Enhanced air-coupled impact echo technique by phase analysis of signals from multiple sensors

This paper presents an air-coupled impact echo(IE)technique that relies on the phase spectrum of the collected data to find the frequencies corresponding to the reflections from delaminations.The proposed technique takes advantage of the fact that the IE compression wave is not a propagating wave,but it is the 1st order symmetrical(S1)mode Lamb wave at zero group velocity(S1-ZGV).Therefore,it searches the phase spectra of the data collected by multiple sensors to locate the frequency corresponding to the lowest phase difference.As a result,the technique reduces the effect of propagating waves,including the direct acoustic wave and ambient noise.It is named the Constant Phase IE(CPIE).The performance of the CPIE is experimentally compared with the regular amplitude spectrum-based IE technique and two other multisensor IE techniques.The CPIE shows a performance advantage,especially in a noisy environment.

Performance evaluation of the HCM 2010 platoon dispersion model under midblock pedestrian and truck traffic friction conditions

The urban street segment analysis chapter of the Highway Capacity Manual 2010 provides a methodology for evaluating automobile performance on street segments within an urban roadway network （TRB, 2010）. The methodology involves applying a platoon dispersion model to predict platoon arrival profiles at a downstream signalized intersection; using the predicted arrival flow profiles to compute the proportion of vehicle arrivals on green, and subsequently compute the control delay, average travel speed and level of service （LOS） of the segment. The predictive ability of the HCM 2010 platoon dispersion model has not been independently evaluated using field data. This paper, therefore, uses field data to evaluate the performance of the HCM 2010 platoon dispersion model under friction and no friction traffic conditions. The traffic friction conditions include pedestrian and vehicular interactions on urban collector street segments and the presence of trucks within the traffic stream on principal urban arterial segments. Based on the results obtained, the HCM 2010 platoon dispersion model performs relatively well in predicting platoon arrival profiles on urban street segments with no friction traffic conditions. The results, however, show the model＇s performance is limited on urban street segments with pedestrian and truck friction conditions.

Pedestrian walking speed at un-signalized midblock crosswalk and its impact on urban street segment performance

The Urban Street Segment Chapter of the Highway Capacity Manual(HCM)includes a methodology for evaluating the level of service urban street segments provide to automobile users.The methodology does not account for pedestrian activity at un-signalized midblock crosswalk on an urban street segment.Pedestrian activity at un-signalized midblock crosswalk on urban street segments causes friction conditions between automobiles and pedestrians.As a consequence,the average time it takes vehicles to travel along the segment is increased.Increasing segment running time decreases both the travel speed of automobiles and the level of service provided to automobile users.There is an inverse relationship between the delay incurred by interrupted vehicles and the speeds at which pedestrians walk while crossing at midblock.To account for this delay,there is a need to investigate pedestrian walking speeds at un-signalized midblock crosswalks.This study measured pedestrian walking speeds by age-group at two un-signalized midblock crosswalks on urban street segments.The first objective of this paper is to perform statistical analyses to examine the measured free-flow pedestrian walking speeds.The second objective is to demonstrate how the findings of this study can be incorporated into the Urban Street Segment Analysis Chapter of the HCM.Pedestrian walking speeds were recorded and analyzed for 2937 pedestrians.The results show teenagers walk at an average speed of 1.45 m/s,young adults walk at an average speed of 1.55 m/s,middle age pedestrians walk at a speed of 1.45 m/s,older pedestrians walk at speed of 1.09 m/s,and elderly or physically disabled pedestrians walk at a speed of 1.04 m/s.