Date of Award


Degree Type


Degree Name

Master of Science in Civil Engineering


Washkewicz College of Engineering

First Advisor

Jenkins, Jacqueline

Subject Headings

Civil Engineering


Freeway on-ramps are critical components of freeway systems since they control the entry of traffic to the mainline. According to the Highway Capacity Manual (HCM), a two-lane on-ramp configuration will achieve less turbulence than a similar one-lane on-ramp but little guidance on the desired lengths of the acceleration lanes or their effect on the operation of the influence area is provided. An experiment was designed to investigate the effect of the lengths of the acceleration lanes of isolated, two-lane on-ramps on the operation of the ramp influence area. The Highway Capacity Software (HCS) was used to calculate the density of the influence area corresponding to five length combinations for the first and second acceleration lanes, LA1 and LA2, keeping the effective length, L_Aeff constant. The analysis was carried out using two sets of volumes for the freeway, VF and ramp, VR. As expected, the density of the ramp influence area remained constant, for each volume set, illustrating that the HCM methodology is not sensitive to changes in the acceleration lane lengths making up L_Aeff. The experiment was repeated using the microscopic traffic simulation software, VISSIM. As expected, the two-way ANOVA results indicated the effect of the volume was significant ((p<0.001, α=0.05). As, LA1 decreased from 500ft to 100ft and LA2 increased from 500ft to 1300ft, the average density in the ramp influence area decreased when Vf=5000vph and Vr=1000vph. This effect was found to be significant (p=0.029, α=0.05) using a one-way ANOVA. However, the effect of the acceleration lane length was not significant (p=0.992, α=0.05) when VF=3500vph and VR=500vph. These results raise questions about the HCM equation for estimating the density of the influence area for two-lane on-ramps. Possible changes to the HCM equation are discussed.