Transport Research Laboratory Research Articles

Performance Evaluation of Full-Scale Sections of Asphalt Pavements in the State of Qatar

The population and economy in the State of Qatar have been increasing in the past 5 years. Accordingly, traffic loading has also increased rapidly, which affected the performance of existing roads and highways. This high traffic loading merits consideration of the design and construction of long-lasting pavements that require minimal maintenance. The Transport Research Laboratory (TRL) in collaboration with the Public Works Authority (PWA) of Qatar constructed a field experiment that consisted of six different pavement sections in order to investigate the influence of using different materials and asphalt mixture designs on performance. This paper presents a comprehensive study for the field evaluation of the performance of these trial sections. The evaluation involved the use of the falling weight deflectometer (FWD) and a vehicle equipped with instruments for measuring permanent deformation and cracking. These field measurements were complemented with laboratory measurements on field cores: the dynamic modulus, flow number, and semicircular bending tests. The results revealed that the increase in temperature between winter and summer in Qatar reduced the stiffness of asphalt mixtures by about 80%. The sections in which polymer-modified bitumen was used had the lowest temperature susceptibility. Moreover, the results showed that the bitumen and aggregate type significantly affected the stiffness and the trial sections’ resistance to rutting and fracture.

Safety assessment characteristics of pedestrian legform impactors in vehicle-front impact tests

This study investigated the characteristics of safety assessment results of front-area vehicle impact tests carried out using the Transport Research Laboratory (TRL) legform impactor and a flexible legform impactor (FLEX legform impactor). Different types of vehicles (sedan, sport utility vehicle, high-roof K-car, and light cargo van) were examined. The impact locations in the study were the center of the bumper and an extremely stiff structure of the bumper (i.e., in front of the side member) of each tested vehicle. The measured injury criteria were normalized by injury assessment reference values of each legform impactor. The test results for center and side-member impacts indicated that there were no significant differences in ligament injury assessments derived from the normalized knee ligament injury measures between the TRL legform impactor and the FLEX legform impactor. Evaluations made using the TRL legform impactor and the FLEX legform impactor are thus similar in the vehicle safety investigation for knee ligament injury. Vehicle-center impact test results revealed that the tibia fracture assessments derived from the normalized tibia fracture measures did not significantly differ between the TRL legform impactor and the FLEX legform impactor. However, for an impact against an extremely stiff structure, there was a difference in the tibia fracture assessment between the FLEX legform impactor and the TRL legform impactor owing to their different sensor types.

Robust design optimization of frontal structures for minimizing injury risks of Flex Pedestrian Legform Impactor

The Flexible Pedestrian Legform Impactor (Flex-PLI) consisting of a flexible femur and tibia will be tested for pedestrian protection by Euro NCAP within the next couple of years as a potential replacement for the Transport Research Laboratory (TRL) legform impactor. The injury risks that are measured when using Flex-PLI are the elongation of the anterior/posterior cruciate ligament (A/PCL), elongation of the medial collateral ligament (MCL), and tibia bending moment (TBM). In this study, we used a correlated computer-aided engineering (CAE) model to conduct a contribution analysis of each injury with regard to the changes in the location of the frontal structures based on the results of a design of experiments (DOE) and analysis of variance (ANOVA). The frontal structures that were selected as control factors were the energy absorber (EA), lower bumper stiffener (LBS), and hood angle. A kriging interpolation model was developed using the DOE results, and its results were compared with those of the CAE model. Furthermore, for robust design optimization, the speed and height of Flex-PLI were used as the noise factors. Finally, a robust design optimization was carried out using the optimal combination of the discrete control factors for minimizing MCL elongation.

Effect of humidity on dynamic characteristics of foam CF45 for the TRL pedestrian legform impactor

The improvement of computer simulation technology allows car designers to evaluate injury risks of newly designed bumpers using models of a car and the Transport Research Laboratory (TRL) legform impactor. Since the Confor™ foam type CF45 of the TRL legform impactor is not a non-ferrous material, the material's dynamic compression characteristics should be clarified for the development of a highly reliable TRL legform impactor model. The stress–strain characteristics of CF45 of varying thickness were investigated under dynamic compression conditions. The humidity conditions were set at RH30% and RH60%. The effect of humidity on the stress–strain characteristics of CF45 was clarified. We proposed a stress–strain curve for the TRL legform impactor model.

Capacity Analysis on Multi-Lane Roundabouts: An Evaluation With Highway Capacity Manual 2010 Capacity Model

In this study, capacity estimations with the incorporation of Highway Capacity Manual (HCM) 2010 method are evaluated. Parameter based sensitivity analysis on calculations with the new HCM formula and a comparative evaluation of the new methodology with two most common capacity analysis methods, i.e., the method of critical gap acceptance and the method of regression analysis, are performed. Maximum and minimum headway intervals of follow up time and critical gap parameters are alternated within the sensitivity analysis. The Transport Research Laboratory formula for regression and Australian formula for gap acceptance method are considered in comparison. Relative comparisons of predictions on capacity by HCM2010 method, regression analysis and gap acceptance method are presented considering field data obtained by observations at two roundabouts in Izmir, Turkey. The results of the study show that the HCM2010 formula led to lower capacity estimates than regression analysis and higher estimates than the gap acceptance method. Regarding the real capacity observations under high circulating flow-rates the HCM2010 method yielded to more appropriate results than the regression method. In addition to comparisons, studies on the sensitivity analysis show that entry capacity estimates possess sharper changes as smaller follow up headways are accepted.

Geogrid-Reinforced Low-Volume Flexible Pavements: Pavement Response and Geogrid Optimal Location

AbstractThis article discusses the geogrid’s potential to reduce granular base shear flow. Researchers have previously acknowledged the geogrid’s potential to enhance the performance of roadways, but this study goes further to (1) investigate the effectiveness of a geogrid when it is used to reinforce low-volume conventional flexible pavements constructed on low-strength subgrade and (2) to specify the optimal location for installing a geogrid in a low-volume pavement system. To quantify the effectiveness of a geogrid in flexible pavements, nine low-volume pavement design sections were constructed at the University of Illinois Advanced Transportation Research and Engineering Laboratory (ATREL). A total of 173 instruments were embedded in the pavement layers during construction to measure pavement responses. The test sections were then loaded using an accelerated loading system, and the pavements’ responses to conventional dual-tire loading were measured. This paper reveals how various pavement designs res...

Comparison of Reponses of the Flex-PLI and TRL Legform Impactors in Pedestrian Tests

Injuries to the lower extremities are one of the major issues in vehicle-to-pedestrian collisions. To evaluate pedestrian lower extremity protection, the Transport Research Laboratory (TRL) legform impact tests have been conducted according to the specifications in the EU directive. The TRL legform impactor consists of a tibia and a femur steel shaft connected by deformable knee bars. A Flexible Pedestrian Leg-form Impactor (Flex-PLI), which has flexible femur and tibia, is examined in the Global Technical Regulation (GTR). Previous studies compared the responses of both impactors; however, the relation between the tibia acceleration in the TRL legform impactor and the maximum bending moment in the Flex-PLI (both injury measures are for the tibia fracture) is not understood sufficiently. In this study, using finite element (FE) analyses, the injury measures of the TRL legform and the Flex-PLI were compared with those of the human FE model in impact with a simple large car model to identify which injury measures of the two impactors are reasonable to predict injury risk to pedestrian lower extremity. The rigid body model was used to gain a theoretical understanding of the injury measures of the impactors. Based on the equations of motion of the rigid body model, physical parameters were identified that relate with the injury measures. The tibia acceleration relates with the bumper force and the spoiler force. The bending moment depends on the equation that is expressed by the force and distance of the bumper and the spoiler energy absorber. Therefore, the tibia acceleration and the bending moment are different design parameters. The knee bending angle depends on the moment around the tibia center of gravity. Analyses of the TRL legform, Flex-PLI and human FE models were conducted; and it was shown that the injury measures in the FE models were affected significantly by the physical parameters determined in the rigid body model. The responses of the TRL legform, the Flex-PLI, and human FE models were compared with changing vehicle parameters. The trend was comparable for the three models. However, when the bumper energy absorber was soft and its bottoming-out occurred, the tibia acceleration in the TRL legform increased sharply, whereas the bending moment in the Flex-PLI did not increase. In the human FE model, when the bumper energy absorber bottomed out, the stress of the tibia that made contact with the bumper energy absorber was still small. As far as changing parameters of the large car in the present study, the responses of the Flex-PLI are more comparable with the human FE model than those of the TRL legform impactor; and it is likely that the Flex-PLI can predict injury risk more reasonably than the TRL legform impactor. Language: en

Effect of humidity on pedestrian legform impactor-to-car bumper impact test results

The effect of humidity on the measured injury criteria of the Transport Research Laboratory (TRL) legform impactor in the bumper impact test was evaluated. The following investigations were conducted in two different humidity conditions – 30% and 60% relative humidity (RH) environments. First, dynamic certification tests were conducted. Second, legform impactor-to-bumper impact tests using two sedan cars were conducted to capture the trend in results for different cars. Third, to clarify the mechanism of the effect of humidity on the measured criteria, numerical simulations were conducted using newly developed finite element models of the dynamic certification test and a bumper impact test for one sedan car. In the legform impactor-to-bumper impact tests and the numerical simulation, the measured injury criteria used were the same for the two humidity conditions. The results indicate that the humidity condition does not affect any injury measure in the legform impactor-to-bumper impact test. The numerical simulation elucidated the mechanism of the effect of humidity on the measured criteria of the legform impactor.

J021022 人体FEMを使った歩行者保護用下肢傷害評価手法(Flex-PLI)

The Flexible Pedestrian Legform Impactor (Flex-PLI), is developed by Japan Automobile Manufacturers Association (JAMA) and Japan Automobile Research Institute (JARI) to improve bio-fidelity of the ongoing legform impactor developed by TRL (Transport Research Laboratory). This paper presents simulation results of Flex-PLI shots to SUV (Sport-Utility Vehicle) and examines its kinematics. The results are compared with those of Human FE (Finite Element) model.

A comparison of the use of the cell transmission and platoon dispersion models in TRANSYT 13

The TRANSYT software, developed by the UK's Transport Research Laboratory (TRL), has been used for optimising signal timings in signalised networks for over 40 years. It consists of a deterministic, macroscopic traffic model that evaluates the performance index (PI) for any given set of timings x and an optimiser that seeks to minimise the PI and hence find the optimal timings x*. The conventional platoon dispersion model in TRANSYT has the well-known weakness of treating queues as if they stacked vertically at the stop-line, and hence does not model ‘blocking back’. However, the latest version, TRANSYT-13, offers an alternative form of traffic model, the cell transmission model, which models the spatial extent of queues, and should be more accurate, especially in networks with closely spaced intersections. The paper investigates the sensitivity of the resulting optimal signal timings to the choice of traffic model, through application of TRANSYT-13 to a 6-arm signalised motorway roundabout. The objective is to measure the benefit from using the improved traffic model.

Comparison of Structural Capacity of Hot Mix Asphalt (HMA) Pavement Designs (AASHTO & TRL RN-31 )

The primary objective of this research is to identify the proper design guidelines in terms of structural capacity, which enables to last longer life span without any major failure. Inducing very high stress on pavement is one of the major reasons for structural failure. American Association of State Highway and Testing Officials (AASHTO) and the Transport Research Laboratory Road Note 31 (TRL RN-31) are the widely used pavement design guidelines by many road agencies. Hence, this study intends to compare and contrast AASHTO (1994) and TRL RN-31. AASHTO method involve with the complicated empirical equation 3 in appendix which has to be solved by iteration method to obtain the required structural capacity for given conditions. So, computer program was developed using JAVA to solve AASHTO equation. RN-31 and AASHTO methods have been directly compared for a range of subgrade California Bearing Ratio (CBR) and traffic levels. Model pavements were constructed to evaluate the performance of the pavement for static load and field collected data were used to verify the Finite Element Model (FEM). The verified models were used to evaluate the structural performance of pavements. The main advantage of this review on flexible pavement design guidelines is that the pavement which provide higher structural capacity can be simply identified and constructed, so that, it can reduce the overall cost and provide good platform to the users.

Development of a Calibration Procedure for the U.K. Highways Agency Traffic-Speed Deflectometer

One of the headline objectives of the U.K. Highways Agency (HA) is to reduce congestion and improve road safety while undertaking necessary highway maintenance. To this end, HA has invested significant resources in developing an appropriate technology to collect road condition and structural data at traffic speeds. This is reflected in the recent procurement for HA of a prototype traffic-speed deflectometer (TSD). The machine, originally developed by Greenwood Engineering A/S of Denmark, exploits the Doppler effect by using lasers to measure pavement deflection velocities under the loaded wheel of a truck. As part of a research program at the U.K. Transport Research Laboratory, the TSD is being developed to undertake structural surveys at traffic speeds. This paper describes the operation of the TSD and continues with a discussion of one of the most challenging aspects of the research program: the development of a calibration procedure. The proposed procedure compares the response of a particular section of road to the TSD, as recorded by an accelerometer embedded in the road pavement, with that recorded by the Doppler lasers on the TSD.

Improving the Design of Low Volume Sealed Roads in Tanzania

The main objective of the study was to identify appropriate road designs for Low Volume Sealed Roads (LVSRs) with the aim of improving the design of such roads in Tanzania. The study was conducted in Dar es Salaam and Morogoro regions in Tanzania where data for LVSRs were collected from primary and secondary sources in the two regions. The study found that by using an improved pavement design method specifically meant for LVSRs results in cost savings for LVSRs of up to 51% compared with the conventional method of pavement design in Tanzania. The study recommends that the pavement design method for lightly trafficked sealed roads in southern Africa developed by Transport Research Laboratory, which was found to be most cost-effective, be used to design (or develop a procedure for design of) LVSRs in Tanzania and that the roads be preferably sealed with Otta seal or Surface dressing. The study also recommends that LVSRs in Tanzania be defined by a maximum traffic volume of 400 vpd.

Generalised collapse analysis of concrete bridges

An automated yield-line analysis technique for reinforced concrete slab structures has been developed at the University of Cambridge and implemented in a computer program called COBRAS for use in assessing the ultimate flexural strength of concrete bridges. The program employs recent developments in solid modelling theory to create a three-dimensional model or ‘picture’ of a bridge and all its components within the computer. This model is built up from a number of separate layers of polygonal regions, each of which represents the plan location within the bridge of a particular structural feature. In combination, these polygons provide all the information necessary to describe the structural parameters of the material components and dimensions of the bridge, the external loading acting on the bridge and the geometric information required for the collapse mechanism analysis. This enables realistic bridge and load configurations to be analysed rigorously and very rapidly. An extensive theoretical and experimental validation programme was undertaken in collaboration with the Transport Research Laboratory and the program has been adopted widely by bridge engineers in the UK and also abroad, primarily for use in assessing the load capacity of short-span reinforced-concrete slab bridges.

Fit for purpose: evaluating walkability

This paper describes the challenges associated with assessing the quality of pedestrian networks and facilities, in particular the diverse nature of pedestrians and their sensitivity to subjective influences. It describes the ways in which those challenges were addressed during development of the pedestrian environment review system (PERS) by the Transport Research Laboratory (TRL). The paper describes PERS and gives examples of its application and use to conduct pedestrian network quality analysis. The benefits and limitations of the approach and lessons learnt in applying pedestrian reviews are discussed in a number of contexts. The paper concludes that the diversity of pedestrian capabilities and purposes in the public realm requires that subjective factors be incorporated into a review system; this, however, poses substantial difficulties for an objective and replicable review system.

Assessing methodologies for calculating road traffic noise levels in Ireland – Converting CRTN indicators to the EU indicators ( Lden, Lnight)

To comply with the EU Noise Directive 2002/49/EC, Member States are required to produce strategic noise maps for designated areas, including mapping road traffic noise from major roads. These maps must be presented using the EU indicators L den and L night. However, the most common noise indicator used in Ireland at present is the L A10,18h indicator arising from the use of the Calculation of Road Traffic Noise (CRTN) prediction method. Therefore, a relationship needs to be established between L A10,18h and L den and L night, separately. In addition to noise mapping these indicators are used for noise abatement purposes, so the proposed relationship must be accurate and robust. In 2002, the UK’s Transport Research Laboratory (TRL) published a paper describing mathematical procedures that could be used to convert values of L A10 to L den and L night. These procedures were then adopted for use in Ireland. This paper examines the suitability of the TRL conversion methods 1 and 3 for use under Irish road conditions. Method 2 was not considered in this study, as it was a methodology not applicable in an Irish scenario. Studies concluded that where hourly traffic data are available, the conversion methodology outlined in TRL Method 1 is robust and reproducible. However, in the absence of hourly traffic data where daily traffic counts are used, the relevant conversion procedures produce variable results for both L den and L night when applied to Irish road conditions. To reduce the variability, new conversion procedures were developed, specifically for Irish road conditions.

3215 歩行者脚部インパクタを用いた乗用車衝撃試験における湿度条件の検討(OS5-3 安全・安心・防災の技術,OS5 安全・安心・防災・環境負荷低減,オーガナイズド・セッション)

Humidity reportedly causes a scatter of maximum acceleration in a dynamic certification test using a Transport Research Laboratory (TRL) legform impcator according to the European Enhanced Vehicle-safety Committee /WG17 method. The possibility was considered that humidity might affect the injury criteria for the TRL legform impactor to bumper impact test. To clarify the differences in the maximum acceleration of the impactor in different humidity conditions, a dynamic certification test and the legform impactor to bumper impact test were conducted in two different humidity conditions (30%RH and 60%RH). In the dynamic certification test, the maximum acceleration and shear displacement used were not the same in the two humidity conditions. In the legform impactor to bumper impact test, the measured injury criteria used were the same in the two humidity conditions. The results indicated that the humidity condition affect two of three injury criteria in the dynamic certification test. On the other hand, the results also indicated that the humidity condition does not affect all injury criteria in the legform impactor to bumper impact test.

Pedestrian leg protection performance in current vehicle design in an event of vehicle-to-pedestrian accident

Accident data show that leg injuries are the most common injuries in non-fatal pedestrian traffic accidents. The investigation reported in this article focuses on evaluating the pedestrian protection provided by the front bumpers of three different types of current Japanese vehicle: sedan, sport utility vehicle and K-car (engine displacement of 660 cc or less). The investigation used the Transport Research Laboratory (TRL) legform impactor. The protection performance related to knee ligament injury and tibia fracture greatly depended on the vehicle's frontal shape and the stiffness of both the bumper and the bonnet or grill of the vehicle. The study showed that for the three vehicles tested, the pedestrian leg protection performance at the bumper centre location was excellent but the performance of the bumper in front of the longitudinal members was poor.

Work-related road safety

This commentary considers work-related road safety and strategies that can be used to reduce work-related traffic accidents, which account for between 25% and 33% of all serious and fatal road accidents. The author first reports some of the statistics found by the Royal Society for the Prevention of Accidents (RoSPA), the Dykes Report of 2001 about the high risks faced by people on the road for work purposes, and studies from the Transport Research Laboratory (TRL). The author then considers ways that employers could take work-related road safety more seriously, including vehicle selection, scheduling, training courses, and the use of information from the organizations in the Occupational Road Safety Alliance. The author concludes by calling for additional government resources to tackle this problem of work-related road safety.

Spinal injuries following major motor vehicle crashes

Introduction: The epidemiology of spinal injuries following serious motor vehicle accidents is not well known. In this study, we describe the mechanisms of injury, patient characteristics and spinal injury distribution and severity. We also aim to describe the associated injuries in these patients. Methods: Data was extracted from the Co-operative Crash Injury Study (CCIS) database, maintained by Transport Research Laboratory, UK. From June 1998 to January 2006, patients who were prospectively coded as having spinal injuries were identified. Injury severity of single injuries was coded using the Abbreviated Injury Severity (AIS) score, and overall severity was calculated for each occupant using the Injury Severity Score (ISS). We excluded all AIS 1 (minor) injuries from the analysis. Results: During the study period, 4405 occupants were identified as having sustained a spinal injury. After excluding AIS 1 injuries, there were 457 occupants left. Drivers (63.7%) and young males in the age group 18-34 (26.3%) were the dominant group. The cervical spine (53.2%) was the spinal region most commonly involved and also accounted for most of the severe AIS 5 and 6 spinal injuries. The thoracic spine (30.9%) was the next most involved followed by the lumbar spine (24.7%). There was a high overall mortality (41.6%), and this was most marked amongst the over 65 age group (60%). The majority of occupants had a significant non-spinal AIS =2 injury (89.5%). Discussion: The cervical spine is the most vulnerable part of the vertebral column during MVCs. Overall mortality, especially in the elderly is high, and prompt identification of associated injuries is important. Further work is needed to study the outcome of patients sustaining spinal injuries as part of major trauma, especially in the elderly.