Before the charge's introduction, there were fears of a very chaotic few days as the charge bedded down. Indeed Ken Livingstone, Mayor of London and key proponent of the charge, himself predicted a "difficult few days" and a "bloody day". In fact, the first two days saw a dramatic reduction in inner city traffic. On the first day 190,000 vehicles moved into or within the zone during charging hours, a decrease of around 25% on normal traffic levels. Excluding 45,000 exempt vehicles, the decrease was more than 30%. Anecdotal evidence suggests journey times were decreased by as much as half. Just over 100,000 motorists paid the charge personally, 15–20,000 were fleet vehicles paying under fleet arrangements, and it is believed around 10,000 liable motorists did not pay the due charge. An extra 300 buses (out of a total of around 20,000) were introduced on the same day. Bus and London Underground managers reported that buses and tubes were little, if at all, busier than normal. Initially it was suggested that the reduction in traffic was caused by the half-term school holidays, but this has proved not to be the case. Reports consistently indicate that, over the first month or so of operation, traffic was down at least 15% on pre-charge levels (the first week had a decrease of 20%).
On 23 October 2003 TfL published a report surveying the first six months of the charge. The main findings of the report were that on average the number of cars entering the central zone was 60,000 fewer than the previous year, representing a drop in non-exempt vehicles of 30%. Around 50–60% of this reduction was attributed to transfers to public transport, 20–30% to journeys avoiding the zone, and the remainder to car-sharing, reduced number of journeys, more travelling outside the hours of operation, and increased use of motorbikes and cycles. Journey times were found to have been reduced by 15%. Variation in journey time for a particular route repeated on many occasions also decreased. The report said that the charge was responsible for only a small fraction of the drop in retail sales. The report also stated that around 100,000 penalty fines are issued in each month. Around 2,000 are appealed against. The larger than anticipated reduction in traffic numbers meant that TfL revenue would be only £68 million — well below the £200 million per year expected by TfL's first projections in 2001. In practice, once the extensive roadworks undertaken in London during 2001-2002 were lifted in November of that year, TfL found traffic levels had dropped noticeably, and the profit projection was lowered to £130 million per year. Once the charge came live in February 2003, traffic levels dipped again, hence the much lower revenue than expected.
A further report published by TfL in October 2004 stated that only seven of the 13 government aims for London transport would be met by 2010. The target on reducing congestion for Greater London will not be met, the report said. In 2006 the latest report from TfL stated that congestion was down around 26% in comparison with the pre charge period and traffic delays had also been reduced. It also says that the charge appears to have no impact, either positive or negative, on road safety — the slow trend towards fewer accidents has continued. In comparison, during an experimental Stockholm congestion charge there has seen on average a 25% reduction in congestion.
Reports have shops and businesses being heavily impacted by the cost of the charge, both in terms of lost sales and increased delivery costs as recognised by the London Chamber of Commerce. In August 2003, the John Lewis Partnership announced that in the first six months of the charge's operation, sales at their Oxford Street store fell by 7.3% whilst sales at other stores in the Greater London area but outside the congestion charge zone rose by 1.7%. However London First's own report indicated that business was broadly supportive. Subsequently another report stated that there had been a reduction in some employment in the charging zone. TfL criticised the reports as unrepresentative and that its own statistics reported no effect on business.
A report in May 2005 stated that the number of shoppers had declined by 7% year-on-year in March, 8% in April and 11% in the first two weeks of May. TfL countered that an economic downturn, the sars outbreak and threat of terrorism were likely factors. At the same time a London Chamber of Commerce report indicated that 25% of businesses were planning on relocation following the charges introduction. However an independent report 6 months after the charge was implemented suggested that businesses were now supporting the charge. London First commissioned the study which reported that 49% of businesses felt the scheme was working and only 16% that it was failing. The Fourth Annual Review by TfL in 2004 indicated that business activity within the charge zone had been higher in both productivity and profitability and that the charge had a "broadly neutral impact" on the London wide economy.
It has been estimated that due to the West London extension in February 2007, 6,000 people will eventually lose their jobs.
Transport for London have recorded falling particulate levels within the original congestion charge area and along the Inner Ring Road boundary zone. Nitrous Oxide (NOx) fell 13.4% between 2002 & 2003 along with similar falls for Carbon Dioxide (CO2) and Particulate Matter (PM10).