A variety of nonlinear follow-the-leader models of traffic flow are discussed in the light of available observational and experimental data. Emphasis is placed on steady-state flow equations. Some trends regarding the advantages of certain follow-the-leader functionals over others are established. However, it is found from extensive correlation studies that more data are needed before one can establish the unequivocal superiority of one particular model. A discussion is given of some ideas concerning the possible reasons for the existence of a bimodal flow versus concentration curve especially for multilane highways.

A discussion is given of the gap acceptance problem confronting a driver at a stop sign who is attempting to cross a single lane of traffic. This problem is discussed in the light of a gap acceptance probability that is taken in the form α(t) = 0 when t < T and 1 − α(t) = exp[−λ(t − T)] when t > T, rather than a step function as has been considered in the past. Some experimental information is discussed concerning the values of the parameters λ and T in such situations. This information coupled with theoretical considerations allows one to estimate quantities such as mean delay time, probability of zero delay, and highway transparency. Comments are made concerning the influence of car performance on road crossing and on entering highways.