The same thing happens on the railways worryingly often.
Five years from now, all the overblown hype and vote gaining will be finished with and the status quo will have resumed. The government relies on the tax that Air and Road travel bring. Spending massive amounts on the railway isn't necessarily in their best interests because not an awful lot can be gained from it. Look at Manchester. The council gave people a choice - better public transport but with a congestion charge or nothing. The people of Manchester chose nothing in an overwhelming majority - 80%. What the councils should be looking at is ways to improve public transport without squeezing more money out of people. This will not happen however and leads me to believe that all the optimism surrounding the future of Britain's railways is all just false hope. Heathrow is vital to the government coffers.
The London congestion charge is another such farce. It is now free if you drive a 'green' car and £25 a pop if you drive a 4x4. This is apparently to improve the environment, but I can guarantee this would change immediately if everyone bought 'green' cars.
Yes there will be a few more trains but, let's be honest here, they are badly needed. There still isn't anything future proof. All we keep hearing about the railways is speculation, never anything concrete. I am an advocate of the railways and am one who embraces spending fully but I am also a realist and, realistically, many of the things speculated on cannot be achieved without some form of compromise, if at all.
All of the tax you talk about is more than swallowed by external costs to society: Congestion (latest cost £23billion per year), poor health, lost GDP in accidents, police, Climate change and so on, that's exactly why the tax is levied - to tax away externalities. Economics 101. As congestion is particular makes business very uncompetitive, and most of the benefits of any transport are see outside the farebox in terms of connectivity, agglomeration, social inclusion and so on, I wouldn't be quite so negative, its about benefits to as a whole.
As congestion, noise and pollution continue to be a problem for other modes, I wouldn't rule anything out just yet. As you say, the congestion changing isn't popular so, what is the answer? Road pricing was an attempt to correctly value external costs.
Towns like Swindon, Peterborough, Reading, Ipswich and many others benefit from fast rail links, in terms of business and labour markets. The SE commuter towns all benefit from money earned in London and spent in their areas, on local business there.
These aren't my ideas, you don't have to agree with them, but that's how these things are assessed as any decent transport degree or consultant will tell you.
What happens in 5 years will depend on public pressure, concerns at the time and available money. But you are right in saying they actually deduct tax lost from public transport schemes, which is totally wrong in my opinion. I think HS2 was supposed to have something like 45 billion benefits to the UK or something and crossrail works the same way. I'm actually fairly optimistic about the future, but i don't know exactly what it will bring, we shall have to wait and see.
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Externality
An economic side-effect. Externalities are costs or benefits arising from an economic activity that affect somebody other than the people engaged in the economic activity and are not reflected fully in PRICES. For instance, smoke pumped out by a factory may impose clean-up costs on nearby residents; bees kept to produce honey may pollinate plants belonging to a nearby farmer, thus boosting his crop. Because these costs and benefits do not form part of the calculations of the people deciding whether to go ahead with the economic activity they are a form of MARKET FAILURE, since the amount of the activity carried out if left to the free market will be an inefficient use of resources. If the externality is beneficial, the market will provide too little; if it is a cost, the market will supply too much.
One potential solution is REGULATION: a ban, say. Another, when the externality is negative, is a tax on the activity or, if the externality is positive, a SUBSIDY. But the most efficient solution to externalities is to require them to be included in the costings of those engaged in the economic activity, so there is self-regulation. For instance, the externality of pollution can be solved by creating PROPERTY RIGHTS over clean air, entitling their owner to a fee if they are infringed by a factory pumping out smoke. According to the Coase theorem (named after a Nobel prize-winning economist, Ronald Coase), it does not matter who has ownership, so long as property rights are fully allocated and completely free trade of all property rights is possible.
http://www.economist.com/research/Economics/alphabetic.cfm?letter=E
