Aug 26 (Reuters) - French construction and concessions group Eiffage expects a significant recovery in the second half of the year thanks to the resumption of works and summer motorway traffic, but still sees a marked business decline in 2020 as a whole.

France's third-largest builder behind Vinci and Bouygues on Wednesday forecast slightly lower year-on-year activity in its contracting business, which works in construction, property development and energy systems, predicting lower orders from local authorities and some industrial customers. In its concessions business, which builds, maintains and services motorways and airports, Eiffage warned that potential travel restrictions made it impossible to reliably estimate traffic - despite a summer uptick on its motorways.

Earlier on Wednesday, the French prime minister said the government wanted to avoid a new nationwide lockdown, even as a senior advisor warned a second wave of the coronavirus pandemic could hit France in November.

Eiffage estimated it had taken a 1.83 billion euro sales hit from COVID-19 between mid-March and end-June, as airport and motorway traffic fell and the Pierre Mauroy Stadium was shut.

The group, whose projects also include offshore wind turbines, said that despite restarting almost all works during June, adapting sites to health restrictions continued to weigh on productivity.

Eiffage posted a mid-year operating profit of 262 million euros, down 68.7%, from revenue of 6.92 billion euros, a drop of 18.9%.

However, Eiffage said its contracting order book had reached a record high of 17.1 billion euros, after low production in the second quarter and three major contracts wins this year - France's future A79 motorway, Germany's A3 and the HS2 high-speed rail line in the UK.

The group warned in March that its 2020 earnings would "inevitably fall" due to the impacts of the coronavirus pandemic. (Reporting by Sarah Morland and Dagmarah Mackos in Gdansk; editing by David Evans, Kirsten Donovan)