New Frontiers in Road and Airport Engineering

To analyze RAP, mixing mode and additives impacted on fatigue characteristics of recycled SMA asphalt mixtures, the hot and warm recycled SMA mixtures with 0%, 20%, and 30% RAP are designed. The warm recycled mixtures are prepared with adding 3% Sasobit into the hot recycled SMA mixture using dry-processing and wet-processing methods. Four-point bending fatigue test is conducted on the recycled mixtures, and the dissipated energy theory is employed to analyze fatigue characteristics of the recycled mixtures. It shows that: (1) the relationship between fatigue life and cumulative dissipated energy of the recycled mixtures does not change with the variation of RAP content and mixing mode. There is a good linear relationship between fatigue life and cumulative dissipated energy of the recycled mixtures, which can be represented by a unique relation equation. (2) When RAP content is lower than 20%, fatigue characteristics of the recycled mixtures has a little change, while when RAP content is higher than 20%, fatigue characteristics of the recycled mixtures experiences a sharp decline. (3) Sasobit additive has an adverse impact on fatigue characteristics of the mixtures without RAP.

Crumb rubber modifier (CRM), made from scrap tires, has been introduced into the production of different types of hot mix asphalt (HMA) in either wet or dry process. There has been few research about the interaction between asphalt and the crumb rubbers added in the dry process. In the study, dynamic shear rheometer (DSR) and atomic force microscopy (AFM) were used to explore the interaction between the asphalt binder and CRM in dry and wet process. The results indicated: (1) rubberized binder in dry process have similar modulus, phase angle and complex viscosity with wet process, regardless of unaging or short-term aging, (2) rubberized asphalt in dry process has lower roughness of topographical image than wet process before short-term aging. However, the short-term aging may decrease the difference of the microstructures of the binders in two processes, i.e., wet and dry processes.

Aging of asphalt binders causes the changes in the microstructure of the asphalt binders, consequently, in the mechanical properties. In this study, aging of short-term and long-term was tested on both base and modified asphalt binders using rotating thin film oven (RTFO) and pressure ageing vessel (PAV), respectively. The changes in the nano-mechanical properties were measured using atomic force microscope (AFM) technology. The results indicated: (1) the nano-adhesive forces from AFM were increased for both base and modified asphalt binders after RTFO aging; and (2) the nano-adhesive force was reduced for both base and modified binder, but the former was reduced higher than the later after PAV aging.

The objective of this study is to investigate the effects of tack coat material type, application rate, surface type, and surface characteristics on the interface bond strength. In this study, the portable bond strength tester (PBST) was adopted to measure the bond strength. A suitable sample preparation procedure was then defined. Test Results demonstrated that increasing the application rate increased interface bond strength up to a maximum, then decreased gradually. Optimum application rate varied from 0.6~0.8 L/m², depending on the tack coat and the interface types. The tack coat type was shown to play a key role in the interface bonding. Consistency was observed in the ranking of the bonding strength of all asphalt types on different surfaces, which is sequenced as follows: epoxy asphalt>hot asphalt>asphalt emulsion>cutback. Among the aforementioned asphalt, the bonding performance of epoxy asphalt and asphalt emulsions are most sensitive to the presence of dust.

This study aims to investigate the effect of fiber mixed into asphalt mastic on the high and low temperature properties in a microscopic scale. In order to get the performances of fiber asphalt mastic, a serial of loboratory tests were conducted including the repeated creep recovery test (RCRT), the multi-stress creep recovery test (MCRT), and the bending creep stiffness test (BCST), also, the influence factors such as fiber contents, temperature, stress level, and fiber types were evaluated, respectively. The results indicate that: (1) fiber can improve the properties of asphalt mastic at high and low temperature, and this reinforcement effect is increased with increasing of fiber contents in a certain range. Moreover, it is sensitive to temperature, i.e., the increase of temperature can make the accumulated strain and its rate of fiber asphalt mastic all increase; (2) the effect of the stress level on high temperature performence is significant, where the mastic recovery rate R is decreased and irreversible creep compliance J_nr is increased with increasing of the stress value; and (3) the influence of fiber types on R value enhancement and J_nr reduction for mastic is remarkable under the high stress level, and its result is ranked in a decreased order as follows: basalt fiber, polyester fiber, glass fiber, and pure asphalt mastic [control].

Different characteristics of aggregates has significant impact on the high modulus mixture properties of hard asphalt (such as high temperature properties, modulus, and fatigue resistance). This paper chooses two kinds of aggregates (basalt and limestone) with obvious differences. Based on the Aggregate Image Measurement System (AIMS), this paper made detailed comparison and analysis on all characteristics of the two kinds of aggregates. Referring to the French high modulus mix design process, the various performance indicators coordinated design methods were tested on the high modulus mixture of hard asphalt. Results show that, it can be achieved a balanced design of high temperature performance, modulus, and fatigue resistance properties on the mixture thronging the gradation and the hard asphalt dosage adjustment, for different properties aggregate.

The healing property has a great influence on the strength and lifespan of asphalt pavement. This study point out the dichotomy between self-healing property and strength in polymer modified asphalt. Afterwards, high-efficient self-healing asphalt was designed by incorporating ethylene methyl acrylate (EMAA) copolymer into base asphalt. T-peel healing test was employed to analyze the relationship between self-healing strength and various rest times and several temperatures. At last, the self-healing abilities of base asphalt and ionomer modified asphalt were evaluated. The results demonstrated that the relationship between the asphalt healing strength and the rest times follows power function. Meanwhile, EMAAs hold the potential to enhance self-healing ability of base asphalt. It is speculated that ionic bond is responsible for the improvement of healing ability of ionomer modified asphalt. This study provides a new insight into the research of the healing mechanism and evaluation methodology.

The objective of the paper is to investigate the influence of bitumen nature on complex modulus and fatigue resistance of bituminous mixtures produced with reclaimed asphalt pavement (RAP). Eight distinct mixtures were produced with eight different modified and unmodified base binders. RAP content was fixed equal to 20% for all mixtures. For each mixture, the corresponding binder blend was produced by mixing the base binder with RAP-extracted binder, in the same proportions. A total of 16 binders (eight base binders and eight binder blends) were therefore used in the study. Both advanced and classical tests commonly used by road paving industry in Europe were performed. Complex modulus (at 15°C and 10 Hz) and fatigue (at 10°C and 25 Hz) DSR tests were carried out on all binders. Two-point bending complex modulus (at 15°C and 10 Hz) and fatigue (at 10°C and 25 Hz) tests were carried out on trapezoidal samples of mixtures. Complex modulus and fatigue resistance of mixtures appeared to vary significantly depending on the nature of the base binder. However, clear correspondences between values obtained for mixtures and corresponding binders could not be found.

Ground tire rubber (GTR) has been used for several decades to improve the performance characteristics of asphalt pavement in the USA. It is well known that the engineering properties of asphalt pavement containing GTR are dependent on the rubber size, type, concentration, and etc. Many researchers found that the utilization of a proper GTR in asphalt pavement can help the reduction of the cost and extend the pavement service life with some other benefits, such as environmental protection, solid waste reduction, and so on. However, the challenges to produce the GTR asphalt pavements are to need a field blended system to yield the rubberized asphalt binder to mix with aggregate because the rubberized asphalt binder generally has a serious segregation problem during the storage procedure. This system is costly and the quality of the modified binder is generally dependent on various factors, and thus it is not easy to control. Nowadays, a promising technology is to produce GTR binder in the asphalt plant and terminally blended GTR binders are shipped to asphalt mixing plant as the conventional SBS binders without any additional treatments. This technology is broadly being used in different regions of USA recently. However, it is necessary to explore the performance properties of terminally blended GTRs compared to the traditional laboratory blended GTRs. In this study, one base binder (PG 64-16) was used to produce terminally blended GTRs and laboratory blended GTRs, originally from Nevada, USA. The test results showed that the rheological properties (viscosity, failure temperature, phase angle, etc.) of terminally blended GTRs are comparable with these laboratory blended GTRs. Therefore, it is recommended to use terminally blended GTRs in the real world.

The microstructure of bitumen is responsible for the rheological properties and pavement performance, the change of microstructure had a significant impact on the bitumen behavior. Atomic Force Microscopy (AFM) technology has a great advantage on microstructure analysis and the microstructure had been proven to be a unique and reproducible property of a bitumen, but the challenge in applying AFM technology is to obtain samples which can reflect the true microstructure of bitumen. The paper mainly investigated the sample preparation, probe selection, and the structural characterization of the bitumen at the nanoscale by AFM. The results showed that molding method can guarantee the reproducibility and stability of sample and the AFM images obtained could reflect true microstructure of bitumen. According to basic modulus principle, nominal spring constant of AFM probe should be lower than 5 N/m at room temperature in tapping-mode. In addition, AFM cantilever material with back coating was recommended as results of the opacity of bitumen. “Bee-shaped” structure with several micrometers in length and 47–55 nanometers in height randomly distributing presented in base bitumen and SBS modified bitumen, the results were in agreement with previous studies. Although many studies reported the component of bee-shaped structure, it still remained unclear at present.

The fatigue performance of base asphalt mixture (AC-13), asphalt rubber mixture (ARAC-13), and SBS modified asphalt mixture (SBS-AC13) were characterized using four-point blending fatigue test. The fatigue performance comparison considering self-healing or not were performed between AC-13, ARAC-13, and SBS-AC13, which were prepared at certain designed air void for each kind of mixture. Besides, comparison between AC-13, ARAC-13, and SBS-AC13 with the same asphalt content was also conducted. Furthermore, wheel tracking test was conducted to characterize high temperature performance as supplementary. Fatigue life of ARAC-13 is much better than SBS-AC13 and AC-13 at designed air void whether or not self-healing is considered meanwhile self-healing capacity coincides with the fatigue life ranking. For mixtures with the same asphalt content, SBS-AC13 offers better fatigue performance over ARAC-13 whether or not self-healing is considered while ARAC-13 offers advantage over SBS-AC13 with respect to self-healing capacity. The fitted fatigue equations show that the fatigue life is sensitivity to strain, asphalt content, and air void whether self-healing is considered or not. The high temperature performance of ARAC-13 is a little better than that of SBS-AC13. In general, ARAC-13 is recommended considering its excellent fatigue performance and self-healing capacity, meanwhile its high temperature performance satisfies demand.

Crumb rubber modified asphalts (CRMA) mastic is an important part of CRMA mixture, however, the testing condition restricts its research in our country. In order to study the effect of fillers on the high temperature properties of CRMA mastic, mineral powder, and cement were selected as the fillers and the CRMA mastic were prepared using different filler-to-binder ratios (F/B). The study evaluated the high temperature properties of different CRMA mastic by zero shear viscosity and fail temperature. Test results indicate that with the increase of F/B, fail temperature and zero shear viscosity in the creep recovery phase of CRMA mastic are gradually larger, and the high temperature properties of CRMA mastic has been significantly improved. Compared with the same F/B, the fail temperature and zero shear viscosity in the creep recovery phase of CRMA mastic, which using mineral powder as filler is larger than the one, which using cement as filler. Mineral powder is better than cement in the aspect of improving the high temperature properties of CRMA mastic. The result of this paper can provide a theoretical basis for improving the road performance of CRMA mastic.

The failures of bonding between pavement layers are believed to be associated with shoving and may cause other distresses. The objective of this study is to investigate the influence factors on shear strength, including types of tack coat, application rate, upper layer type, test temperature, as well as interface contamination. A test device which is capable of applying normal stress is employed to evaluate the shear properties between layers. Results showed that Novechip® performed the best among all the upper layers. Self-developed polymer modified emulsified asphalt performed best among all the tack coats. The interface contamination between layers significantly decreased the shear strength. Test temperature is proven to be the most significant factors that affect the shear strength. The results presented in this study may potentially provide meaningful information on the selection and installation of tack coat between pavement layers.

When the hot-mix asphalt (HMA) mixture is placed in the field, it is already aged by the short-term aging (STA) during hauling and queuing. Then, the mixture starts aging during the service for a long period of time, which is called the long-term aging (LTA). It is generally agreed that the longer the service life, the higher the aging level. However, from the examination of aging level of expressway asphalt pavements in Korea, a significant difference in LTA level was detected between two types of asphalt mixes [stone mastic asphalt (SMA) and dense-graded asphalt (DGA)]. To examine this finding more elaborately, the works were extended to the artificial aging of SMA and DGA mixtures. The STA was performed for 1 hour at 160°C on the loose mixture, which was blended with a paddle mixer, and then the LTA was performed for 48 and 72 hours at 110°C on the specimens made of STA-treated mixes. The aging level was evaluated by the gel-permeation chromatography (GPC) test in terms of large molecular size (LMS) directly from the mixture particles. The study results found out that there were significant differences in aging levels between two mixture types (SMA and DGA).

In general, the binder properties of asphalt mixture can be measured only when the binder is recovered from the mixture. However, this study showed the method of estimating the binder property reliably using gel-permeation chromatograph (GPC) technique without binder recovery from loose mixes, compacted specimens or field cores. The large molecular size (LMS) of asphalt can be measured by the GPC test directly from the asphalt mixture sample and then used to estimate necessary property of the binder. To show its applicability, this study estimated the service life plus four properties [the stiffness (G*/sinδ), absolute viscosity (AVS), penetration (PEN), and DSR pass/fail (P/F) temperature] based on the LMS. Many cores taken from 6 sites in Korean Expressways and a lab-prepared mixture were used. The regression analyses found that the AVS and P/F temperature showed very high correlations (R² > 0.98) with LMS. The G*/sinδ, PEN, and service life had high correlations with LMS showing R²≒0.93, 0.92, and 0.88, respectively. Therefore, LMS is a good prediction tool for binder’s physical properties. Therefore, it is possible to say that the LMS will be a reliable prediction medium of physical properties of asphalt binder in the mix.

In this paper, the influence of RAP state on warm recycled mixture gradation design was experimentally studied. Different kinds of mixture gradations with different content and state of RAP were synthesized. The concept of “variation degree of gradation” was proposed to quantify the uncertainty of the recycled mixture gradation. It was described as the different passing rate at each sieve size between the two kinds of gradations that respectively synthesized by using the RAP screening result of pre-extracting and post-extracting. Their properties were then tested and compared with each other. The results show that, when the variation degree of gradation is bigger, the state of RAP should be simplified to complete mixing state, that is to say, the recycling mixture gradation should be synthesized by using the RAP post-extracting screening result; but when it is smaller, the state of RAP could also be simplified to black aggregate state, i.e., using the RAP pre-extracting screening result to synthesize gradation is also feasible.

Although permeable pavements are becoming increasingly common for stormwater management across the world, they are mostly used in parking lots, basic access streets, recreation areas, and landscaped areas, all of which carry very light, slow moving traffic. Very little research has been undertaken on the behavior of permeable interlocking concrete pavement as a surface and structure to support more heavy trucks. To understand how permeable interlocking concrete pavements (PICP) perform under heavy traffic loading, a research project was conducted at the University of California Pavement Research Center (UCPRC) with funding from the interlocking concrete pavement industry. The results of this project were used to develop a mechanistic-empirical (M-E) design method for PICP. This method is based on mechanistic analysis and was partially validated with accelerated pavement testing (APT) results. This paper presents a summary of the structural performance of PICP under heavy traffic loading with a Heavy Vehicle Simulator (HVS). The results include the rutting performance of PICP sections with three different thicknesses of subbase layer (reservoir layer) under dry, wet, and drained conditions and with different load levels. The rut development with loading repetitions in the surface, base, and subgrade layers is discussed.

The typical structures of frequently used semi rigid base, asphalt treated macadam laying on semi-rigid base and graded broken stone laying on semi-rigid base in Guangzhou-Heyuan Expressway were analyzed on structural stress. Comparative analyses on the load response characters with asphalt pavement structure layers with different base were carried out. Combined effects of gradation, modulus, and thickness of Asphalt treated macadam layer with field investigation of composite base, design schemes of asphalt pavement with rigid-flexible composite base were proposed for expressway in Guangdong.

Permanent deformation of loess subgrade is calculated under the condition of light and heavy vehicle running in respective lanes, which is the common traffic organization of high-grade highways. Based on repeated load triaxial test results, ABAQUS software and elastic mechanics method were used to analyze the stress of asphalt pavement structure under the coupling effect of subgrade permanent deformation and vehicle load in this paper. The results indicated that the maximum tensile stress on bottom of semi-rigid base was much bigger when considering the effect of subgrade permanent deformation. Permanent deformation of loess subgrade on condition of vehicle running in the lanes freely and tensile stress on bottom of semi-rigid base under the effect of permanent deformation were both calculated, which proved that the maximum tensile stress on bottom of semi-rigid base increased signally. The semi-rigid base cracked gradually under the coupling effect of subgrade permanent deformation and vehicle load, which could lead to the lower service level and reduced fatigue life of semi-rigid base asphalt pavement.

With the current large-scale construction of paved roads, continuous development of science and technology, and higher service requirements. Smart road is becoming the research hotspot in the world. But the most present research concentrate on some single intelligent functions of road or some specific technology such as snow-melting, solar energy harvesting, etc. There is no explicit definition or integrated framework for smart road. In this paper, on the basis of related concepts and researches of smart road at home and aboard, combined with some demonstration programs and technology trials, first, put forward a explicit definition and functions of smart road, then subdivided the functions, analyzed the key technologies and core problems of implementing each sub-function, finally summarized the definition, functions, and technologies, built an integrated framework of smart road, include physical frame and logical frame. The definition and framework construction would define the direction of smart road research and development to some extent.

The correlations between tire-pavement noises and pavement surface characteristics have been investigated for many decades, but temperature effects on these correlations are not clear yet. The objective of this paper was to investigate temperature effects on correlations between noise levels and surface characteristics correlations. Tire-pavement noises were measured quarterly by on-board sound intensity (OBSI) method on four types of asphalt pavements on the 2009 National Center for Asphalt Technology (NCAT) test track. Air and pavement temperatures were also recorded during those noise measurements. Four pavement surface characteristics (texture, porosity, roughness, and stiffness) were correlated with noise levels using a linear regression method. Temperature effects were established by comparing correlation coefficients between noise levels and surface characteristics with/without temperature correction. The results showed that, air temperature influenced the correlations between noise levels and surface textures, and temperature corrections were necessary to be taken before analysis. It would be benefit to data processing during tire-pavement noise research.

This paper presents a microstructural level finite element (FE) model of asphalt mixture for four point bending beam fatigue analysis. Digital image processing techniques were applied to convert a conventional image into numerical model of asphalt mixture, which contains the actual material heterogeneity and microstructure. The digital model was modified and designed with different volumetric properties. Subsequently, FE analysis on fatigue damage was conducted with the consideration of 5 levels of air-void and asphalt contents. It was found that the volumetric properties have significant effects on fatigue behaviour of asphalt mixture, the change in asphalt content is more sensitive than air void content change if a controlled strain fatigue loading mode is performed, which proved the traditional research results under laboratory fatigue tests. However, the FE analysis also indicate the difference in results under different loading direction and loading mode when material heterogeneity was take into account. The analysis indicate that the proposed method and model can be extended to other performance analysis such as rutting and low temperature cracking due to its convenience to redesign and to retest with different loading conditions and material properties.

In this paper, the finite element method was used to analyze the influence of principal stress distribution on asphalt pavement. Three-dimensional finite element model under double-round uniform load was established for multi-layer asphalt pavement with flexible base and stress components of each node were analyzed based on Drucker-Prager (D-P) criterion. A new index, asphalt pavement potential damage index (APPDI), was proposed. Two conclusions were obtained as follow: firstly, the principal stress composition has a great influence on asphalt pavement damage. Secondly, the comparative analysis of the maximum APPDI and stress in each layer indicated that APPDI could be used as the damage evaluation index of pavement structures.

Considering the large amount of highway asset items, a statistically valid data sampling method is required for the level of service inspection of highways. The presented paper discussed the determination of sample size for the pass/fail highway inspection approach. The historical highway inspection data from Tennessee were collected for demonstration. It was found that passing percent is the most significant factor for sample size while population size has little influence. An effective approach to improve the precision at lower management levels without increasing sample size is to use an average sample size for all different subgroups. To investigate the necessity of stratified sampling, statistical paired t-tests were conducted to identify if the passing percent of subgroups are significantly different with the whole state. The results showed no significant difference between interstates and state routes. Although sampling at district levels could potentially improve the significance level of half of the districts, the sample size would be multiplied and is not cost-effective.

We present a methodology for the joint optimization of flexible pavement maintenance, rehabilitation, and reconstruction (MR&R) activities. The majority of existing pavement management systems (PMS) do not optimize reconstruction jointly with maintenance and rehabilitation policies. We show that not accounting for reconstruction in maintenance and rehabilitation planning results in suboptimal policies for pavements undergoing cumulative damages in the underlying layers (base, sub-base, or subgrade). We use a history-dependent pavement deterioration model to account for the influence of MR&R history on the deterioration rate. We present dynamic programming solutions using an augmented state, which includes current surface condition and age. The optimal maintenance and resurfacing policies and the optimal time between reconstructions are obtained and graphically represented for a range of real-world pavements.

Long-life flexible pavements with more than 40 years of life expectancy are often found to be the most economical solution for heavily trafficked roads. Based on long-life flexible pavement design, construction, and maintenance practices in Hong Kong, this paper discusses four issues related to long-life flexible pavements: the cost and benefit, distresses, binder aging, and maintenance strategies. The studies found that long-life pavements are the most economical and environmentally friendly option for moderately and heavily trafficked roads. Long-life pavement cannot be realized by simply increasing asphalt concrete thickness; instead, attentions also need to be paid to construction details. A major distress mode is interfacial deterioration caused by inadequate bonding and high air voids content at the interface. In contrary to long-held belief that asphalt binder in deep pavement layer does not age, recent studies found binder throughout the long-life pavement structure is severely aged after long-time field service. Current practices and field experiments indicate that certain maintenance measures such as crack sealing are not necessary for long-life pavements in certain climate regions. Therefore, long-life pavement demands less maintenance treatments. The findings are expected to contribute to better practices in long-life flexible pavement design, construction, and maintenance.

Oversize-overweight (OSOW) permit vehicles often operate using heavier axle loads than typical truck traffic, in addition to their higher gross vehicle weights. Heavy vehicles are a special concern to pavement engineers due to their correspondingly higher likelihood of causing pavement deterioration. Using a six-year database of single-trip overweight (OW) permits issued in Wisconsin and the results of an extensive route mapping effort, axle load spectra (ALS) were calculated for OW permit vehicles for selected state highway segments. Baseline traffic parameters from the Wisconsin Department of Transportation (WisDOT) corresponding to the selected segments were disaggregated, and the OW ALS were meshed with baseline traffic to create combined ALS. The comparative results of Mechanistic-Empirical Pavement Design Guide (MEPDG) analyses on segments of interest using baseline ALS versus meshed ALS allowed for the estimation of differential pavement damage resulting from the OW permit vehicles. For example, the average per-vehicle deterioration rate from OW trucks on State Trunk Highway 11 ranged from 1.09 to 6.69 times the baseline rate for different types of pavement deterioration. This methodology can be applied to any roadway in order to estimate the pavement effects caused by the addition of vehicles to baseline traffic.

To investigate how the driving behavior of emergency braking in the haze weather condition differs from that in clear weather condition and how the driving simulator fidelity influences the behavioral differences, this paper employs a high fidelity driving simulator with 8-degree of freedom (DoF). A static simulator with the 8-DoF motion system turned off is used as well to study the driving behavior of emergency braking for a comparison to the high fidelity one. Four scenarios with a combination of clear or haze weather conditions and static (0-DoF) or dynamic simulator (8-DoF) are set up for the investigation. The two weather conditions are defined by the visibility. The results show that the visibility of weather conditions does have significant impacts on the emergency deceleration behavior and reaction time and the haze weather condition results in shorter reaction time. The fidelity of the driving simulator does have impacts on the driving behavior of emergency braking as well.

Collisions at intersections are considered a main contributor to the relatively high accident rates in China. One of the reasons is that drivers cannot get the full information needed to make an objective judgment about road conditions ahead. If collision detection is made and issued before drivers notice the danger, it would be of great importance for improving the traffic safety. In this paper, we proposed a collision detection algorithm to determine the possibility of collisions at T-shaped intersections based on location based service (LBS), which integrates global positioning system (GPS), inertial measurement unit (IMU), and other vehicle sensors to provide real-time state information of the vehicles approaching to the intersection. Results showed that the successful warning rate is as high as 81.7%, which indicates that the detection method is effective for alerting drivers to dangers beforehand.

The presented study aimed to determine how much the recent trend in motorcycle safety was influenced by weather on the example of Indiana. To confirm this hypothesis, a statistical crash counts model was developed to connect the weather with the monthly and annual number of motorcycle crashes and to estimate the hypothetical trend under the assumption of a seasonal weather pattern perfectly repetitive in annual cycles. The study results indicate that the weather does increase the motorcycle crashes under low atmospheric precipitation and warm temperatures, most likely due to the increased presence of motorcycles on the roads. This effect has obscured the Indiana trend in the last several years. It is useful to analyze the trends in crash statistics adjusted for the weather effect, particularly, if the weather continues to fluctuate considerably and randomly.

Existing anti-crash facilities, such as anti-collision sand barrels before crash barriers triangle end, did not meet the safety protection requirements and national standards. So, considerable modification of the existing facilities was needed to improve protection effect. According to the safety performance evaluation of highway guardrail standards, impact simulations of car with 100km/h were carried out by finite element analysis. Simulations of frontal, oblique or side impact between car and modified crash cushion were analyzed. With the help of modified crash cushion, vehicles were slowly stopped and maintained in normal sate. Crash cushion energy absorption components completely deformed, and in the greatest protection function. Then, frontal impact test with real vehicle was carried out, the result indicated that the simulations could reflect the characteristics of improved crash cushion, and vehicle safety could be improved by the modified crash cushion.

The multimodal transportation network includes a mix of inherently different modes. In addition to differences in price, range, and comfort of travel, these modes differ in mass and velocity, which correspond to different orders of magnitude in the kinetic energy carried. This discrepancy in kinetic energy affects both the level of protection of each mode, and the level of damage it can inflict on users of other modes. Unfortunately, accounting for both sides of a crash is often overlooked. While the quantities and variables of collected data continue to increase, the analyses conducted and the tools developed remain focused on the victims of crashes. The existing approach limits the ability to explore the underlying mechanism of traffic crashes since there are two sides to every crash. This manuscript proposes a framework for studying traffic safety that takes into account the interaction between all modes in a network. At the core of the framework is a square matrix, I. The rows and columns represent different modes such that element Iij is the number of injuries that were suffered by mode i, which were inflicted by mode j. The distinction between suffered and inflicted injuries is not related to the fault of the involved parties. The distinction lies in which of the two parties experienced the injury. For example, if two vehicles are involved in a crash that resulted in a single injury, the vehicle that experienced the injury is identified as the one that suffered the injury while the other vehicle is the one that inflicted the injury. If an injury is experienced in both vehicles then both vehicles suffered one injury and inflicted one injury. A relative vulnerability index can be calculated for specific mode-pairs, for individual modes, and for an entire geographical region. An empirical application using data from California reveals, amongst other things, that the relative vulnerability of pedestrian and bicyclist are orders of magnitude higher than motorized modes. Applying this methodology to different locations around the globe would provide insights the relative vulnerability of different modes under different mode-splits, different road designs, and different road user cultures.

Recently, with the development of urban road net and the shortage of land resources, underground expressway has a rapid development, but the associated research of traffic safety is lagging. The traffic flow data and method of mathematical statistics is used to analyze the difference of vehicles running index such as speed, space headway and lateral movement in underground expressway comparing to such things in expressway above the ground. It also indicates the possible impact on the safe operation of the underground expressway caused by these differences, and gives some suggestions on the improvement of the underground highway safety from the point of safety of vehicle operation.