The first stages of modernization of the Vestfold Line were carried out through a combination of new trains and sections of double track. Vy ordered of the Class 70 trains for their InterCityExpress services in 1988. Capable of speeds of , they were introduced on the Vestfold Line in 1992. The new trains increased capacity on the Vestfold Line with 2,100 seats per day. Vy soon found that the four-car trains had an unsuitable size: a single unit did not provide sufficient capacity while two units provided too much capacity. Despite the upgrades, by 1997 the trains from Larvik to Oslo were using twenty minutes longer than they were in 1973, and the average speed on the Vestfold Line was down to .