The Development of Crash Modification Factors program studied the safety performance of various stop-controlled intersections for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated the safety effectiveness of multiple low-cost treatments at stop-controlled intersections. Improvements included basic signing and pavement markings. This strategy is intended to reduce the frequency and severity of crashes at stop-controlled intersections by alerting drivers to the presence and type of approaching intersection. Geometric, traffic, and crash data were obtained at three- and four-legged, two- and four-lane major road, and urban and rural stop-controlled intersections in South Carolina. To account for potential selection bias and regression to the mean, an empirical Bayesian before–after analysis was conducted, using reference groups of untreated intersections with similar characteristics to the treated sites. The analysis also controlled for changes in traffic volumes throughout time and time trends in crash counts unrelated to the treatments. The aggregate results indicate reductions for all crash types analyzed (i.e., total, fatal and injury, rear-end, right-angle, and nighttime). The reductions are statistically significant at the 95-percent confidence level for all crash types. For all crash types combined, the crash modification factors (CMFs) are 0.917 for all severities and 0.899 for fatal and injury crashes. The CMFs for rear-end, right-angle, and nighttime crashes are 0.933, 0.941, and 0.853, respectively. The benefit–cost ratio estimated with conservative cost and service life assumptions is 12.4 to 1 for total crashes at unsignalized intersections. The results suggest that the multiple low-cost treatments, even with conservative assumptions on cost, service life, and the value of a statistical life, can be cost effective
Vision Zero is a priority road safety framework for Canada, as outlined by the Canadian Council of Motor Transport Administrators (CCMTA) in the release of their Road Safety Strategy 2025 (RSS 2025). The strategy, released in 2016, focuses on the long term of ensuring Canada’s roads are the safest in the world, while adding a greater focus on the vision of “towards zero” serious injuries and fatalities on the roadways. The Vision Zero Advocate Institute, supported by ATS Traffic, is the market leader in Vision Zero. Current studies point to a clear disparity in municipal comprehension and implementation of Vision Zero initiatives. The Vision Zero Advocate Institute closes that gap. (from the introduction)
Tack coats are thin applications of asphalt emulsion between the layers of a pavement structure with the role of enhancing adhesion. Fog seals are thin emulsion applications to pavement surface for protecting the surface from oxidation and water ingress, as well as reducing the risk of raveling and stone loss. One of the downsides of using asphalt emulsions for these applications is the required breaking and curing time. Even after curing, traditional emulsion grades will track onto nearby surfaces. Slow curing fog seals require longer road closures and/or a light sand application before trafficking. This paper presents the development stages of a non-tracking emulsion developed for bond coats and fog seals. The emulsion was formulated and engineered to be fast curing and provide a hard, non-tracking surface, suitable to support traffic without the use of sand application. Its tracking properties were assessed using novel tracking and curing tests, and its performance as a bond coat was measured using the tack coat shear test developed by McAsphalt. Trial projects of tack coating and fog seals were conducted from 2013 to 2016 throughout several Canadian provinces. Performance to date in the field, as well as some observed challenges, are presented.
Fatigue resistance is an important factor for high quality Hot Mix Asphalt (HMA). Asphalt cements containing higher concentrations of polymer are known to be more strain tolerant, which can provide improved fatigue resistance in HMA. Use of polymer modified asphalt cement is a proven way to improve fatigue performance. Many municipalities and the Ontario Ministry of Transportation have implemented the Double Edge Notched Tension (DENT) test to improve the fatigue performance of the asphalt cement and the corresponding HMA. The DENT test is performed at an intermediate temperature that should correspond with fatigue performance. The Multiple Stress Creep Recovery (MSCR) test is an environmental test that measures the compliance and elastic response of an asphalt binder. The MSCR test is conducted at the high-performance grade temperature based on the local 7-day maximum temperature. The results from this research have shown that there is no clear relationship between increasing concentration of polymer modification and DENT performance. On the other hand, the percent recovery showed a very good correlation with polymer modification and performance. Based on the information presented in this paper, the MSCR is ultimately expected to be validated by HMA fatigue testing while the DENT is not.
The Development of Crash Modification Factors program conducted the safety evaluation of red-light indicator lights (RLILs) at intersections for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated safety effectiveness of RLILs. RLILs are auxiliary lights mounted on signal heads, mast arms, or poles that are directly connected to a traffic-control signal. The RLIL activates at the onset of the red phase and allows an enforcement officer to observe red-light running from downstream of the intersection. This strategy is intended to reduce the frequency of crashes resulting from drivers disobeying traffic signals by providing a safer and more efficient means for police to enforce the red interval. Geometric, traffic, and crash data were obtained at treated four-legged signalized intersections in Florida. To account for potential selection bias and regression-to-the-mean, an empirical Bayes before–after analysis was conducted using reference groups of untreated four-legged signalized intersections with characteristics similar to those of the treated sites. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment. Results indicate statistically significant crash reductions for most crash types. Disobeyed signal crashes had an estimated crash modification factor (CMF) of 0.71. Total crashes, fatal and injury crashes, right-angle, and left-turn crashes had estimated CMFs of 0.94, 0.86, 0.91, and 0.60, respectively. The benefit-cost ratio estimated with conservative cost and service life assumptions was 92:1 for four-legged signalized intersections. The results suggest that the treatment, even with conservative assumptions on cost, service life, and the value of a statistical life, can be cost effective. In addition to the crash-related benefits, RLILs can improve the efficiency and safety of red-light running enforcement efforts. While this study did not evaluate the efficiency and safety impacts with respect to enforcement, it should be noted that RLILs do allow police to observe violators from a downstream position, eliminating the need for a second observer (upstream) and the need to pursue a violator through the red light.
The authors of the original 2015 paper entitled “Cold Winter and Early Asphalt Pavement Cracking Observed in Ontario” would like to acknowledge the detailed response provided by Dr. Keith MacInnis, Senior Technical Advisor, Canadian Asphalt Industries, Hamilton, Ontario. We also appreciate that the above noted paper generated interest and discussion around this critical topic. The subject described in the paper was of great importance to the road owners, and the Canadian Technical Asphalt Association (CTAA) is the best forum for this kind of discussion. This paper provides comments from the lead author of the paper in response to the comments that were provided by Dr. Keith MacInnis on the original 2015 paper.
Light Colour Asphalt Pavement (LCAP) is a process of designing and constructing asphalt pavements that meets the Leadership in Energy and Environmental Design (LEED) Solar Reflective Index (SRI) requirement that at a minimum 50 percent of the hardscape can be constructed using materials having an SRI value of 29 or higher. The purpose of the development of LCAP is to provide developers looking to achieve LEED certification with a paving alternative that provides performance that is equivalent to conventional asphalt pavement, but that will also meet the requirement of LEED. The LCAP process includes aggregate selection, asphalt mix modification, placement of asphalt mic, stripping of surface asphalt film from new pavement, and evaluation of reflectivity of aggregates, mixes, and in-place pavements. The very light colour aggregate from Coco’s Badgley Island Quarry was identified as a suitable material for LCAP. Conventional new asphalt pavements have an SRI of about 0, and weathered asphalt pavements have an SRI of about 6. This paper describes the importance of LCAP technology in reducing the heat island effect, the benefits of using it, required testing, and practical development of a LCAP mix.
Over the past 25 years, Alberta Transportation (AT) has collected successive datasets of Falling Weight Deflectometer (FWD) deflection data over their 21,000 km (almost entirely flexible) highway network. A study was conducted to investigate the variation in back calculated subgrade modulus between two or more test dates in different collection years using AT’s FWD inventory data. Presently, AT uses the AASHTO 1993 method for the design of flexible pavement rehabilitation. The AASHTO 1993 design method only applies a temperature correction to the FWD central deflection, which is not directly used for estimated subgrade support strength, and therefore does not account for subgrade strength variation as a function of temperature at the time of testing. This paper presents a subgrade modulus temperature correction model developed from the FWD inventory data. The model was able to reduce the variation of subgrade modulus by a statistically and practically significant amount. If implemented, the model can be incorporated into the pavement rehabilitation design method to either minimize the risk of an under-designed pavement from using a higher than typical back calculated subgrade modulus, or minimize the risk (added costs) of over-design from using lower than typical back calculated subgrade modulus.
TRB's E-Circular 232: Automated Vehicle Symposium 2017: Summary of a Symposium highlights the themes from an event that took place on July 11–13, 2017 in San Francisco, California. The report follows the general symposium agenda. The presentations by speakers in the general sessions are summarized, including the highlights from the 25 breakout sessions. A list of the posters presented in two sessions is provided. The appendices provide a description of the key topics covered in the breakout sessions.
Bloomington Road, Regional Highway 40 in the Regional Municipality of York, serves as a major artery for vehicles accessing Highway 404. The section under review between Kennedy Road and Highway 48 was built in 1969 and rehabilitated with an innovative pavement design in 2005. Prior to rehabilitation, the asphalt surface was severely oxidized with extensive thermal cracking, however, the longitudinal and transverse profiles of the roadway were in relatively good condition and there was no sign of major structural failures. Rehabilitation of the roadway consisted of Cold In-Place Recycling (CIR), a Heavy-Duty Asphalt Binder Course (HDBC) Hot Mix Asphalt (HMA), and a 6.7 mm rut-resistant fine-graded Stone Mastic Asphalt (SMA). This paper provides a review of the design and construction details for the pavement lifts, as well as material and process selection details. Special consideration is given to the curing of the CIR and the rut resistance of the SMA lift. This paper also presents a long-term field performance evaluation of the rehabilitated pavement section with quantified in-situ performance by means of field observations, laboratory evaluations of retrieved pavement specimens, and semi-automated pavement performance data survey collected by York Region over twelve years of in-service pavement life.
Evaluation of the moisture damage of HMA is normally conducted on loose aggregate coated with binder or on HMA compacted samples; both methods having their respective disadvantages. Those tests are empirical and are susceptible to give misinterpretation of moisture damage. The complex modulus test for asphalt mixtures, also known as the dynamic modulus, characterizes the mixtures Linear Visco-Elastic (LVE) properties. This paper presents a method used at LCMB to evaluate the moisture damage of HMA samples based on LVE measurements. Two reference mixtures and three mixtures with glass aggregates were tested. One set of samples contained hydrated lime as an anti-stripping additive. First, the LVE properties of the samples were evaluated in a dry condition. Then, the samples were saturated with water and cured into a water bath at 60 deg C for 14 days and evaluated again. Overall, complex modulus test is very effective at evaluating the moisture damage of asphalt samples. This method has multiple advantages and many analysis options, which make it very interesting to evaluate moisture damage. Moreover, it was found that hydrated lime is a very effective anti-stripping additive. For some of the mixtures with anti-stripping agent, water soaking had little effect on the LVE properties.
There is no consensus among state highway agencies as to the appropriate binder specifications required for adequate quality control and acceptance of modified binders. Supplemental tests have been adopted in addition to standard Performance Grade (PG) tests and are often referred to as “PG+” procedures. The Multiple Stress Creep and Recovery (AASHTO M332) test has been proposed to replace the AASHTO M320 for PG grading of binders. However, some agencies are concerned that asphalt binder formulation will change after adopting the new system, while others are unsure how to relate the current M320 grades to the new S, H, and V grades. In this study, testing of a large number of binders was completed and correlations between results of “PG+” test and MSCR tests were performed. Regarding the MSCR test, results show that the %R parameter is a good candidate to detect the presence, and potentially the quantity, of elastomeric modification. However, using universal limits for the MSCR %R parameter that are dependent on Jnr values in not practical nor useful since current binder formulations are controlled differently by agencies. Furthermore, no logical equivalency of M320 PG grades to M332 traffic grades was identified, so changes to binder formulations are anticipated.
Premature cracking of flexible pavements is a very common problem in Canada. Nowadays, it is common to use several types of additives and modifiers to asphalt binders and asphalt mixes to improve their performance and increase the service life of flexible pavements. In order to mitigate pavement cracking, the asphalt mixes used in the pavement structure need to have a high resistance to fatigue or thermal cracking according to their position in the pavement structure. Several studies reporting on the use of fibers in asphalt concrete have been found in the literature. The objective of this project is to study the impact of the addition of Pulp Aramid Fiber (PAF) to Hot Mix Asphalt (HMA) in terms of mix design and indirect tensile strength. The optimum asphalt content of the fiber mixes is first determined and then the impact of fiber on their volumetric properties is investigated. Finally, the behavior of PAF in HMA is characterized by indirect tensile testing at different conditions. PAF mixes showed better ductility, even at lower temperatures, than the control mix. Therefore, PAF would lead to an improvement of the resistance to low temperature cracking and would delay crack propagation in the mix.
Nova Scotia Transportation and Infrastructure Renewal (NSTIR) implemented its pavement management system (Highway Pavement Management Application or HPMA) in 2008. NSTIR conducts annual pavement condition surveys on their highway network. Data collected includes International Roughness Index (IRI), which is used to calculate a Roughness Index (RI). Surface distress data is also collected to calculate a Distress Index (DI). The RI and DI are combined into an overall Pavement Quality Index (PQI). In 2016, NSTIR initiated a project to review their pavement prediction models. Differences in historical data trends were noted during the initial model review. These differences were thought to be a result of technological advancements in data collection equipment. The study examined the existing roughness and distress indices to determine if and/or how changes in data collection technology have impacted the measured pavement condition. The investigation included a review of the historical roughness and distress data. Based on this data review, changes were made to the roughness and distress models to better reflect current NSTIR data and conditions. A feedback analysis was then conducted on the prediction models to conduct performance modeling on the HPMA. This paper details the data investigation and updated models.
Alberta Transportation has completed rehabilitation of a number of highway sections using Cold In-place Recycling (CIR) and Full Depth Reclamation (FDR) over the years. In order to better understand the mechanism responsible for the formation of transverse cracks (specifically to see if transverse cracks are reflecting from the underlying pavement) and the susceptibility of the recycled material to moisture induced damage, Alberta Transportation retained Tetra Tech to undertake pavement inspections and analysis of selected projects rehabilitated using CIR and FDR. A total of five highway segments rehabilitated with CIR and one highway segment rehabilitated with FDR were included in the study. The study included a review of background information, visual crack mapping, pavement inspection using Ground Penetrating Radar, asphalt pavement coring, determination of moisture content in the CIR portion of the cores, and visual assessment of the cores to identify the progression and type of cracks. The key objectives were to investigate the performance of the pavements rehabilitated with CIR in terms of transverse crack formation and moisture susceptibility. This paper discusses the completed evaluation and findings from the study and further expands on Alberta Transportation’s experience with CIR, as presented at the 2016 CTAA Conference.
The British Columbia Ministry of Transportation and Infrastructure (MoTI) has been using 100 percent Reclaimed Asphalt Pavement (RAP) to pave numerous side roads in its network for more than 15 years with mixed results. The RAP is typically transported off site and recycled by adding a rejuvenator and processing the material through a pugmill. The cold recycled mix is then transported to site and placed using conventional paving equipment as a wearing surface – a surfacing layer of Hot Mix Asphalt (HMA) is not placed. Although the BC MoTI has been using this procedure for over a decade, no study to evaluate the addition rate of the rejuvenator, mix design, recycling process, or testing to determine the quality of the recycled mix was ever completed. The crushed granular equivalency or structural layer coefficient of the recycled mix was also never developed. This paper will document the findings of a laboratory program undertaken to evaluate the optimum addition rate of the rejuvenator, curing period prior to the placement of the recycled mix, and compaction criteria, as well as the structural layer coefficient and crushed granular equivalency of the recycled RAP. A case history of several previously completed projects using cold recycled RAP pavement are also presented.
Asphalt binders produced at refineries are becoming stiffer due to an ever-increasing demand for more expensive lighter and heavier fraction products such as gasoline, jet fuel, and lube oils. To increase output of lighter fractions and heavy gas oils, refineries have gone through upgrades producing higher amounts of stiffer asphalt binders such as Vacuum Distillation (VD) tower, Solvent De-Asphalting (SDA), and Residuum Oil Super critical Extraction (ROSE) unit bottoms. Materials used to soften/repair stiff asphalt binders are known as fluxes. Through recent work at Iowa State University, great potential was seen for epoxidized plant oil materials as fluxes/rejuvenators. Within this work two epoxidized plant oil products derived from soybeans, EBS and EMS were manufactured and used for modifying three stiff asphalt binders produced from VD tower, SDA and ROSE units. A full Superpave binder investigation found that improvement in low temperature performance was greater than improvement in high temperature performance for the SD and ROSE unit bottoms when using either EBS or EMS. It was also found that substantial decreases in costs, fuel usage, and emissions could be gained through the use of EBS and EMS in the production of asphalt mix.
The Regional Municipality of York, in collaboration with Metrolinx (an agency of the Government of Ontario), has implemented Bus Rapid Transit (BRT) lanes along the three most heavily travelled roads in York Region. To enhance visibility and assist motorists when navigating this new transit system, a special red-coloured asphalt mixture was employed as a surface layer. The colour was achieved by using a selected aggregate bland, colouring pigment, and specially formulated asphalt mixture. This paper provides information on steps employed in the design of coloured asphalt mixture such as: 1) selection of performance graded asphalt cement suitable for the Region’s climatic conditions and traffic loadings, 2) designing an aggregate blend to match the desired colour, ) performing a volumetric analysis for the special Hot Mix Asphalt to meet physical requirements of Superpave 12.5 FC2, and 4) performance testing to capture the impact of pigment on the mixture’s strength and durability at different in-service temperatures. Performance testing was performed at the Centre for Pavement and Transportation Technology located at the University of Waterloo. Production and paving experience with the coloured asphalt mix are also included in this paper, as well as field performance in terms of manual and automated distress survey.
Currently in progress, the “Regina Bypass” highway project involves the construction of approximately 45 km of a new four-lane highway (greenfield), the rehabilitation of more than 18 km of Highway 1 (brownfield), and 5 km of reinforcement works on an existing section. The project is being realized using a “Design-Build-Finance-Operate-and-Maintain” (DBFOM) approach and it will be operated by the concessioners group until late October 2049. Taking into account the specific physical and climatic constraints involved, as well as the concession’s duration, flexible pavements have been designed using several innovative concepts such as a mechanistic pavement design approach to the structural pavement design, the use of engineered asphalt mixes, the use of on-site recycling process for existing sections, and the installation of performance monitoring stations. This article provides a summary of the numerous laboratory tests required for the study of the engineered asphalt mix formulations specifically developed for this project, and it describes the follow-up program that will measure their performance with time.
Flooding has been identified as the most frequently occurring natural hazard in Canada. Extreme weather events, such as floods and extreme precipitation events, are increasing in intensity and frequency under climate change. The impact of flooding on asphalt pavements has become a rising concern, since pavements are designed based on historical data, which do not adequately reflect current and future climate. Therefore a comprehensive understanding of the flooding impacts o pavements is of great importance for improving their resilience. The objective of this study is to establish an assessment framework for the impacts of flooding on asphalt pavements through fragility analysis, and conduct case study to illustrate the approach. Flood characteristics, pavement damage patterns, damage components, and performance impact factors are investigated. Thirty-six extreme precipitation scenarios with various magnitudes, durations, and numbers of event cycles are loaded to two typical asphalt pavement structures in Southern Ontario by using MEPDG. Then, a probabilistic pavement fragility modeling method is developed for generating fragility functions, which integrate flood hazards, pavement structure, pavement performance, and damage states. Results show that the loss of pavement life is not negligible due to extreme events. Fragility functions and curves are able to demonstrate the probability of exceeding certain pavement damage given flood hazards.