The UK PM emails road pricing signatories, those who signed the petition opposing pricing. His letter is interesting from a number of perspectives, and was clearly written in part by transportation professionals.
However there is an (intentional?) misrepresentation of the induced demand problem hidden in the text.
If it is the “beginning ,not the end of the debate”, it has not got off to a good start. There are several elements missing from the context, though perhaps they will be brought back in:
1) Hypothecation (the British term for earmarking) – money raised from transportation should be spent on transportation (or its impacts). When talking about building facilities the PM says “Tackling congestion in this way would also be extremely costly, requiring substantial sums to be diverted from other services such as education and health, or increases in taxes.” Implying more money for roads from the same gas tax is less money for something else. This is because in the UK the petrol (gas) tax is used as a cash cow to cross-subsidize other sectors of the economy that should be paid for out of general revenue or otherwise. If people instead saw transportation taxes/tolls/prices as paying for transportation services, there would be more readiness to do so.
2) Local decision making – most travel is local, decision making about tolls and pricing should be local (though obviously there are positive network externalities associated with choosing a common technological framework).

In a less than overly popular move, Ken Livingstone has implemented the western extension of the Congestion Charge, as noted in the GuardianProtest greets congestion charge’s westward push BBC devoted almost the entire half-hour of local news last night to the topic.
Several things to note, though the evidence is anecdotal. First, students are on break this week, so traffic levels are lighter. That said, the buses seemed to make much better time.
Second, it is being billed more for environmental than congestion-relief reasons now, so the nominal motive has changed (the underlying motive, punish the car and raise money remains). Paying lip service to carbon reduction is now politically correct, whether or not this is the best way to achieve that end.
Third, the national government’s long-term road pricing scheme is becoming very unpopular with everyone but the environmentalists, as the public rightly sees it as a way to collect more money, rather than manage traffic and improve transportation. Perhaps hypothecation should be restored in England. The road pricing debate is spilling over on the congestion charge. Privacy issues are also re-emerging as critical.
Some of the roads in the old zone were empty enough during the morning that it felt like a ghost town walking around, all the cars are parked, no vehicles are moving. It is not quite that level in the western extension, though better than it had been … but again, this week is break.
I do believe a major mistake was made in letting residents of the west get to use roads in the east as if they were local. This will raise traffic levels in the east. A zone system would be much fairer, with perhaps some discount for those in the west. I am sure there were political reasons for this.
If the zone gets extended further, some form of zoning will be necessary, or it will lose all effectiveness.
It will be intersting to see the final analysis on traffic levels. I suspect the government lowballed the official congestion reduction estimates of 4 percent to be able to claim victory when a greater reduction occurs.