(4)The lack of interoperability is a significant problem in electronic road toll systems where the road fee due is linked to the distance covered by the vehicle (distance-based tolls) or to the vehicle passing a specific point (for example, cordon pricing). The provisions regarding the interoperability of electronic road toll systems should therefore apply only to those systems and should not apply to systems where the road fee due is linked to the time spent by the vehicle on the tolled infrastructure (for example, time-based systems such as vignettes).