The accuracy of lumped element models for single RLC transmission lines is evaluated. To this end a new error criterion is proposed which permits to avaluate the accuracy of the models independent of driving and loading impedance levels. The results of the accuracy evaluation are represented in a concise way under form of a diagram and the use is illustrated by a typical example. In a second part of the paper examples of time domain simulations illustrate how the use of lumped element models can be extended to coupled lines with frequency dependent losses.