present in the same degree in dealing with free public highways. Highway departments have built the existing roads with definitely limited funds and it has been their problem to distribute these funds over the roads under their control so as to meet the most urgent traffic requirements. Provision of facilities has always lagged behind the evident needs. Often a needed widening of surface has been deferred in order to meet more pressing demands for surfacing earth roads or to replace low-type surfaces with more durable construction. Any system of highways constructed with public funds for the free use of the public must be designed on the basis of compromise, and all highway users have been inconvenienced at times by the lack of both wide and smooth surfaces.
It is understood, however, that these conditions must either be accepted or that funds must be provided more rapidly for their correction. The prospective user of a toll highway will regard lack of adequate width in an entirely different light. He will be in a position to choose between the free and the toll route. To attract the motorist the toll roads must offer advantages that loom larger than the tolls charged. There must he no retarding of traffic flow because of lack of width. Therefore the traffic volume at which a toll facility should be widened is inevitably much lower than that at which free highways have been widened. To provide unrestricted movement of the traffic anticipated 20 years hence requires wide pavements at relatively low present volumes.
PAVEMENT WIDTH DEPENDENT ON MAXIMUM RATHER THAN AVERAGE VOLUMES
In considering the possibilities of self-liquidation of any toll highway, the measure of use must be the total volume for a year or some average volume that takes into account seasonal fluctuations. Estimates of probable use are prepared on such a basis for use in financial studies. But such figures do not indicate the necessary widths of pavements because width must be based on the maximum estimated traffic that will use the road at peak periods throughout the year. Not only does the average daily traffic for any month vary considerably from the average on a yearly basis, but also the traffic on the different days of the week varies to a similar or an even greater degree.
To provide means of determining the probable maximum daily and hourly traffic volumes from the estimated average daily volume on the selected routes, records from a number of automatic traffic recorders were analyzed. Selection was made of records from highways on which the fluctuation of traffic was thought to be comparable with that which may be expected on the routes of the selected system.
The results of this analysis are shown in plates 23 and 24. Plate 23 shows that with an average daily volume of 1,500 vehicles, for example, the average daily volume in the month of maximum traffic may be expected to be 2,000 vehicles. Plate 24 shows that 2,000 vehicles per day correspond to a maximum hourly traffic of 520 vehicles.
The next step was to establish a relation between traffic volume and needed width on a toll road. Recently, the Bureau of Public Roads has conducted studies of highway capacity in which exhaustive analysis has been made of the movements of all vehicles using highways of
