An IATA official has recently been quoted as saying that, 'A slot management system is indicative of a failure of governments or airports to invest in adequate infrastructure to keep pace with airline demand.'

Should governments and airports always invest to meet airline demand?

Consider the issue of de-peaking. Until recently, airlines worked on a hub-and-spoke basis, scheduling large numbers of flights in and out of hub airports in 3-4 waves each day - early morning, lunch time, late afternoon, and evening. They all connected with each other and then flew off again.

Surprise, surprise - this caused overloading of facilities at peak times and under-utilisation out of those peaks. What did airlines do? Why, they de-peaked at key airports.

Aircraft still came into hub airports in those waves, but their departure was sometimes re-scheduled so that the peak load on check-in and baggage staff was reduced.

So - by IATA's argument - airports should have invested in capacity for the peak caused by the historic hub-and-spoke operation when that became fashionable. They would, of course, then have been left high and dry by the subsequent de-peaking, having invested in long-life assets which the users no longer wanted!

Consider the fact that aircraft are mobile assets and airports are not. Some airlines will - rightly - try a route for a season or two to see if they can make money out of it. If they can't, they pull out. So what should the airport do? How much should they invest for an operation which might not last beyond tomorrow?

And consider the impact of frequent flights by small aircraft or less frequent ones by larger aircraft (an issue studied, incidentally, in ACRP Report 31, available on the TRB web-site).

If an airline schedules a 50-seat plane every half hour instead of a 100-seat plane every hour, it takes up twice as many slots for the same number of passengers. OK, on this one you could argue passenger convenience - all other things being equal, people prefer frequency. But is it really worth it - is it a good use of scarce runway and slot capacity?

Is it worth increasing capacity - as IATA suggests - for this kind of thing?

To me, the killer argument here is that of San Diego. This is the busiest single runway airport in the United States, handling 17 million passengers a year. It has spent much time, money and effort looking for ways to increase capacity because, it is said, it's full.

But look across the Atlantic, to Gatwick - the busiest single runway airport in the world, handling exactly twice as many passengers! The key difference is aircraft size.

The predict and provide policy - predicting demand then providing infrastructure to meet it - has been discarded in other areas. How much does IATA need to catch up with this? Because another leading IATA manager has been quoted as saying that airports should use their charging system to re-distribute traffic - a peak charge signals the cost of the additional infrastructure needed for the peak.

A colleague recently moved from the aviation industry to the rail industry. The key difference he noticed was that the former was always planning for growth, whereas the rail industry was planning for a steady state.

This led me to wonder what the aviation industry would look like if it wasn't always growing! I have as yet come to no conclusions, but there was an interesting presentation at the TRB Annual Meeting in January which showed that air passenger growth might be slowing significantly.

And, logically, it cannot continue. In my lifetime, fares have continued to drop in real terms, and this has led to the growth in air travel we have seen. Can this go on?

Your thoughts would be appreciated!

This station has recently become much more important to Heathrow Express users. This is because of the change in the operating pattern of the Circle Line, which now no longer serves the City directly from the Circle and District Line platforms. It's good to see that the platform environment has been much improved over the last few weeks.

The main visual impact is light. The station is much more light and airy. At the London end in particular, the area has been significantly enhanced with the demolition of some walls and overhead structures, so there is now much natural daylight.

At the other end, the out-of-use footbridge which only went to the adjacent platform has been removed. This too has created more light and more space.

Some of the clutter has also gone from the platforms.

In addition, the Next Train information system is much better.

As yet, there is no sign of a lift (elevator). This would be a major benefit to passengers with heavy luggage - and at a major London terminus handling a lot of holiday traffic as well as the Heathrow Express, this is a major issue. However, there is space, so we can hope!

Indeed, the facilities for changing level constitute the major remaining drawback. The stairs to the footbridge, the only exit from the platforms, get very congested in the peak (although the staff do their best). And there is also congestion by the ticket machines as you emerge onto the main station overbridge.

But overall, the station is significantly better than it was.

Apparently a carbon audit for Manchester Airport showed that 60% of carbon emissions came from cars and coaches, 20% from planes and 20% from buildings.

Currently 8% of passengers access Manchester Airport by rail (and, it is thought, longer-distance journeys predominate). If this percentage doubled by attracting more passengers from the private car, that would reduce carbon emissions by nearly 5% (8% of 60%).

What's that reduction worth - to the environment, to the neighbours?

And how could it be achieved? The train service is already pretty good - what more is needed? Ideas, please!

At the end of March, the UK Department for Transport issued its "Transport Carbon Reduction Delivery Plan".

A major problem I have with it is the downbeat attitude to freight transfer from road to more benign modes. This is typified by the use of statistics which, while no doubt true and accurate, are downright misleading. Moreover they've been known to be misleading since the mid 1970s.

The report, on page 64, says that, "68% of all road freight movements (measured by tonnes lifted) are within the same region and so are unlikely to have a viable mode shift option".

Let's set aside the fact that historically some of the heaviest freight flows in the country - by tonnes lifted - have been within the same region: these are flows of coal for power stations.

But let's look at two important factors.

First, we're talking carbon reduction. And that is a function, not of tonnes lifted, but of tonne-kilometers moved. 100 tonnes moved 20 kilometres use a lot less carbon than 100 tonnes moved 200 kilometres: you need the distance factor to measure the potential importance. Tonnes lifted is irrelevant.

Second, in 1974 a book called "Changing Directions" was published (and I remember, as a post-graduate student at Birmingham University, meeting some of the team who wrote it). This showed the the importance of distance very vividly on page 229.

The then Department of the Environment had calculated that the maximum amount likely to be transferred from road to other means was only 1.5%, based on the average length of haul of road freight travelling over 25 miles.

However, "Changing Directions" made the point that, if there was a mode transfer away from road of 60% of the road freight in the 150 miles and over range, 40% in the 100 - 149 mile range and 30% in the 50-99 mile range, the figure would be very different. About a quarter of all road tonne miles would be removed to other modes.

"Those who cannot remember the past are condemned to repeat it" (George Santayana).

The Council on Environmental Quality (CEQ) - part of the Executive Office of the President of the United States - has issued draft guidance on consideration of the effects of climate change and greenhouse gas emissions in projects. An assessment is likely to be necessary if a proposed action is likely to cause emissions of 25,000 metric tonnes of CO2 or more.

The draft guidance is on the web-site of the White House (see the CEQ website).

So just in the interests of curiosity, I tried to work out the CO2 impact of Heathrow Express. I was helped by work some colleagues have been doing on the carbon impact of transport generally.

This gave me baseline statistics for fuel consumption (cars - 7 litres/100 km), emissions (petrol car 2.76 kg CO2/litre and diesel 3.17) and the conversion factor for kg of CO2/vehicle-km (0.19 petrol, 0.22 diesel). The emissions for electric trains are 0.05 kg CO2/passenger-kilometre.

The road distance from Paddington to Heathrow Terminal 5 is 29.8km: by rail it's 26.2.

OK, not all Heathrow Express users start from Paddington or go to Terminal 5, but it's a reasonable journey for the comparison.

Multiplying kg of CO2/km by distance gave the CO2 emissions/trip.
Heathrow Express carries 4.93m passengers a year: the emissions related to that amount to 6,461 tonnes of CO2.

Suppose Heathrow Express didn't exist? I assumed that those 4.93m people would access the airport by private car or taxi in the same proportions as other passengers do now. I also assumed the cars were petrol and the taxis diesel powered. Car mode share is 35% and cab 27%, so I allocated 56.5% of Heathrow Express trips to car and 43.5% to taxi.

I assumed that if people accessed the airport by car, the car would come back again - they'd be kiss and ride trips. If they came by taxi, the same cab would be used by different people in different directions. So I doubled the figure for car users.

Tonnes of CO2 emitted by the vehicles of road users hypothetically unable to use Heathrow Express came to 46,255 - about seven times the tonnage of Heathrow Express.

Wow!

Now ok, there are several heroic assumptions in all this - but it does give an order of magnitude figure.

Moreover, coming back to the original cause of this research, it shows that an airport express serving an airport under 30 km from the city carrying under 5 million passengers a year can save 40,000 tonnes of CO2 - significantly more than the CEQ guideline.