (see below) where low scores show better transport links.
The clear winner, Southampton, should hardly be a surprise; it has frequent seven-minute train connections from Southampton Central to the Airport Parkway station, barely four miles from the city. More impressive, arguably, was the performance of Birmingham and Manchester – much bigger airports, twice as far from the cities they serve.
Airports rated: the lower the score, the better
1 Southampton 7
2 Birmingham 7.5
3 Manchester 8
4 London City 8.5
5 Heathrow 9
6 Aberdeen 9.5
7 Newcastle 10
8 Belfast City 10
9 Edinburgh 11
10 Glasgow 11
11 Leeds/Bradford 12 
12 Bristol 13 
13 Liverpool 14
14 Exeter 15
15 Inverness 15
16 East Midlands 17
17 Belfast International 17
18 Prestwick 17.5
19 Cardiff 18
20 Gatwick 21
21 Luton 21
22 Stansted 24
23 Southend 26

The analysis could be extended:  for us in Exeter, the local airport scores 15 on this measure.  Suppose we wanted to go to Bristol.  There is an hourly service, Rome2Rio says it would take 87 minutes at a cost of £55.  That airport, for us, would score 66.  And Heathrow: 257 minutes (via Woking), hourly service, fare £43, scoring: 87.  Southampton, top of the table for its home city, scores 71 for travel from Exeter.  But I have no cause to fly from there, because - when it comes to comparing airports for personal use - the choice of destinations affects me.  Southampton has fewer destinations than Bristol or Heathrow, so doesn't compare withthose two airports.

So, it is interesting to see how a newspaper attempts to compare items (airports) on the basis of these three criteria.  Would an O.R.  professional have used the same measures?  And made a similar comparison?  

As an aside, over the years, I have flown from from nine of the airports listed.