The Influence of Vehicular Speed and Spacing on Tunnel Capacity

In the flow of traffic through vehicular tunnels, it is shown that an approximate linear relationship between speed and density of traffic exists, whereby, as the average speeds of vehicles increase, the density of the traffic stream decreases. The relationship is used to establish a series of theoretical equations that, in turn, permit the determination of optimum conditions of speed and spacing required to produce maximum volumes under given conditions of traffic composition. The significance of uniform speeds and spacings in moving large volumes of traffic, which is disclosed in this study, has been clearly recognized in practice. In the Lincoln Tunnel in New York City, the Port Authority has established minimum speed limits, banned slow under-powered trucks from the tunnel, and erected a number of signs to influence motorists to maintain a specified distance behind preceding vehicles. All of these traffic control devices are directed toward an optimizing of vehicular speeds and spacings, and have resulted in significant increases in maximum hourly traffic volumes accommodated by the tunnel. Operations Research , ISSN 0030-364X, was published as Journal of the Operations Research Society of America from 1952 to 1955 under ISSN 0096-3984.