Time-lapse, aerial photographs were taken at 29 entrance ramps in seven cities across the country and data from 23 of these entrance ramps are presented. The ramps had a wide range of geometrics, i.e., acceleration lane lengths 240 ft to 1,500 ft and convergence angles between 1 and 14 deg. The geometric elements for which the operational effects were most carefully evaluated are acceleration lane length, angle of convergence and ramp grade. Operational characteristics examined were speed of ramp vehicles at the ramp nose and at the merge point, change of speed of ramp vehicles between the ramp nose and the merge point, the relative speeds of vehicles at the ramp nose and at the merge point, the accepted gap number and the distribution of points of entry onto the freeway. All of these analyses were made during periods in which the freeway operating speed was in excess of 40 mph. Each of the variables, acceleration lane length, angle of convergence and ramp grade, were found to have a great effect on the merging operation. General conclusions regarding entrance ramp design are presented. /author/.
Abstract