SRC helped found Cofiroute (Compagnie financière et industrielle des autoroutes) in 1970, taking a one-sixth of the share capital in this highway concession company designed to develop the French highway network. During the 1970s, highways A10 Paris-Poitiers, A11 Paris-Le Mans, A71 (Paris-Orléans) were completed. Cofiroute was the first private highway concession company at the time, and at the end of 1979, had the longest network in service, with 508 kilometers in total. Colas' stake in Cofiroute was sold in 2014.

In the 1970s, traffic was growing quickly and roads required increasingly efficient bituminous binders. In collaboration with Shell, Colas developed Colflex®, a range of bitumen modified with SBS elastomers (styrene-butadiene-styrene). This modification gives the bitumen elastic properties that guarantee exceptional resistance to traffic and aging. That kind of bitumen is still used in the present day.

SRC continued to gain ground in North America. The company consolidated its positions in Canada. Sintra expanded out to Alberta and in northern Canada in 1977. The Group established a presence in the United States by acquiring assets in 1979 that led to the creation of the Group's first US subsidiary, Barrett Paving Materials.