That is according to the Mayor's Roads Task Force (RTF), which has published its findings after a year-long study.
As the capital gets more and more built up, roofing or lids will be needed over arterial roads to create new surface space and reconnect severed communities, the RTF's report suggests.
Further use of intelligent systems and technology are recommended to reduce delays at traffic signals, smooth traffic flows and provide road users with the best possible real-time information to help plan journeys.
Enhanced road links and new river crossings are also needed to support new developments, the report says.
The RTF also called for studies to investigate the potential for tolled road tunnels to replace surface capacity that could be used to improve the public realm and public transport and to encourage more walking and cycling journeys, while also enabling a more efficient and reliable strategic road network.
The £30bn required to make this happen is comparable to what is spent on the Tube and rail network, and to what other similar-sized cities spend on their road systems.
Mayor of London Boris Johnson said he welcomed the report “and the bold approach it proposes”. He said: “For this great city to retain its global pre-eminence, it is essential we continue to invest and have the courage and vision to develop and drive forward innovative solutions.
“This is a fantastic contribution and I look forward to working with partners, including those represented on the RTF, in taking many of these ideas forward.”
Task force member David Leam, infrastructure director at business lobby group London First, said: “On rail, London is planning for future growth with bold projects like Crossrail 2. We now need to be similarly visionary for London's roads. With road congestion in London costing the UK economy £4bn a year, we need a radical new plan to keep London moving, including new road links and tunnels. Only in this way can we create the world class public spaces and revitalised high streets that will ensure London remains a globally competitive and attractive city.”
An example of building over main roads is, coincidentally, progressing well in Portsmouth at the moment, where BAM Construction is building the Somerstown Community Hub over the A2030 Winston Churchill Avenue (pictured below). By spanning the main road, it will tie together two parts of the community that are divided by the dual carriageway. This is a potential model for what the London Roads Task Force is recommending.