Sadiq Khan has suggested drivers will have to pay £5.25 to use the Blackwall and Silvertown tunnels when a new toll comes into force.
The Mayor of London has written to transport secretary Mark Harper urging him to consider a discount for low-income residents living in Greenwich, Newham and Tower Hamlets.
He also asked that any financial support would not affect funding for Transport for London (TfL).
It was announced in September last year that charges for the Blackwall Tunnel – a pair of tunnels under the Thames in east London – will be introduced in 2025 alongside the opening of the nearby Silvertown Tunnel.
The proposals for both tunnels were first made by former mayor Boris Johnson, and approved by then-transport secretary Chris Grayling in 2018.
A suggestion of exempting residents of areas surrounding the tunnels was rejected following a public consultation in 2015.
Following the consultation, the suggested tunnel charge level for cars at peak hours was £4, but Khan suggested this would rise to £5.25 today allowing for inflation.
In his letter to the transport secretary, Khan says: "I recognise that the user charges on the two tunnels have been an essential part of the scheme since the previous Mayor included it in his Transport Strategy in 2009, and it is neither financially nor environmentally viable to remove these charges from the tunnels.
"What we cannot allow is the new tunnel leading to more traffic and more air pollution, which would be a terrible outcome for drivers who rely on the tunnels and for residents in the local area.
"The charges and the fact both tunnels will be inside the ULEZ will ensure this does not happen.
"However, I have become increasingly concerned about the impact of introducing a user charge for the Blackwall Tunnel on residents on low incomes living in the neighbouring boroughs.
"When TfL undertook the consultation on a Blackwall Tunnel toll under the previous Mayor in 2015, it was decided only to offer a limited set of exemptions and support, similar to the Congestion Charge, and the idea of giving residents in the surrounding areas an exemption was rejected."
In a statement, a spokesperson for the mayor said: “New plans for the Silvertown tunnel and Blackwall tunnel are vital for the future of East London, particularly for tackling congestion which impacts residents and businesses.
“Tolling both tunnels was the idea of the previous Mayor Boris Johnson and agreed by central Government in 2018.
"However, Sadiq believes more must be done to mitigate the impact on lower income residents in the area.
"The Mayor has asked TfL to spend the next year working on the details of discounts and exemptions for local residents, working in consultation with the boroughs. “The Mayor has also made it clear to ministers that any exemptions and discounts, which might impact income from the scheme, shouldn’t impact future discussions on wider TfL funding."
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