Faculties & Forums General Discussion

An interesting debate has cropped up within the committee of the Aviation Forum, but I think it needs a wider airing. It was prompted by a recent Waterfront conference, Aviation Policy in the Shadow of Climate Change, and the assumption that an increase in public transport access to airports is an environmental benefit. One experienced committee member disputed this, quoting the Royal Commission on the Environment, which apparently determined that most forms of public transport are less energy efficient than small cars. Unsurprisingly, this assertion triggered an exchange of detailed e-mails!

Former Aviation Forum Chairman and expert on surface access to airports, Alastair Duff, observed that consistently applied policies in favour of public transport have clearly reduced the percentage of single occupant cars accessing certain airports. Additionally, multiple factors are involved, including air quality as well as congestion.

The current Chairman, Vernon Murphy, has pointed out that even successful public transport services require a certain passenger volume before they can truly exploit their relative energy efficiency. Another nice assertion is that neither Heathrow or Gatwick could handle current passenger numbers without their respective dedicated rail services.

Anyone else care to throw their hat into this particular ring?

The need for surface access to airports is being driven by air travel (fairly obvious I know) and the ongoing rise in air travel.  Looking at the whole journey, the amount of pollution generated by the journey to the airport must be fairly small compared to the flight itself.  Whilst increasing the modal share of public transport to airports is environmentally beneficial, the existence of the airport isn't.  The environmental impact of car access also includes the ridiculous land take required for car parking as against not very much for a bus or rail station.

 I'd argue that first and foremost demand restraint is needed on air travel - no airport expansion, tax on all domestic flights.  That'll cut down on the need for surface access in the first place.  Then some of the proceeds can be spent on improving public transport links.

Trevor Whelan started this discussion by talking about surface access to airports, but Dominic Davidson diverted it to a suggestion that air travel as a whole is environmentally unsound.  I would suggest that anyone who would like to understand the situation should come to the forthcoming multi modal transport solutions conference due to take place in October, organised jointly by the Institute and the Royal Aeronautical Society.  I hope we will hear some objective and balanced views based on real research.

 But returning to the original subject, I would like to offer a few thoughts.  Air travel is already a significant surface trip generator and, whatever amount of growth takes place, there is a need to ensure that surface access to airports is efficient and sustainable.  For air passengers, the key determinant is whether you are travelling outbound or inbound.  If you are a 'local' the chances are that your origin is not in the city centre and you will have access to a car.  If you are a visitor, the city centre is much more likely to be your destination and you will not normally have a car available.  It is this, more than any other factor like journey purpose, or even the relative mertis of the available modes, which mostly determines whether you will use public transport to and from an airport.  Think of your own air journeys.  Most likely you will start from home, maybe get your partner to take you to the airport or maybe drive yourself and park.  At the destination end, you're much more likely to get a train, but, coach or taxi.  Think then of visitors to any airport and the reverse happens. No doubt there are many exceptions, but the data demonstrates that this is the most important factor.

 Once the basic public/non public transport choice is made, then issues such as price, journey time and quality come into the decision.  Air passengers who are 'time poor, money rich' will choose a fast premium mode like Heathrow Express, while budget holidaymakers may look for something cheaper but slower. 

No two airports are the same in terms of catchment, market profile or geography.  The current situation relating to rail links to Glasgow and Edinburgh Airports is a good example.  These are similar sized airports, but the prospects for a rail link at Glasgoiw are significantly better than at Edinburgh, for a variety of reasons.

 The focus on air passengers can also hide the issue of how staff get to and from the airport.  There may well be as many surface trips by staff as there are by air passegners.  Staff are there before passegners start to arrive and after they have all gone, so have particular trip requirements that require services around the clock seven days a week.  Some public transport, such as local high frequency bus services, can serve staff very well.

Lastly (for the time being) don't be too harsh to condemn airport car parking.  A 'park and fly' trip means one surface access trip for every one way air journey (or less if there is more than one passenger per car).  A 'kiss and fly' involves two surface trips per air trip.  Which is the more effiicient and sustainable?

When I raised this issue in the aviation forum I had hoped that the relatively simple case of airport access had allowed studies that might have illuminated the issues of mass transit vehicle capacity utilisation and the consequent impact of different transport modes on emissions. 

I have always been uncomfortable with the quality of the argument that transferring demand between transport modes can reduce emissions.  This partly due to vehicle physics, if constructed of similar materials a larger capacity terrestrial vehicle tends to be heavier per unit capacity than a smaller vehicle.   This seems to be borne out by experience.   Lightweight material are equally usable by all modes and rail vehicles require a minimum weight for traction so despite the low rolling resistance of steel on steel there are grounds for expecting a disadvantage that railway vehicles busses and coaches must overcome through higher capacity utilisation.  Unfortunately, where peak trough ratios are high and service frequency is important it is not good logistics to expect higher capacity utilisation from larger vehicles.   This is reflected in a great deal of data.   Even the 18th report of the Royal Commission on the Environment published in table 12.2 data that showed all rail energy intensities as inferior to the coach and some, notably the electric suburban vehicle, as inferior to the car.    This data was tentative but we now have in the public domain the Rail Safety and Standards Board paper Traction energy metrics.  The data from this is usable to show the difficulties of assuming any benefit from road rail transfer.

The data gives energy intensity per seat kilometre and typical capacity utilisations.   Unfortunately we only have the electrical power consumed at the vehicle for rail vehicles drawing on centrally generated power.  The report addresses this by referring to the emissions of carbon dioxide from the different types of generating plant and the plans for their future use.   Coal plant is the most polluting and is expected to provide 10% of electricity through 2022 because the may be a shortfall in gas generation the actual proportion generated by coal may be greater than 10%.  The report discusses three approaches to estimating the emissions from power used by the railway.

From the data, and using the emissions from coal burning we can calculate comparative CO2 emissions

I have added figures from other sources for the small diesel car and there is considerable informed discussion of the availability of still lower energy intensities for this class of vehicle.  

The data has an inherently high degree of uncertainty; for example, it is difficult to predict the trends of capacity utilisation for road and rail, if rail must increase frequency to match the utility of road vehicles then capacity utilisation could reduce as ridership increased while increasing fuel prices may increase car sharing and thus increase car capacity utilisation.    The data also ignores the emission costs of consolidating loads except for stopping and starting and ignores the substantial emissions from building new facilities to expand rail capacity.  The Author also suggests that, except for city centres, despite its high speed rail does not offer significant door to door advantages in travel time compared to the car or coach.  

The author suggests that only differences in emission figures of 20% can indicate a high probability of a real difference.    The author also suggests that because of their long life more efficient rail vehicles will not be available for decades.   It can be seen that no rail vehicle is significantly better than a ten year old small car or even the average cars entering service in 2022.    It can be seen therefore that increasing the proportion of small car use is the best option for reducing transport emissions overall and that increased use of the motor coach for longer distance journeys is a far better option than rail.    On these data shifting demand from road to rail is not a good option for reducing passenger transport emissions.

Bus does not offer a significant advantage over the small car and may not always attract sufficient passengers to justify bus priority or offset the negative impact of so large a vehicle on congestion.  On this evidence perhaps the determinant of bus policy in most locations should be how favourable its impact on social deprivation is. 

The figures are of course very sensitive to capacity utilisation.  The data in the report are variable.  In the table above 20% is used for the proportion of places (ie including standing) used on the bus.   31% is used for all trains and this may be too high for commuter trains absorbing road traffic.  It is tempting to assume the 20% figure for bus as more likely.   Air uses 70% and coach 60%.  These may be seem anomalously high although smaller vehicle size and high frequencies do lend themselves to pushing up capacity utilisation.  It is often commented that aircraft increase capacity utilisation by the very aggressive marketing of discount fares but rail too uses this technique.  Rail may achieve better than 31% on some lines but these lines may not sustain this if they must run extra trains to accommodate new peak traffic.

Aircraft are subject to one other issue, the energy intensity per pax km has multiplied by 2 to allow for radiative forcing but the aircraft spend very little time at the relevant altitude.  Someone who knows more about this than me may be able to suggest a better factor.

Jim Russell.

I feel somewhat diffident about entering this particular fray, since I missed most of the earlier correspondence - I was too busy with my day job when it first blew up. Also while I've looked at both the RCEP report and the RSSB report mentioned by Jim Russell, I have not studied them.

However, I don't think the former helps. That table (12.2) is about longer distance passenger travel by mode - and NOT short distance city to airport travel. Because of this, some of the statistics favour car rather than rail (considering both as an airport access mode). (1) Trains are assumed to have a 22% load factor - this is much more typical of the Bristol - Weymouth or Crewe - Cardiff kind of journey than the Heathrow - London journey. (2) Cars are assumed to have a 35% load factor - this is reasonable for longer distance journeys, but loads of 1.4 (small car) or 1.75 (large car) look high for cars at airports - especially business oriented airports. OK, kiss and ride trips have a load of 1.5 - but offsetting this, they make make 2 journeys for each air passenger journey (which is inefficient in emissions terms, however useful it may be to those doing it). (3) Cars are significantly more efficient on longer journeys than shorter hops - the 70 miles/hour trip on a motorway gives better fuel consumption than the stop-start down the A23 to Gatwick. So I'm not convinced that the evidence in this report is fit for the purpose for which it is being used.

I also looked at (but did not study) the RSSB report Jim Russell referred to. At the bottom of page 5/top of page 6, it says, "The comparison of rail with other transport modes confirms that electric trains are at least as efficient as other means of transport in terms of grams of CO2/passenger-km. As electricity supply is "de-carbonised" the benefit will increase so that they become at least as good as double deck diesel buses, despite their much higher average speed and passenger acceptability. On environmental grounds, there is a strong case for transferring passengers from road and air to electric railways meeting their energy targets discussed above." It goes on to discuss diesel trains (less good environmentally) - and, of course, diesel trains are used to reach Manchester and Cardiff airports, whereas electric trains are generally used for most others in the UK - Gatwick, Heathrow, Stansted, Southampton, Birmingham, Newcastle, Prestwick and in future Glasgow and Edinburgh.

The comment in the RSSB report about de-carbonising becomes particularly relevant if you move abroad. In Sweden, 99.6% of the electricity used for rail comes from hydro: the remainder from wind-power (Banverket's Sector Report).

I believe that the role of the Institute, as one of the few pan-modal bodies around, ought to be to disentangle  statistics like these and present an impartial case. The Road Haulage Association can say how wonderful trucks are these days, IATA can say how little the pollution planes emit these days and the AA and RAC can pronounce in the interests of their members. All of this no doubt makes them feel warm and comfortable inside, but no-one outside those industries is convinced. We can be impartial: I believe we should be, and we should do our best to dig deeper into the evidence to tell people what it really means.

Hi

I love your last paragraph because it is where I started with all this.  

If you had had time to dig deeper ypu would have confirmed that electrical de-carbonisation is one of the central issues.  Unfortunately the UK is not likely to achieve much very quickly because of the long lead times for low carbon generation and because of the security of supply issues that will constain growth.

The other fundemental is capacity utilisation.  It would improve debate if operators published their load kilometres and capacity kilometres.

Anyway I still cannot find adequate evidence to suggest Bus and Coach really are less environmentally polluting than ten year old small diesel cars.

Jim

Some other food for thought.  In Aberdeen, the airport recently stated that it intends to introduce bus/taxi lanes within and around the airport (without creating additional roadspace) as a way to promote sustainable access.  Current bus travel to the aiport will be in the region of low hundreds per day however there is a vibrant taxi trade (due to lack of bus services) and a massive dependancy upon car use.

There has been a local backlash against the proposal which is a massive change in transport policy for a commercial body that is currently very dependant upon car access and is clearly looking to the future in terms of sustainable travel.

Its a clear example of someone putting their money where their mouth is in terms of sustainable transport policy!