Rural speed limit changes and safety

There is little information in the literature on the relation between rural speed and safety. The wide variation in rural speed limits that are applied in different countries tends to confirm that this relation is poorly understood. The changes in fatal, injury and all accidents that followed a change in the rural speed limit in seven countries were regressed against the change in vehicle mean speed. The results showed that speed significantly affects safety and that within certain limits the relation is linear. The regressions indicated that a 1 km/h reduction in speed will reduce all severities of accidents by between 4 and 5%. It is suggested that part of this reduction is due to a change in economic factors.     

高速公路改扩建工程车速限制方案研究

基于高速公路限速标准、限速方法以及改扩建高速公路的特征,围绕道路线形、特殊道路设施与事故率等方面着重分析了改扩建高速公路限速方案制定的依据及考虑因素,在符合相关法律法规的范围内提出适合我国改扩建高速公路限速研究及方案制定的思路及流程,并通过广东某改扩建高速公路的限速方案制定以详细介绍制定流程。     

道路汽车交通噪音的影响因素分析

道路交通噪声是交通噪声的主要部分。随着高速公路和高等级公路的迅速发展,车速提高,流量增加,道路交通噪声的影响也日趋突出。从汽车和路面两方面分析了影响道路汽车交通噪音大小的因素。     

Evaluation with sparse nominal data: The case of differential compliance with the 55 MPH limit

This paper notes the inability of analysts to evaluate the impact of certain policy interventions because of sparse nominal level data. Using the premise that knowing the limits of what could have happened will assist the investigator to know what did happen, this research enumerated all possible solutions or, in real world terms, scenarios that represent changes in driving behavior before and after the imposition of the 55 mph limit in 1974 on Michigan freeways. The enumeration tallied extreme values of all cells and some cell groupings in the 3x3 table representing the speed changes from 1973 to 1974. Enumeration of all possible solutions also yielded information about the likelihood that certain cells exceeded others. In some cases non-obvious and absolutely certain knowledge about interrelationships among some cells was uncovered. Substantively this investigation demonstrated that those 1973 drivers who travelled relatively fast modified their driving behavior more radically than those who were closer to the new 1974 speed limit.     

Optimal speed advisory for connected vehicles in arterial roads and the impact on mixed traffic

Connected Vehicles (CV) equipped with a Speed Advisory System (SAS) can obtain and utilize upcoming traffic signal information to manage their speed in advance, lower fuel consumption, and improve ride comfort by reducing idling at red lights. In this paper, a SAS for pre-timed traffic signals is proposed and the fuel minimal driving strategy is obtained as an analytical solution to a fuel consumption minimization problem. We show that the minimal fuel driving strategy may go against intuition of some people; in that it alternates between periods of maximum acceleration, engine shut down, and sometimes constant speed, known in optimal control as bang-singular-bang control. After presenting this analytical solution to the fuel minimization problem, we employ a sub-optimal solution such that drivability is not sacrificed and show fuel economy still improves significantly. Moreover this paper evaluates the influence of vehicles with SAS on the entire arterial traffic in micro-simulations. The results show that SAS-equipped vehicles not only improve their own fuel economy, but also benefit other conventional vehicles and the fleet fuel consumption decreases with the increment of percentage of SAS-equipped vehicles. We show that this improvement in fuel economy is achieved with a little compromise in average traffic flow and travel time.     

Nationwide survey on the posting of minimum speed limit signs on Interstate freeways

This paper presents the results of the mail out survey conducted in the United States to unveil the current state of practice related to the posting of minimum speed limit signs on Interstate freeway system. The analysis of the survey results has revealed that half of the country (25 states) posts the minimum speed limit on Interstate freeways. The most common posting is 40 mph. There are few states that post 45 mph and 55 mph in some sections on Interstate freeways. The survey results has also discovered that many states raised the maximum speed limits on Interstate freeways as the consequence of the National Highway System (NHS) designation Act of 1995 without revising or studying the effect of the existing minimum speed limits on traffic operation. Implications for future research relates to a multi state study which will evaluate the relevance of minimum speed limits on speed variability that is created by the posting of minimum speed limit.     

Dual influences on vehicle speed in special-use lanes and critique of US regulation

We verify that slow speeds in a special-use lane, such as a carpool or bus lane, can be due to both, high demand for that lane and slow speeds in the adjacent regular-use lane. These dual influences are confirmed from months of data collected from all freeway carpool facilities in the San Francisco Bay Area. Additional data indicate that both influences hold: for other types of special-use lanes, including bus lanes; and for other parts of the world.The findings do not bode well for a new US regulation stipulating that most classes of Low-Emitting Vehicles, or LEVs, are to vacate slow-moving carpool lanes. These LEVs invariably constitute small percentages of traffic; e.g. they are only about 1% of the freeway traffic demand in the San Francisco Bay Area. Yet, we show: that relegating some or all of these vehicles to regular-use lanes can significantly add to regular-lane congestion; and that this, in turn, can also be damaging to vehicles that continue to use the carpool lanes. Counterproductive outcomes of this kind are predicted first by applying kinematic wave analysis to a real Bay Area freeway. Its measured data indicate that the site selected for this analysis stands to suffer less from the regulation than will others in the region. Yet, we predict: that the regulation will cause the site’s people-hours and vehicle-hours traveled during the rush to each increase by more than 10%; and that carpool-lane traffic will share in the damages. Real data from the site support these predictions. Further parametric analysis of a hypothetical, but more generic freeway system indicates that these kinds of negative outcomes will be widespread. Constructive ways to amend the new regulation are discussed, as are promising strategies to increase the vehicle speeds in carpool lanes by improving the travel conditions in regular lanes.     

The location of two ring roads and the control of traffic speed which together minimises radial travel in a town

In a simple theoretical model, we seek the location of two ring roads which minimises the total radial travel in a circular town of unit radius. We assume that drivers choose least time paths and that the speed of vehicles is controlled so as to minimise radial travel. We show that, whatever the distribution of origins and destinations, if an internal ring road minimises the total radial travel then the radial traffic flow just inside the ring equals the radial traffic flow just outside the ring. We show that if origins and destinations are uniformly and independently distributed over that part of the radials within the town, and a circumferential ring road already exists, then the optimum radius of a single inner ring road is √2 − 1.     

Development of a corrected average speed model for calculating carbon dioxide emissions per link unit on urban roads

The purpose of our study is to develop a “corrected average emission model,” i.e., an improved average speed model that accurately calculates CO₂ emissions on the road. When emissions from the central roads of a city are calculated, the existing average speed model only reflects the driving behavior of a vehicle that accelerates and decelerates due to signals and traffic. Therefore, we verified the accuracy of the average speed model, analyzed the causes of errors based on the instantaneous model utilizing second-by-second data from driving in a city center, and then developed a corrected model that can improve the accuracy. We collected GPS data from probe vehicles, and calculated and analyzed the average emissions and instantaneous emissions per link unit. Our results showed that the average speed model underestimated CO₂ emissions with an increase in acceleration and idle time for a speed range of 20 km/h and below, which is the speed range for traffic congestion. Based on these results, we analyzed the relationship between average emissions and instantaneous emissions according to the average speed per link unit, and we developed a model that performed better with an improved accuracy of calculated CO₂ emissions for 20 km/h and below.     

Accounting for dynamic speed limit control in a stochastic traffic environment: A reinforcement learning approach

This paper proposes a novel dynamic speed limit control model accounting for uncertain traffic demand and supply in a stochastic traffic network. First, a link based dynamic network loading model is developed to simulate the traffic flow propagation allowing the change of speed limits. Shockwave propagation is well defined and captured by checking the difference between the queue forming end and the dissipation end. Second, the dynamic speed limit problem is formulated as a Markov Decision Process (MDP) problem and solved by a real time control mechanism. The speed limit controller is modeled as an intelligent agent interacting with the stochastic network environment stochastic network environment to assign time dependent link based speed limits. Based on different metrics, e.g. total network throughput, delay time, vehicular emissions are optimized in the modeling framework, the optimal speed limit scheme is obtained by applying the R-Markov Average Reward Technique (R-MART) based reinforcement learning algorithm. A case study of the Sioux Falls network is constructed to test the performance of the model. Results show that the total travel time and emissions (in terms of CO) are reduced by around 18% and 20% compared with the base case of non-speed limit control.     

High speed rail market projection: Survey design and analysis

This paper summarises work done to assess the market potential and likely financial performance of a planned high-speed rail link connecting Sydney, Canberra and Melbourne, under a variety of scenarios concerning the services offered and the possible market responses of the competing transport modes in the corridor. In the Australian context, such a link has the characteristics of an essentially new transport mode since existing rail services are extremely poorly developed. The expectation was that generated demand could be a substantial part of the overall ridership. A programme of market research was commissioned by the private consortium considering the project, designed to support forecasting models capable of predicting both diverted and generated travel on the new service. A major survey of current travellers was conducted in 1988, followed by an extensive collection of stated preference evidence about the factors affecting the travel decisions of both existing travellers and those who had not recently made any journeys in the corridor. The paper focuses mainly on the design and organisation of the surveys, on the analysis approach, and on the methods used to generate forecasts for simulated populations and scenarios.     

The use of patent analysis in assessing ITS innovations: US,Europe and Japan

A wealth of research on ITS has been carried out for the past two decades. In view of the rapid technological development and innovations occurring in ITS, the ITS stakeholders need to be aware of the usefulness and availability of patents associated with ITS technology. Among the national and international reviews which have been made available in journals of record and freely available public sources, little use has been made of patent information in assessing ITS innovations. Therefore, the paper looks at the ITS technology developments from the international perspective through utilizing rich, reliable information provided by ITS-related invention patents in the world’s three leading patent databases (EPO, USPTO, and JPO) to provide an overall picture of ITS innovations. The research findings show that the patent analysis can provide firms involved in the ITS sector and ITS researchers with information that can assist in their strategic planning efforts.     

Some comments on activity-based approaches to the analysis and prediction of travel behavior

This note presents the author's conjectures on several symptoms raised in Kitamura's assessment of activity-based travel analysis. It focuses on some of the characteristics of the development of activity-based approaches that may help explain their limited impact to date on travel demand forecasting practice. The broader role and potential contributions of activity analysis of the demand for infrastructure systems are emphasized.     

Preventing death and injury on the world's roads

The problem of deaths and injury as a result of road crashes is now acknowledged to be a global phenomenon with authorities in virtually all countries concerned about the growth in the number of people killed and seriously injured on their roads. The World Health Organization has declared that its annual World Health Day in 2004 will have the theme 'Safe Roads', and several organizations, including the World Bank and the Global Road Safety Partnership, are supporting this initiative to raise the profile of road safety in the public and political minds.     

A new probability statistical model for traffic noise prediction on free flow roads and control flow roads

A new traffic noise prediction approach based on a probability distribution model of vehicle noise emissions and achieved by Monte Carlo simulation is proposed in this paper. The probability distributions of the noise emissions of three types of vehicles are obtained using an experimental method. On this basis, a new probability statistical model for traffic noise prediction on free flow roads and control flow roads is established. The accuracy of the probability statistical model is verified by means of a comparison with the measured data, which has shown that the calculated results of L_eq, L₁₀, L₅₀, L₉₀, and the probability distribution of noise level occurrence agree well with the measurements. The results demonstrate that the new method can avoid the complicated process of traffic flow simulation but still maintain high accuracy for the traffic noise prediction.     

A microscopic analysis of speed deviation impacts on lane-changing behavior

Driving behavior models that capture drivers’ tactical maneuvering decisions in different traffic conditions are essential to microscopic traffic simulation systems. This paper focuses on a parameter that has a great impact on road users’ aggressive overtaking maneuvers and directly affects lane-changing models (an integral part of microscopic traffic simulation models), namely, speed deviation. The objective of this research is to investigate the impacts of speed deviation in terms of performance measures (delay time, network mean speed, and travel time duration) and the number of lane-change maneuvers using the Aimsun traffic simulator. Following calibration of the model for a section of urban highway in Tehran, this paper explores the sensitivity of lane-changing maneuvers during different speed deviations by conducting two types of test. Simulation results show that, by decreasing speed deviation, the number of lane changes reduces remarkably and so network safety increases, thus reducing travel time due to an increase in network mean speed.     

Explaining light vehicle demand evolution in interurban toll roads: a dynamic panel data analysis in Spain

Tolls have increasingly become a common mechanism to fund road projects in recent decades. Therefore, improving knowledge of demand behavior constitutes a key aspect for stakeholders dealing with the management of toll roads. However, the literature concerning demand elasticity estimates for interurban toll roads is still limited due to their relatively scarce number in the international context. Furthermore, existing research has left some aspects to be investigated, among others, the choice of GDP as the most common socioeconomic variable to explain traffic growth over time. This paper intends to determine the variables that better explain the evolution of light vehicle demand in toll roads throughout the years. To that end, we establish a dynamic panel data methodology aimed at identifying the key socioeconomic variables explaining changes in light vehicle demand over time. The results show that, despite some usefulness, GDP does not constitute the most appropriate explanatory variable, while other parameters such as employment or GDP per capita lead to more stable and consistent results. The methodology is applied to Spanish toll roads for the 1990–2011 period, which constitutes a very interesting case on variations in toll road use, as road demand has experienced a significant decrease since the beginning of the economic crisis in 2008.     

Estimating travel time functions for urban roads: options and issues

Travel time functions specify the relationship between the travel time on a road and the volume of traffic on the road. Until recently, the parameters of travel time functions were rarely estimated in practice; however, a compelling case can be made for the empirical examination of these functions. This paper reviews, and qualitatively evaluates, a range of options for developing a set of travel time functions. A hierarchy of travel time functions is defined based on four levels of network detail: area, corridor, route and link. This hierarchy is illustrated by considering the development of travel time functions for Adelaide. Alternative sources of data for estimating travel time functions are identified.

In general, the costs and benefits increase as the travel time functions are estimated at finer levels of network detail. The costs of developing travel time functions include data acquisition costs and analysis costs. The benefits include the potential for reducing prediction errors, the degree of application flexibility and the policy sensitivity of the travel time functions.