Impact of Specific Geometric Features on Truck Operations and Safety at Interchanges. Vol. I - Technical Report

1985Freitas, MichaelPDFTech ReportFHWA/RD-86/057DTFH61-82-C-00054Geometric designRoads--Interchanges and intersectionsExpress highwaysTrucks--Safety measuresUnited StatesUnited States. Federal Highway AdministrationErvin, R. D.Barnes, M.MacAdam, C.Scott, R.Freitas, MichaelUniversity of Michigan. Transportation Research InstituteUnited States. Federal Highway AdministrationFederal Highway AdministrationThe problem of truck loss of control accidents on interchange ramps is examined from the viewpoint of the suitability of highway geometric design, given the peculiar stability and control limitations of heavy duty trucks. Accident records were used to identify specific ramps which were over involved in jackknife, rollover, and run off road accidents. The ramp geometries were represented in a complex simulation of the dynamic behavior of representative tractor semitrailer combinations. The calculated responses of heavy vehicles on each ramp were studied to illustrate how highway design features may have influenced the known accident experience at the site. Results show that various aspects of the AASHTO policy on geometric design result in a very slim margin of safety for the operation of heavy trucks on exit ramps. Problem features included side friction factors, superelevation transitions, compound curves, deceleration lanes, ramp downgrades, curbs on curved ramps, and wet surface friction on high speed ramps. Potential countermeasures for the identified problems are suggested. Recommendations include a careful look at the prevalence of "problem ramps", nationally, initiation of efforts by State highway engineers to apply these findings to ramps having a known truck problem, and informing truck drivers of the situation involving slim safety margins.80