Improving Truck Safety at Interchanges

DTFH61-88-R-00072This report offers highway engineers guidance in designing interchanges so as to reduce the likelihood of truck accidents on highway interchanges. This report summarizes research showing that the interaction between truck dynamics and interchange geometry can contribute to rollovers, jackknifes, and other loss-of-control accidents. Engineers can apply corrective actions to six specific ramp design features that were found to contribute to truck accidents: poor transitions to superelevation, abrupt changes in compound curves, short deceleration lanes preceding tight-radius exits, curbs placed on the outside of ramp curves, lowered friction levels on high speed ramps, and substantial downgrades leading to tight ramp curves. Countermeasures for these design problems include incorporating a greater safety margin into formulations for side friction factors, reviewing and modifying posted speed limits, improving curve condition and downgrade signs at interchanges, increasing deceleration lane length, overlaying curbs with wedges of pavement or eliminating curbs altogether, resurfacing ramps with high-friction overlays, and redesigning sites where accidents are common

Reducing Runaway Truck Accidents Through Weight-Based Advisory Speeds

DTFH61-88-R-00072Current developments in truck design may worsen the problem of runaway trucks. Trucks are becoming heavier, and the design of more aerodynamic cabs and the use of radial and smaller-diameter tires may increase the potential for brake failure on downgrades. This report gives State transportation officials an overview of the Grade Severity Rating System, a program to reduce runaway truck accidents through the use of weight-specific-speed (WSS) signs. The report contains adequate information for State transportation officials to decide whether they want to implement GSRS-WSS and also tells potential users where to get the additional information needed for actual implementation. The report summarizes the five steps required to implement WSS signing. The first step determines the magnitude of the runaway truck problem in a given State and identifies potential WSS sites. The second step analyzes the sites selected to determine percent and length of downgrade and truck braking length--the variables that determine brake temperature and hence safe speeds for different truck weight classes. In step three, analysts enter percent of grade and grade length or truck braking length into a computer program that yields advisory speeds for various truck weight classes. Step four converts the computer program output into the information that will actually be posted on WSS signs. Step five is actual installation of signs before and preferably along the downgrades selected for WSS. The report is based on the following studies: Feasibility of a Grade Severity Rating System, FHWA/RD-79/116, The Development and Evaluation of a Prototype Grade Severity Rating System, FHWA/RD-81/185, Field Test of the Grade Severity Rating System (GSRS), FHWA/RD-86/011, and Grade Severity Rating System (GSRS)--Users Manual, FHWA-IP-88-015

Reducing runaway truck accidents through weight-based advisory speeds. Summary report.

Federal Highway Administration, Office of Implementation, McLean, Va.Mode of access: Internet.Author corporate affiliation: Walcoff and Associates, Alexandria, Va.Report covers the period July 1988-Sept 1989Subject code: CGESubject code: DEFGSubject code: NOX*DOSubject code: NSGSubject code: PMVLSubject code: RCBD

Virulence of a Phosphoribosylaminoimidazole Carboxylase-Deficient Candida albicans Strain in an Immunosuppressed Murine Model of Systemic Candidiasis

The relative pathogenicities of three Candida albicans strains differing in the function of ADE2 (the gene encoding phosphoribosylaminoimidazole carboxylase) were evaluated in a murine candidiasis model. C. albicans strain CAI7 (ade2/ade2), previously constructed by site-specific recombination, was avirulent in immunosuppressed mice compared to the parent strain, CAF2-1, and a heterozygous ADE2/ade2 strain obtained by transforming CAI7 with a wild-type allele. The reduced virulence of CAI7 was correlated with the inability to proliferate in either synthetic medium or serum without the exogenous addition of >10 μg of adenine/ml. The loss of virulence upon site-specific disruption of the ade2 locus, and the restoration of wild-type virulence with the repair of just one ade2 allele, confirmed that the ADE2 gene and de novo purine biosynthesis were required for Candida pathogenicity. The potential of the phosphoribosylaminoimidazole carboxylase enzyme as a novel target for antifungal drug discovery is discussed

Intramolecular Charge-Assisted Hydrogen Bond Strength in Pseudochair Carboxyphosphate

Carboxyphosphate, a suspected intermediate in ATP-dependent carboxylases, has not been isolated nor observed directly by experiment. Consequently, little is known concerning its structure, stability, and ionization state. Recently, carboxyphosphate as either a monoanion or dianion has been shown computationally to adopt a novel pseudochair conformation featuring an intramolecular charge-assisted hydrogen bond (CAHB). In this work, additive and subtractive correction schemes to the commonly employed open–closed method are used to estimate the strength of the CAHB. Truhlar’s Minnesota M06-2X functional with Dunning’s aug-cc-pVTZ basis set has been used for geometry optimization, energy evaluation, and frequency analysis. The CHARMM force field has been used to approximate the Pauli repulsive terms in the closed and open forms of carboxyphosphate. From our additive correction scheme, differential Pauli repulsion contributions between the pseudochair (closed) and open conformations of carboxyphosphate are found to be significant in determining the CAHB strength. The additive correction modifies the CAHB prediction (Δ<i>E</i>_{closed–open}) of −14 kcal/mol for the monoanion and −12 kcal/mol for the dianion to −22.9 and −18.4 kcal/mol, respectively. Results from the subtractive technique reinforce those from our additive procedure, where the predicted CAHB strength ranges from −17.8 to −25.4 kcal/mol for the monoanion and from −15.7 to −20.9 kcal/mol for the dianion. Ultimately, we find that the CAHB in carboxyphosphate meets the criteria for short-strong hydrogen bonds. However, carboxyphosphate has a unique energy profile that does not result in the symmetric double-well behavior of low-barrier hydrogen bonds. These findings provide deeper insight into the pseudochair conformation of carboxyphosphate, and lead to an improved mechanistic understanding of this intermediate in ATP-dependent carboxylases