The ALG report is from 2003; these numbers have fluctuated a bit, and there was some padding that TfL did by arranging so that major street construction programs were complete around the time the charge began; the numbers for 2004 were much worse.
Read the Wikipedia article; I think it's got a lot of good info in it.
http://en.wikipedia.org/wiki/London_congestion_charge
I think the summary for London is:
- Not much change in congestion - Huge, corrupt, expensive, invasive boondoggle
Recent changes are threatening to invert the whole thing: the zone was made bigger and now far more residents (who get a 90% discount on the fee) are driving again in London after being shut-out for 5 years. The original zone didn't have many residents, it was mostly commercial ...
Here's a nice, vetted summary of changing traffic:
A report by TfL in early 2007 indicated that there were 2.27
traffic delays per kilometre in the original charging zone. This
compared with a figure of 2.3 before the introduction of the
congestion charge.
(whoops!)
After the scheme was introduced they had measured an improvement
in journey times of 0.7 minutes per km, or 30%. This improvement
had decreased to 22% in 2006, and during 2006 congestion levels
had increased so that the improvement, compared to the year before
the scheme, was just 7%.
(whoops!)
TfL explained this as a result of changes to road priorities
within the zone, delays caused by new pedestrian and road user
safety schemes, and, most particularly, a doubling of road works
in the latter half of 2006.[95] (Utilities were encouraged to
complete planned road works in the year proceeding the congestion
charge, so it would appear that the first year of measurement
used for later comparisons would also have been affected by
streetworks to some extent.[96][97])
TfL's report in June 2007 found that the level of traffic of all
vehicle types entering the central Congestion Charge Zone was now
consistently 16% lower in 2006 than the pre-charge levels in
2002.[25] The conservative Bow Group noted that the main effect
occurred after 11 am.[89]
*shrug*
Doesn't seem like a swimming success, does it?
/jordan