Those portions of the research project, fundamental characteristics of traffic flow, which pertain to volume and speed characteristics on major urban arterials are reported. Seven study locations in the vicinity of two michigan cities, detroit and lansing, were representative of a wide variety of urban arterials, ranging from a controlled access expressway to a surface arterial with heavy parking along commercially developed frontage. At each of the study locations at least one continuous week of data was successfully collected. This involved: (1) detecting traffic volume, speed, and headway information for each individual lane of the direction being studied, (2) transmitting this information from the detection units to a central office, whereupon (3) the information was summarized on graphical and digital recorders. Various analyses were then performed on the data by manual and mechanical means. The most important findings with regard to traffic volume were the similarities in certain volume characteristics which were found to exist between the seven arterials studied. Ratios, in percentage form, of shorter peak period volumes to longer peak period volumes were computed, and comparisons between routes revealed surprising similarities. Similarities in the cumulative distribution curves of daily minute traffic volumes permitted devising a method for estimating per- centile minute volumes for any of the seven routes. The distribution of minute volumes, by lane, as related to total minute volume was investigated, and the equation for average minute volume in the middle lane as a function of the total minute volume for three lanes in one direction was formulated. Computations were made of approximate confidence intervals for this relationship. The variation of 15-min average lane speeds, by time of day, and the distribution of 1-min average lane speeds for the seven study locations were determined, and pertinent observations and comparisons were made. By combining lanes on the facilities and plotting the variation of 15-min average speeds, it was found that during the period from 11 a.m. to 3 p.m. the deviations of individual 15-min average speeds from 24-hr average speed were extremely small -smaller, in fact, than the normal accuracy of the speed detection instruments.
Abstract