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on Environmental Quality (CEQ) - part of the Executive Office of the President of the United States - has issued draft guidance on consideration of the effects of climate change and greenhouse gas emissions in projects.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The draft guidance is on the web-site of the White House (see the CEQ website).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.

On the Thameslink route between Bedford and Brighton (and connecting Gatwick and Luton airports), the rolling stock is being changed. The old class 319s are being replaced by new class 377/5s.

The new trains have a better ride, and a more up-to-date (but quirky) information system.

What they don't have is more seats.

The 319s had 319 seats in a 4-car set - certainly as built. Some sets were changed subsequently, and there is much grousing among seasoned commuters when a train rolls in with Sunny South Special seating, complete with bar snug area and fewer seats, designed for non-stop London - Brighton trains.

The 377/5s, however, seem to have 241 seats in a 4-car set.
I say "seem to" because the plates on the end of the cars says there are 241 standard class seats - even though there are first class seats at each end.

Let's assume they do have 241 seats - that's about 75% of the seating of a 319 (75.549, if you must!).

Aha, say the Department for Transport, who control these things, just wait a few years and all of the stations on the route will accommodate 12 car trains.

Well, yes, but it's here and now!

And a 12 car 377/5 only has 723 seats - 85 (26%) more than an 8-car 319.

Progress?