The scale of the problem has been highlighted in the West Midlands where nearly 150 metal theft incidents were recorded on the regions motorways last year.
There were 149 incidents in the region in 2011-12, compared with seven in the previous year, a Freedom of Information request from the BBC Inside Out team revealed.
It cost about £5.9m to repair and replace the metal across England in 2011-12, the Highways Agency estimated.
Darshan Ubhi, of the Highways Agency, said there was a “great deal” of new technology introduced as part of “managed motorways” in the Midlands, when electronic signs indicate vehicles can use the hard shoulder during congestion.
He said: “What’s been targeted is the communications and more importantly the power cable that is feeding all of these devices.”
PC John Martin, from Central Motorway Police Group, said the price of copper had increased “massively” over the last two years.
He said: “As a product to be stolen it’s actually very high value and it’s quite profitable, even when it’s sold as scrap.”