Transport Research Laboratory Research Articles

Structural model performance and reinforced pavement technology in unstable location in the south of the Republic of Benin (West Africa)

The main cities in West Africa have been characterized by the development of infrastructure in past decade. This paper examined the performance of the soil and of pavement in Benin (West Africa). In this research, four objectives have been adopted in-depth on the performance characteristics of West African soil and aim to (i) accessing characteristics of soil types in the region; (ii) assessing the performance of these soils with 3% of lime, with the combination of 3% lime and 3% cement; (iii) using geogrid to evaluate the performance of pavement on clayey soil; (iv) proposing a new pavement model strategy considering economic aspects of construction. The methods used to examine these objectives are experimental tests according to standard French test. Design of flexible pavement is largely based on empirical methods according to the transport research laboratory (TRL) Note 31 with WinJulea software and compared with a designed and evaluated pavement structure adopting the center experimental of building and public works (CEBTP) method. In addition, the research quantified the percentage of biaxial geogrid impacting the performance of pavement in a diminishing perspective. Flexible pavements (with and without geogrids) were built and subjected to 127.49 ​kN load applications. This paper firstly reveals the unstable and stable areas in southern Benin (West Africa) with the presence of clay soil, and secondly reveals that the use of 3% lime and the combination of 3% lime and 3% cement are limited in subgrade. In addition, the TRL Note 31 with WinJulea software is more economical while the one of CEBTP highly performs. More so, the paper confirms that the use of biaxial geogrid reinforcement in pavement structures highly reduces the construction cost. As conclusion, firstly, the pavement made from the recycled asphalt pavement materials with biaxial geogrid in subgrade is the best in the clayey area.

Estimation of PCU Values for Urban Roads by Considering the Effect of Signalized Intersections under Mixed Traffic Conditions

Along with multiple classes of vehicles, frequent signalized intersections on the urban roads and the platoons thus created add complexity to the estimation of Passenger Car Units (PCU). Under such scenarios of interrupted traffic, a new approach based on platoon movement of vehicles is introduced for the realistic estimation of PCU values for urban roads by incorporating the appropriate vehicle behavior and interactions. The PCU values were derived by finding the trade-off between the speed reduction caused by the flow of passenger cars and other vehicle classes, as per the given definition by Transport Research Laboratory (TRL). However, the speed-flow, as well as the speed-density relations, were analyzed and found that later is preferred for the realistic estimation of PCUs for urban roads. The speed reduction is modeled using multiple linear regression with field data collected from typical urban roads characterized by platoon flow in Mumbai city (India).

Laboratory evaluation of an indigenous developed light weight deflectometer as a quality control tool for pavement construction

The mechanistic empirical pavement design concepts are largely based on the theory of elastic layers, and the design is assessed with the characterization of materials used in pavement construction. The present density-based quality assurance (QA) apparatus and its procedures are not effective in measuring the resilient modulus of compacted pavement layers. However, the use of high-cost field apparatus such as nuclear density gauges (NDG) is also encouraging the search for an alternative procedure. This article aims at the measurement of pavement surface modulus directly in the field using a low-cost laboratory developed Indigenous Light Weight Deflectometer (ILWD). The developed ILWDs will be employed for pavement construction QA for interpreting the stiffness of compacted pavement layers. The study was performed on the National Highway-161 in Sivampet, Sangareddy district, Telangana state. The laboratory developed ILWD was validated using the available Light Weight Deflectometer (LWD), Dynatest make, and layer modulus was also computed using a Dynamic Cone Penetrometer (DCP). The DCP was also fabricated in the laboratory as per the Transportation Research Laboratory (TRL), UK. The ILWD and DCP were used to ensure the stiffness characteristics like elastic and dynamic modulus. The field and lab test results indicate that the calculated elastic modulus and stiffness characteristics are close to each other layer moduli for the different pavement layers considered in the study, like sub-grade and granular sub-base (GSB). It is also observed that the test results from the field and laboratory have a good measure of statical correlation among the different stiffness values, and hence the developed ILWD is suitable for pavement compacted layer investigation as quality control.

Chain Reaction

Paul Campion, CEO of the UK’s Transport Research Laboratory (TRL), is pushing for more pedal power and a complete rethink on housing to help deliver a brighter tomorrow.

Geotechnical Characterization of the Subgrade on Some Rural Roads in Cross River State, Nigeria and the Influence of Geology

The subgrades of three different rural roads alignment were investigated with the aim to determine their geotechnical properties. The three roads are on two different geologic terrains. Two of the roads, the 18 km Yahe-Waniye-Wanakom road and the 6 km Okpoma-Okuku road are on Cretaceous sediments terrain, while the 8 km Ugboro-Imaje-Okuku road is on the Basement Complex terrain. Based on American Association of Highways and Transportation Officials (AASHTO) most of the soils classify as A-2-4, A-2-6 on the first two roads with A-7-5, A-7-6 soils interspersed between the A-2-4 soils. The A-2-4, A-2-6 soils were also encountered on the only alignment on the basement complex, but the A-7 group of soils were not encountered on this alignment. Based on The Transport Research Laboratory Road Note 31, subgrade quality on all the three alignments is classed into ‘S4 to S6’ subgrade class. In this classification scheme ‘S6’ is the subgrade of the highest quality.

Performance assessment and optimal design of hybrid material bumper for pedestrian lower extremity protection

Lower extremity injuries have exhibited a great proportion in pedestrian-vehicle accidents. This study aims to assess the performance of an innovative aluminum-steel hybrid material bumper for pedestrian lower extremity protection. Finite element (FE) models of the hybrid bumper and its two single-material counterparts were built, validated, and integrated into an automotive front-end structure. The Transport Research Laboratory (TRL) legform model was used to obtain values of the lower extremity injury indicators including the knee-bending angle α, the knee-shearing displacement Disp, and the tibia acceleration Acc, upon impacting on the three types of bumpers. Numerical results showed that the aluminum and the hybrid bumpers result in much less pedestrian lower extremity injuries than the steel bumper due to the lower stiffness and strength of the constitutive material. Besides, the hybrid bumper is superior to its homogeneous counterparts as to the requirements for both pedestrian protection at low-speed and load transfer at high-speed crashes. Moreover, multi-objective optimization designs (MOD) of the three bumpers were performed to minimize the pedestrian's lower extremity injuries, by means of the non-dominated Sorting Genetic Algorithm (NSGA-II) and the radial basis function (RBF) meta-models. The optimal results confirmed the greatest potential of the hybrid bumper for pedestrian lower extremity protection. By virtue of the entropy weight method to determine the weighting factor of each injury indicator, Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) was used to sort the obtained Pareto designs and to select the comprehensive optimal bumpers. The TOPSIS optimum of the hybrid bumper is much closer to the ‘utopian point’, showing again its advantages over the homogeneous counterparts for pedestrian lower extremity protection in pedestrian-vehicle accidents.

DESIGN OF FLEXIBLE PAVEMENT USING MARBLE DUST IN SUBGRADE SOIL

Harnessing of industrial waste for improvement of soils is economical and efficient. It helps in enhancing the soil properties and overcoming the disposal problem. Therefore, it is essential to understand the properties of these wastes in order to understand their performance level. In this study, waste marble dust was added to stabilize the soil which was collected from Rajpura Punjab. The various index properties liquid limit, plastic limit was studied by adding Marble dust 10%,15%,20% and 25% by weight of soil. Similarly, California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS) was calculated at maximum dry density obtained from compaction test. It was observed that based on tests that 20% of waste marble dust was optimum for strengthening of the parent soil. Resilient Modulus was calculated afterwards for the subgrade using models specified by Heukelom and Klomp, Thompson and Robnett, Transport and Road Research Laboratory, Erdem Coleri. Based on the results obtained, pavement thickness was determined for designing flexible pavement section as per IRC 37-2012 using IITPAVE. Design was done considering the horizontal tensile strain and vertical compressive strain at the bottom of bituminous base and at top of subgrade, responsible for fatigue and rutting of pavements.

Case study of construction quality control monitoring and strength evaluation of a lateritic pavement using the dynamic cone penetrometer

In this study, the quality and strength of unstabilized lateritic pavement layers of a 14 km single carriageway road under construction in Minna, Nigeria were measured and monitored by the Dynamic Cone Penetrometer (DCP) test in conjunction with standard laboratory testing of bulk and cored samples taken from designated sections. Atterberg’s limit tests revealed high liquid limits as well as plasticity index values at some sections in the sub-base layer. The dynamic cone penetrometer index (DCPI) values for the subgrade layer ranged from 3 mm/blow to 10 mm/blow whereas, DCPI values for the sub-base layer were observed to remain within a range of 5 mm/blow to 16 mm/blow. It was also found that good correlation similar to those developed by other researchers exists between CBR and DCPI values. However, comparison between the correlations by Transport Research Laboratory (TRL) and the one developed in this study showed that for both subgrade and sub-base layers, the new equation predicts slightly lower CBR than the TRL model. From the laboratory evaluation of soil samples, the subgrade CBR values ranged from 27 to 74% which qualify as good to excellent subgrade materials whereas the sub-base CBR varied from 15 to 50% and are rated as poor to good sub-base.

Analysis of past and future continental crash mortality rates employing long-term data

ABSTRACTThe global and continental crash death rate trends, adjusted for under-reporting, death definition, and missing data, are analyzed, modelled, and compared with international findings considering data for 215 countries for 35 years. Although global reported mortality rates required 25% to 44% adjustments, that estimated by World Health Organization (WHO) and World Bank showed far greater rates. The model developed for global mortality rates per population though indicates a peak threshold, the current rate is expected to continue for some years before descending. In contradiction with WHO, Transport Research Laboratory (TRL), and World Bank (WB), the model indicates a drop of 22% in mortality rate by 2025. The rate for Europe, Oceania, and Asia drop to one eighth, one half, and one sixth, respectively. The rates for Africa doesn't change, and that for South America increases by 15%. The current global mortality per 10,000 vehicles drops exponentially by 38% toward 2025. The mortality rate per 10,000 vehicles for the various continents are expected to drop by 34% to 68%. The earlier rates showed a much faster drop than that per population. The observant reason could be the faster vehicle growth compared with population. The findings call for extensive traffic safety plans and tense implementation efforts in Africa, South America, and Asia to have faster global descending trends in mortality rates. More research that considers under-reporting of fatalities is necessary.

Simulation analysis of traffic signal control and transit signal priority strategies under Arterial Coordination Conditions

This paper presents the findings of a simulation study evaluating the potential benefits of implementing transit signal priority (TSP) combined with arterial signal coordination for an isolated intersection. Traffic signal coordination is usually implemented along corridors with bus lanes. Active transit signal priority (active TSP) is a traffic-responsive control that prioritizes transit vehicles at signalized intersections. Thus, implementing active TSP under a stable cycle length is necessary to meet the relative demand of the non-priority phase and to maintain system stability. A real key intersection on an artery is taken as the object, and TSP controlling logics with specific restrictions are realized by using the VISSIM vehicle actuated programming module. Simulation analysis reveals the effect of TSP strategies with flow variation on the optimal cycle, and also identifies a reasonable method for selecting the gap time and initial green time of the priority phase. Results show that under special flow combination, increasing the cycle time generated by the traditional transportation and road research laboratory approach can give rise to additional benefits. The volume influences both the gap time and initial green time of the TSP phase. Moreover, the efficiency of red truncation is slightly better than that of the green extension strategy.

Optimization of traffic signal parameters based on distribution of link travel time

In order to make full use of digital data, such as data extracted from electronic police video systems, and optimize intersection signal parameters, the theoretical distribution of the vehicle’s road travel time must first be determined. The intersection signal cycle and the green splits were optimized simultaneously, and the system total travel time was selected as the optimization goal. The distribution of the vehicle’s link travel time is the combined results of the flow composition, road marking, the form of control, and the driver’s driving habits. The method proposed has 15% lower system total stop delay and fewer total stops than the method of TRRL (Transport and Road Research Laboratory) in England and the method of ARRB (Australian Road Research Board) in Australia. This method can save 0.5% total travel time and will be easier to understand and test, which establishes a causal relationship between optimal results and specific forms of road segment management, such as speed limits.

Novel Area Occupancy–Based Method for Passenger Car Unit Estimation on Multilane Urban Roads Under Heterogeneous Traffic Scenario

This research was aimed at developing an area occupancy–based method for estimating passenger car unit (PCU) values for vehicle categories under heterogeneous traffic conditions on multilane urban roads for a wide range of traffic flow levels. First, PCU values of vehicle categories were determined according to the Transport and Road Research Laboratory definition and replaced the commonly considered measure of performance speed with area occupancy using simulation. The PCU values obtained were found to be significantly different for different volume-to-capacity ratios; this result shows that the PCU value is dynamic in nature. While the dynamic nature of PCU values is well appreciated, practitioners may prefer a single set of optimized PCU values (unique for each vehicle category). Hence, a new method with a matrix solution was proposed to estimate the optimized or unique set of PCU values with area occupancy as the performance measure. To check the credibility of the proposed method, the estimated PCU values were compared from existing guidelines regulated by the Indian Roads Congress (IRC) and values estimated with the widely accepted dynamic PCU concept of speed–area ratio. Results show that the PCU values suggested by IRC and the dynamic PCU concept using the speed–area ratio underestimate and overestimate the flows, respectively, at different traffic volumes. However, the values obtained with the area-occupancy concept were found to be consistent with the traffic flow in a cars-only traffic situation at different flow conditions. The derived set of optimized PCU values proposed can be useful for traffic engineers, researchers, and practitioners for capacity and level-of-service analysis under heterogeneous traffic conditions.

Assessment of the impact speed and angle conditions for the EN1317 barrier tests

ABSTRACTRoadside safety barriers designs are tested with passenger cars in Europe using standard EN1317 in which the impact angle for normal, high and very high containment level tests is 20°. In comparison to EN1317, the US standard MASH has higher impact angles for cars and pickups (25°) and different vehicle masses. Studies in Europe (RISER) and the US have shown values for the 90th percentile impact angle of 30°–34°. Thus, the limited evidence available suggests that the 20° angle applied in EN 1317 may be too low.The first goal of this paper is to use the US NCHRP database (Project NCHRP 17–22) to assess the distribution of impact angle and collision speed in recent ROR accidents. Second, based on the findings of the statistical analysis and on analysis of impact angles and speeds in the literature, an LS-DYNA finite element analysis was carried out to evaluate the normal containment level of concrete barriers in non-standard collisions. The FE model was validated against a crash test of a portable concrete barrier carried out at the UK Transport Research Laboratory (TRL).The accident data analysis for run-off road accidents indicates that a substantial proportion of accidents have an impact angle in excess of 20°. The baseline LS-DYNA model showed good comparison with experimental acceleration severity index (ASI) data and the parametric analysis indicates a very significant influence of impact angle on ASI. Accordingly, a review of European run-off road accidents and the configuration of EN 1317 should be performed.

Application and Improvement of the TRRL (Transport and Road Research Laboratory) High-Speed Laser Profilometer Algorithm with Sensor Fusion

Road roughness detection on highway networks is considered to be vital in order to ensure driving comfort and safety. High-speed profilometers are developed in order to be able to monitor road roughness on highways without affecting the normal traffic flow. This paper focuses on the improvement and the implementation of TRRL-type high-speed laser profilometers. The original design includes 4 laser sensors which are placed along a trailer of 5m length to be towed by a vehicle. As the trailer moves forward, the leading laser sensor measures the road elevation and it is referenced by the other sensors so that the system does not require an inertial sensor for referencing. In the presented work, the original TRRL design is made more compact in order to allow faster operating speeds. The error analysis seen in the original work is extended with the changed geometric design. It is observed that the factor that affects the measurement accuracy the most is surface texture due to its randomness. Therefore the paper proposes a new method which minimizes the texture-caused errors by modelling them with quadratic functions. The performance of the presented profilometer is evaluated by conducting experiments on a road with a known true profile. The accuracy and the repeatability of the system show that the presented profilometer can be used for measuring true profiles with some further improvement.

Teaching traffic safety in Qatari schools: Expectation and reality

Introduction In pursuit of the realization of the Qatar National Vision 2030 (QNV 2030) and to ensure the success of the hosting of the 2022 FIFA World Cup, the Qatari higher authorities have assigned paramount importance to instilling and prorogating traffic awareness among the various community groups and school students. Thus, the establishment of the National Committee for Traffic Safety (NCTS) headed by His Excellency the Prime Minister and Minister of Interior in which the relevant authorities in Qatar have been accomplished. The National Committee for Traffic Safety has prepared a general educational framework for traffic safety program, familiarizing students of all age groups with many of the traffic safety concepts to ensure instilling the needed traffic awareness. This study aims at identifying the effectiveness of the application of the general educational framework of the traffic safety program on experimental basis in some governmental and private schools in Qatar (2015-2013) in preparation to introducing it to all schools in the coming years (if the outcome of the pilot project is proved positive). Study Approach This study will be made as part of the assessment of the implementation of the procedural action plans for teaching traffic safety in Qatar. The study will include conducting a survey among school principals, teachers, parents and students, and measuring the impact of the acquisition of traffic safety knowledge on the students› behavior by examining the school zones and how far the traffic safety measures are applied. It will also follow-up the extra-curricular activities carried out by students outside the classroom. Study Expectations The results of this study are expected to contribute to the enhancement and improvement of the general framework of the proposed educational content before its application on all Qatari schools. As expected in this study, many government and private entities are to be engaged in the preparation of the teaching aids and awareness films to ensure the effective application of the traffic safety concepts on schools. It is also expected that the development of the framework would include the following aspects: preparation of teaching aids, production of awareness films appropriate for each age group and preparation of illustrative pictures and workshops designed to educate teachers before the application of the educational framework. It also aims to improve school zones to enhance traffic safety around schools in accordance with the international safety standards and measures among other improvements.

Traffic fatality trends in four continents based micro level data for three decades

Traffic fatality data for four continents, namely Asia, Africa, Europe and North America, are analysed and modelled here. The analysis is based on gathered traffic death frequencies and rates for over three decades considering 176 countries within the four continents. The predicted values for the coming decade, based on best regression fits, are also analysed. The data sums to over 28,000 records. Official publications, well-known databases, journal papers, official web-sites and personal correspondance were manily employed in collecting the necessary data. While fatlity and vehicular data for the developed countries and few other less developed countries take no time to compile; those for most of the other countries are highly time consuming and distracting, due to the presence of conflicting data, to be processed. It took over three years to gather such data. Such large gathered data for such long period of time are yet not observed in the literature using the common means. Moreover, while future trends of traffic fatalities in Europe and North America are very common and widely presented; that in Asia and Africa are very scarce and lack accuracy due to lack of long-term data. The results indicate that traffic fatalities in Asia and Africa raised from 153 thousands and 46 thousands during 1980 to 384 thousands and 90 thousands deaths during 2011, in respective order; that in Europe and North America dropped from 97 thousands and 57 thousands deaths to 39 thousands and 33 thousands, respectively. It is also intresting to mention that the traffic fatalities in the Arab world sharply increased from 22,145 during 1980 to 37,736 during 2011. It is expected to pass 45 thousands deaths during 2021. The traffic fatalities in the four continents will add up to just 790 thousands considering a flat rate of adjustment factor for underreporting. This however raises serious question regarding underreporting of the official records. Nevertheless, while the roadway deaths in Europe and North America is expected to drop by around 40 and 20%, respectively by the year 2025, according to the models developed here, that in Asia and Africa is expected to increase by around 15 and 70%, respectively. The fatality rates per population followed a very similar pattern, but steeper, of the fatality frequency. There are many contributory factors leading to such high traffic deaths in Asia and Africa. These include, among many other factors, lack of measurable long term safety plans on real ground, inconsistent handling of traffic safety strategies, poor involvement of NGO’s, poor coordination between various stake holders, poor research involvement in the traffic safety crises and limited post-accident rehabilitation centres. Selected

Are we ready to hand over the steering wheel? [Self-driving cars

The main cause of traffic accidents is human error, but sorting out the tech challenges of driverless cars solves only half the problem. There are a multitude of reasons automated technology could benefit us. An estimated 90 per cent of accidents are caused by driver error.The idea of a self-driving vehicle isn't new. In the 1960s researchers at the Transport and Road Research Laboratory in Berkshire developed a'self-driving' Citroen DS car that was able to follow a series of magnetic cables embedded in the road. Since then, the industry has followed an evolutionary approach, gradually adding elements of automated technology to vehicles, like parking and lane sensors. Some of the technology, like telematics, has been around for over a decade. Telematics itself is a catch-all term for the converging of telecommunications technology with informatics. In recent times, this has led to a whole host of new developments, including parking sensors, GPS navigation, and automatic driver-assistance technology.

To investigate the fundamental causes of utility air voids content failures in asphalt layers to achieve Specification for the Reinstatement of Openings in Highways (SROH) compliant performance

The linkage between air voids content and durability in footways reinstatements with the limits currently in SROH is non-proven and unsupported by evidential research or trial data. Compounding of errors, particularly in density measurement of core samples and subsequent variability, generate biased air void content results that make the compliance largely a matter of chance. This led to a very wide range of predicted outcomes, putting both the contractor and the client at unacceptable risk. The use of a measured in situ air voids content criteria in a specification for footway reinstatements, where the entire operation is in restricted areas with hand laying process using recipe mixed materials, cannot be sustained on technical grounds with respect to relevant British Standard and Transport Research Laboratory (TRL) guide. Taking account of the service loads, nature and scale of works in footways, an in-service guarantee by the undertaker for an agreed extended period, linked to an allowable intervention level, could be a simple, realistic and acceptable solution, ensuring a durable reinstatement that removes the financial risk of failure from the highway authority.

Reliability design optimization of vehicle front-end structure for pedestrian lower extremity protection under multiple impact cases

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 Pedestrian Legform Impactor (TRL-PLI) test has been conducted according to the specifications in European Union (EU) regulation. At the same time, a Flexible Pedestrian Legform Impactor (Flex-PLI), which has flexible femur and tibia, is examined in European New Car Assessment Program (Euro-NCAP) rating system. To minimize injury risks of pedestrian lower extremity, this paper presents the design optimization of a typical vehicle front-end structure subjected to two different impact cases of TRL-PLI and Flex-PLI. Several approaches involving sampling techniques, surrogate model, multiobjective optimization algorithm and reliability analysis are introduced and applied. Four different basis functions of radial basis function (RBF) surrogate model are adopted for achieving more accurate solutions for structural optimization and reliability analysis. It shows that the accuracy of the basis function is different and the best one is selected for approximate the objective and constraint functions. In order to take into account the effect of design variables uncertainty, the reliability-based design optimization (RBDO) is conducted, and a Monte Carlo Simulation (MCS) is adopted to generate random distributions of the constraint functions for each design. The differences of the different Pareto fronts of the deterministic optimization and RBDO are compared and analyzed in this study. Finally, the reliability-based optimum design result is verified by using test validation. It is shown that the pedestrian lower extremity injury can be substantially improved for meeting product development requirements through the proposed approach.

Engineering Properties and Shrinkage Limit of Swelling Soils in Greece

The engineering problems of swelling soil have arisen in Greece as well as in other parts of the world when a combination of unsaturated clay soils and uneven distribution of rainfall can occur. Expansive soil cause significant damage to structure and roadways by cyclic shrink-swell within the active zone of soil. This is one laboratory way to identify the shrinkage potential of clay soil in Greece. Laboratory tests were performed to examine the effectiveness of various methods in alleviating the adverse results of seasonal swelling – shrinking in connection with roads and buildings foundation, giving special attention to shrinkage limit test using the mercury apparatus, suggested by the Transport and Road Research Laboratory.