Gianluca Dell'Acqua

Road Performance Evaluation Using Geometric Consistency and Pavement Distress Data

Many studies on driver speed behavior are found in the scientific literature today, and various researchers have addressed roadway alignment consistency for travel safety in the context of current operating speeds. An experimental analysis of low-volume roads without spiral transition curves between geometric tangent and circular elements on the horizontal alignment was conducted in southern Italy. All selected roadways are located in areas with level terrain and vertical grades of less than 6%. This study is a continuation of a 2009 research project that developed procedures to predict speed factors for horizontal curves and tangents on low-volume roads. The present research focuses on the design of continuous operating speed profiles that reproduce real driver speed behavior at each section of the horizontal alignment with variables that now include the pavement deterioration condition. Four new regression equations were developed to predict the operating speed on tangent and circular curve elements by using speed factors and geometric variables. These models were developed by a traditional ordinary least-squares method involving speed values not surveyed in transition zones. The aim of this refined study is to illustrate the roadway factors influencing optimal and safe driving performance.

Safety Data Analysis to Evaluate Highway Alignment Consistency

Road safety has become a priority field worldwide and one of the major factors describing the state of the transport system with its positive and negative changes. Many studies on driver speed behavior can be found in the scientific literature, and researchers have addressed roadway alignment consistency for travel safety in the context of real operating speeds. This study illustrates an experimental analysis conducted on the Tirrenia Inferiore State Highway in southern Italy without spiral transition curves between geometric tangent and circular elements on the horizontal alignment in order to check a new prediction consistency model. Two consistency measures were developed and compared with the results available in the literature: the first was the relative area bounded by the speed profile and the average weighted speed, and the second was the standard deviation of operating speeds in each design element along the entire road examined. With a combination of these two previous measures and according to an extensive sensitivity analysis, a consistency model was developed and thresholds for good, acceptable, and poor road consistency can now be proposed. The consistency prediction model was related to the number of crashes occurring between 2003 and 2010. It was found that as design consistency increased, the number of crashes decreased significantly. The consistency model can be used for this purpose during the geometric design process or during the evaluation process for two-lane rural highways.

Indirect Skid Resistance Measurement for Porous Asphalt Pavement Management

This paper focuses on developing a method for road managers to assess the sideways-force coefficient (SFC) in porous asphalt with low-cost standard tests. SFC can be used as a component in road surface condition surveys and asset management decisions. A standard piece of equipment for determining SFC is the sideways-force coefficient routine investigation machine (SCRIM), which can be truck or trailer mounted. This equipment is often beyond the budget of most small, low-volume road agencies. An empirical model for the indirect estimation of SFC for porous road surfaces was developed as a result of this study. With handheld equipment—the portable skid resistance tester [to derive the British pendulum number (BPN)] and the sand patch method [height in sand (HS) test]—a correlation of these test results can be made, and a reasonable approximation to SFC with the use of the SCRIM method can be attained. BPN, the unit of measurement of the skid tester, is a representation of the microroughness of the wearing surface, and the sand patch method (HS test) results yield the macroroughness of the pavement. The study was conducted over 20-km segments of low-volume roadway in southern Italy. The initial results are promising, with a maximum percentage of error of less than 15.2%. Further study is needed to adapt the model to other road surface conditions.

Models of Operating Speeds for Low-Volume Roads

Recent studies have documented a noticeable disparity between the speeds for which roads are designed and the actual operating speeds. An important reason for driving errors on two-lane rural roads is the misjudgment of the real course of the road by road users. Unfavorable visibility conditions are one of the problems of road infrastructure that can be detected on existing low-volume roads. Therefore an operating speed model was developed to calculate the contribution made by sight distance, and to be a useful tool for planners in the study of the safety of existing roads. Seven low-volume roads in the province of Salerno, Italy, were studied. The study identified operating speeds on 84 curves; the relative sight distance, radius, radius of the previous curve, length of the tangent before the curve, curvature change rate, development of the curve, and number of speed changes made during the study were determined for each curve. Because of the different characteristics of the roads analyzed, once the data were collected it was possible to develop two operative speed models. The first was suitable for roads characterized by consecutive curves alternating with small tangents and the second model was mainly intended for roads characterized by a small number of curves that were preceded and followed by long tangents.

Procedure for Making Paving Decisions with Cluster and Multicriteria Analysis

For many years, much research has been carried out to assess the affordability of paving a road. Now, increased construction and maintenance costs for traditional asphalt pavement systems have persuaded many civil administrations, regional councils, and agencies to replace pavement with gravel surfaces. Low-volume roads (LVRs), as they are presented in this paper, constitute a significant proportion of the total road network in Italy (around 80%) and in many other countries. Such infrastructures are vital parts of the road network, but their construction can have significant adverse effects on the environment. As a result, these roads must be well planned, well designed, well constructed, and properly maintained to create minimal adverse effects, to be cost-effective in the long term, and to have acceptable maintenance and repair costs. Limited resources often exist for LVRs, and a frequent question is whether to use paved or gravel surfaces. In many cases, the choice depends only on economic considerations, which must take maintenance costs into account. A complete procedure that applies cluster analysis and multicriteria analysis is presented for deciding whether to pave gravel road surfaces on the basis of different geometric, traffic, and environmental layouts.

Safety performance functions for crash severity on undivided rural roads

The objective of this paper is to explore the effect of the road features of two-lane rural road networks on crash severity. One of the main goals is to calibrate Safety Performance Functions (SPFs) that can predict the frequency per year of injuries and fatalities on homogeneous road segments. It was found that on more than 2000km of study-road network that annual average daily traffic, lane width, curvature change rate, length, and vertical grade are important variables in explaining the severity of crashes. A crash database covering a 5-year period was examined to achieve the goals (1295 injurious crashes that included 2089 injuries and 235 fatalities). A total of 1000km were used to calibrate SPFs and the remaining 1000km reflecting the traffic, geometric, functional features of the preceding one were used to validate their effectiveness. A negative binomial regression model was used. Reflecting the crash configurations of the dataset and maximizing the validation outcomes, four main sets of SPFs were developed as follows: (a) one equation to predict only injury frequency per year for the subset where only non-fatal injuries occurred, (b) two different equations to predict injury frequency and fatality frequency per year per sub-set where at least one fa tality occurred together with one injury, and (c) only one equation to predict the total frequency per year of total casualties correlating accurate percentages to obtain the final expected frequency of injuries and fatalities per year on homogeneous road segments. Residual analysis confirms the effectiveness of the SPFs.

Calibrating the passenger car equivalent on Italian two line highways: a case study

AbstractThe Level of Service (LOS) of a road infrastructure, a concept introduced for the first time in the Highway Capacity Manual (second edition), is defined as the ‘qualitative measure of traffic conditions and their perception by users’. The Highway Capacity Manual, developed in the U.S., is still the most highly internationally credited reference text in the study of vehicular traffic. The method proposed by the Highway Capacity Manual is based mainly on studies and research compiled in the U.S., so in order to apply this method to other realities (e.g. Italy), research needs to be carried out at a local level. In this study, a series of studies were carried out to verify the transferability of these procedures to two roads classified as ‘two-lane highways’. Two fixed RTMS (Remote Traffic Microwave Sensor) were used to record traffic data for two sections located at 3100 km on the SP30 and at 8900 km on the SP175 from 1 January to 31 December 2010. From the data, it was possible to determine not onl...

Operating Speed Prediction Models for Sustainable Road Safety Management

Road safety management may be improved if quantitative assessment of safety levels is carried out. One of the most frequent roadway characteristics that affect crashes is the geometric alignment. Many highway design standards in the world have introduced rules to assess the alignment consistency. In this paper we report an experimental analysis conducted in 2010 on statistically significant number of roadway sections belonging to two - lane rural highways in Northern Italy. The aim of this research is to develop operating speed prediction models on tangents and circular curves. Acquired relationships were particularly interesting and different explanatory variables were introduced in the predictive models which are dependent on examined geometric roads features. These relationships constitute a new set of models about the operating speeds to design and verify geometric highways alignments adding to those already available in the scientific literature.

Assessing Transferability of Highway Safety Manual Crash Prediction Models to Data from Italy

For decades, crashes have been studied as discrete events with the focus on the circumstances of the crash. This type of analysis has been used to identify the characteristics of roadway features associated with higher crash experience, but other factors, such as traffic volumes, driver characteristics, land use, and environmental conditions, are also needed to explain or describe crash events. The Highway Safety Manual (HSM) provides a predictive method to estimate the expected average crash frequency of a site in given geometric and geographic conditions over a specific period for a specific annual average daily traffic volume. The study presented here investigated whether the modeling results closely matched the crash records. The HSM algorithms were used to assess transferability as a whole. The results suggested that implementing the HSM techniques should foster the development of local safety performance functions and accident modification factors. Calibration preserved the original HSM model form and the relationship between independent variables and crashes. To adjust the base predicted crash frequency to meet the current conditions, the accident modification factor calculations for lane width, horizontal curves, and vertical grades were made. Crash types (head-on and side collisions, single-vehicle crashes, and rear-end collisions) were investigated on the basis of the vertical grade and the curvature indicator. The estimated model provides planners and designers with a tool better able to target and select countermeasures to address these specific aspects and results in improved project selection and improved safety.