California Department of Transportation

About: California Department of Transportation is a government organization based out in Sacramento, California, United States. It is known for research contribution in the topics: Poison control & Seismic analysis. The organization has 308 authors who have published 389 publications receiving 12623 citations. The organization is also known as: Caltrans & Bureau of Highways.

Vehicle speed and acceleration profile study for metered on-ramps in California

Abstract: Ramp metering has been proven as an effective freeway-management strategy; however, one of the critical challenges in design and operation of ramp metering is the lack of up-to-date design guidance for acceleration lanes. This paper aims to investigate the actual acceleration characteristics for metered on-ramps with various geometric features and also figure out speed profiles to guide the design of acceleration-lane length. A piecewise-constant acceleration model, which assumes vehicles making uniformly accelerated motion within each short space or time interval, was employed to model vehicle acceleration characteristics. The approach of using distance versus speed profiles for acceleration-length design was also introduced. RESULTS show that acceleration rate at metered on-ramps is not constant; vehicles usually accelerate at a higher acceleration rate when speed is lower and vice versa. It was observed that taper ramps usually produce higher acceleration rates than ramps with an auxiliary lane, and existing acceleration length would also affect drivers' acceleration behavior. Finally, this study pointed out that the acceleration performance data documented in the AASHTO Green Book, which are now widely employed by several state DOTs in the United States as acceleration length design guidance for metered on-ramps, is approximately 1.7 times greater than the value measured at typical taper-type metered on-ramp in California. Language: en

Diagnosis of roller bearing defects using neural networks

Abstract: A new approach for the diagnosis of bearing defects has been utilised. Artificial neural networks (ANN) were employed for the diagnosis of various kinds of bearing defects. The features selected for this purpose were: the average of the top five values of amplitude in the high-frequency region (5 kHz-22 kHz), the peak value of the amplitude in the high-frequency region, the average of the top five values in the prime spike region (340 Hz-3262 Hz), the autocorrelation function in the prime spike region, the autocorrelation function in the high-frequency region, and the cepstrum function in the high-frequency region.

Structural characterization of modern highway overcrossings--case study

Abstract: This paper revisits the mechanical characterization of the main substructure elements of highway overcrossings in an effort to build a more balanced methodology to compute earthquake response of seismically protected bridges accounting for the effects of soil-structure interaction. Various macroscopic constitutive laws that are well known in literature are summarized and synthesized in a way that can be incorporated in reduced-order stick models used in practice. Here, the authors discuss the required sophistication level of the proposed macroscopic constitutive laws in order to capture the leading mechanical behavior of each substructural element without adding unnecessary complications when incorporated in a stick model idealization of the bridge.