A CASE STUDY OF TRUCK MERGING OPERATIONS AT SELECTED FREEWAY ON-RAMP LOCATIONS IN CALIFORNIA

This report provides an evaluation of truck merging operations for selected freeway on-ramp locations where there are significant truck volumes. Data regarding vehicle merge locations, speeds, traffic volumes, and accidents are included in this report. There is an auxiliary lane approximately 2152 ft (655.9 m) long at one of the rural locations (Stanislaus County, Route 5, Ingram Creek Road Interchange, postmile 23.0, northbound on-ramp). The auxiliary lane was adequate for merging and was used by most vehicles. The fatal and injury accident rate for the merge area at this location was higher than the expected accident rate. This difference was not statistically significant. The fatal and injury accident rate for the merge area at the other rural location (San Bernardino County, Route 15, Lenwood Road Interchange, postmile 68.8, northbound on-ramp) was higher than the expected accident rate. This difference was statistically significant. It should be noted that an auxiliary lane is currently being proposed at this location. Vehicle merge data were not summarized for this location. At the two suburban locations (San Bernardino County, Route 10, postmile 13.2, Cherry Avenue Interchange, westbound and eastbound on-ramps) most of the merging by cars and by truck combinations occurred within intervals of only about 200 ft to 350 ft (61.0 m to 106.7 m). The fatal and injury accident rates for the merge areas at these locations were less than the expected accident rates. The annual average daily traffic and travel for the two rural locations were less than those for the suburban locations. Each of the four freeway on-ramp locations evaluated in this report has its unique set of characteristics in terms of traffic volumes and geometric design, which might influence truck merging operations. Therefore, the information contained in this report would be helpful for planning and designing freeway on-ramp merge areas with similar characteristics.