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Conditional priority is recognized as having the potential to improve transit service reliability at small cost to general traffic. The popular preference for conditional priority over unconditional priority encounters the challenges of various and challenging test scenarios. This paper makes a comparative analysis of unconditional and conditional priority in terms of intersection performance, based on the logic rule-based bus rapid transit signal priority (BRTSP), an active transit signal priority (TSP) for use at isolated signalized intersections with median bus-only lanes. Compared to previous study, the design of phase scheme, including two BRT phases, eight vehicle phases and four pedestrian phases, and the technical framework of BRTSP, centered on four categories of logic rules, have been improved to incorporate a mechanism for providing phase insertion, a special signal priority treatment in addition to green extension and early green. Phase insertion detector, if phase insertion is desired, is installed on the bus-only lane between check- in and check-out detector to trigger phase insertion request. A new category of logic rules, i.e., rules for early green response, is introduced into as a component of BRTSP to dynamically alter the response of the vehicle phases conflicting with the BRT phases to early green request. Inductive loop detector placed on each lane of the vehicle phases is used to monitor time headway and occupancy time on a lane by lane basis. The simulation experimental results indicated that: (1) phase insertion contributed substantially to late schedule deviations correction, but was recommended to be embedded in conditional priority rather than unconditional priority; (2) there was lack of convincing evidence that conditional priority had an inherent effectiveness of managing the intersection performance by varying the lateness criterion; (3) at TSP-enabled isolated intersections with green extension and early green, compared to having conditional priority, having an integration of unconditional priority and holding early BRT vehicles at control points may be a cost-effective solution not only to improve schedule adherence but also to accommodate the benefits of general traffic; and (4) at TSP-enabled isolated intersections with green extension, early green and phase insertion, there seemed to be a pressing need to move from unconditional priority to conditional priority. DOI: 10.1061/(ASCE)TE.1943-5436.0000179 CE Database subject headings: Buses; Rapid transit systems; Intersections; Traffic signals. Author keywords: Bus rapid transit; Median bus-only lanes; Isolated signalized intersection; Transit signal priority; Phase scheme; Logic rules.

At a certain point in the life of a flexible pavement, rehabilitation is required to improve pavement condition and to defer reconstruction. Pavement managers seek the best rehabilitation treatment on the basis of cost effectiveness. Using 1994-2002 data from a wet-freeze mid-Western state in the United States, this paper analyzes the cost effectiveness of four flexible pavement rehabilitation treatments: functional hot-mix asphalt (HMA) overlay, structural HMA overlay, resurfacing (partial 3R standards), and mill full-depth and asphaltic concrete overlay. The performance indicator used is the international roughness index and treatment effectiveness is measured in terms of performance jump (short-term), and service life and increase in pavement performance (long-term). The treatment cost is the equivalent uniform annual cost per lane-km incurred by the agency and user; and cost effectiveness is the ratio of effectiveness to cost. The study estimated treatment effectiveness under various combinations of traffic loading and climatic condition, and initial pavement condition. The results suggest that in the short-term, HMA structural overlay is the most effective treatment. For the long-term, the results are equivocal: HMA structural overlay is most effective from the perspective of average performance over the treatment life; resurfacing (partial 3R standards) is the most effective from the perspective of treatment service life. With regard to cost effectiveness, however, the results were consistent: for all three measures of treatment effectiveness, mill full-depth and asphaltic concrete overlay unequivocally appears to be the most cost effective treatment. Finally, the paper recommends that cost effectiveness analysis should be accompanied by a candid deliberation of project constraints, the local environment, and agency practices. DOI: 10.1061/(ASCE)TE.1943-5436.0000041 CE Database subject headings: Pavement management; Flexible pavements; Rehabilitation; Benefit cost ratios.

Many transportation agencies have started outsourcing maintenance activities to contractors by means of performance-based contracts. These outsourcing contracts are intended to transfer performance-based risk from transportation agencies to private contractors for a premium cost. Even though such contracts provide numerous benefits to both contractual parties, there are equally many concerns with their implementation. Certainly, one of the most important concerns is how to quantify performance-based risk. This paper presents a general and flexible framework for quantifying the performance-based risk in terms of premium cost for different contract specifications and preventive maintenance and rehabilitation strategies. The framework developed consists of three modular components: (1) the reliability-based pavement performance model; (2) the preventive maintenance and rehabilitation models; and (3) the pricing model. The developed framework is illustrated using the current design and rehabilitation methods for flexible pavements. DOI: 10.1061/(ASCE)0733-9364(2008) 134:7 (492) CE Database subject headings: Pavement management; Highway maintenance; Risk management; Contracts; Performance characteristics; Rehabilitation.

Advance warning signals are installed upstream of high-speed signalized intersections to warn motorists of impending signal changes. A new advance warning signal design was tested on an approach to a high-speed signalized intersection in Utah that utilized a dynamic blank-out sign with flashers mounted over the roadway. A state-of-the-art evaluation system was installed to collect continuous, nonintrusive data of vehicle speeds and red-light running events. Data were collected prior to and immediately after installation. Cumulative distributions of speed profile data showed statistically significant results after blank-out overhead dynamic advance warning signal (BODAWS) installation evidenced by an increase in mean speeds of 5-10 mph during the green interval, while the system was inactive, followed by a decrease in mean speeds of 5-10 mph after activation of the system. The system also reduced red-light running at the site during the time period immediately after BODAWS installation from five violations per million entering vehicles to one violation per million entering vehicles in the northbound direction, a statistically significant change using logistic regression. DOI 10.1061/(ASCE)0733-947X(2007) 133:10(564) CE Database subject headings: Radar; Traffic safety; Traffic speed; Traffic signals; Intersections.

The study reports on research that evaluated the impact of different types of left-turn phasing on older and younger drivers at high-speed signalized intersections. Using Poisson regression, the likelihood that a driver in a particular age group would be responsible for a left-turn crash under different types of phasing was evaluated. The induced exposure method was used to estimate exposure by age group. The variable of interest was left-turn crash rate for left-turning drivers who were responsible for circumstances contributing to the crash. Older drivers had higher crash rates than younger or middle-aged drivers for all types of phasing. Younger drivers had higher crash rates than middle-aged drivers for all types of phasing. All three age groups had the highest crash rate under protected/permitted and then permitted phasing within their respective age group. DOI: 10.1061/(ASCE)0733-947X(2007)133:10(556) CE Database subject headings: Traffic accidents; Regression analysis; Intersections; Traffic safety; Left-turns; Drive behavior.

The impact of left turns on operation is probably the most significant factor in the performance of conventional intersections. As a result engineers have looked to alternative measures for dealing with left turns at intersections to improve performance, some of which have been unconventional schemes. The purpose of this paper is to discuss an unconventional intersection scheme, the upstream signalized crossover (USC), which is a four-legged intersection designed to eliminate left turn opposing conflicts by crossing the left and through traffic to the left side of the road at all four approaches prior to the intersection. The crisscrossing of traffic upstream of the intersection results in four additional secondary signalized intersections. VISSIM was used to model and analyze the unconventional USC intersection as well as a conventional intersection for comparison. The analysis revealed that the USC intersection can handle higher traffic volumes at reduced overall delays. In terms of left turn delay, the conventional intersection performed better at lower volumes. However, the USC was able to handle much higher left turn volumes while maintaining acceptable level of delay. In terms of through movement delay, the USC intersection was found to perform significantly better than the conventional intersection. DOI: 10.1061/(ASCE)0733-947X(2006) (907) CE Database subject headings: Traffic signals; Intersections; Left-turns; Traffic management.

Seasonal deformation of unsurfaced roads was observed over several years and was studied using pavement deterioration models and finite-element analysis. The Mathematical Model of Pavement Performance is a model designed for pavement deterioration prediction and was successfully used for seasonal deterioration modeling because of its flexibility in defining the pavement structure, properties, and seasonal impact. However, these types of models are designed for highways and are somewhat limited in soils characterization and manipulation of the forces at the road-tire interface. Therefore, a three-dimensional dynamic finite-element model of a wheel rolling over soil was applied to simulate local vehicle traffic on a secondary unpaved road. These simulations were used to study the effects of vehicle speed, load, suspension system, wheel torque, and wheel slip on rutting and washboard formation. Modeling results are compared to field measurements and observations. CE Database subject headings: Deformation; Pavements; Deterioration; Finite element method.

This paper illustrates the field measurements of saturation flow headways and start-up lost times at 11 representative intersections in the state of Maryland. Based on those empirical results, this study has recommended two possible saturation flow rates and a maximum critical lane volume for use in intersection planning analysis that needs to reflect, to the extent possible, the behavior of Maryland's driving population. DOI: 10.1061/(ASCE)0733-947X(2005) 131:12(946) CE Database subject headings: Traffic management; Traffic flow; Flow rates; Maryland.

Road designers in Poland use capacity methods presented in subsequent issues of the Highway Capacity Manual (HCM). The new HCM 2000 gave an impulse for research aimed at evaluating adequacy of the default parameters of the HCM capacity models to the Polish conditions. Studies were conducted in several Polish towns and cities to investigate capacity of minor movements at two-way stop-controlled intersections, two-way yield-controlled intersections, and at roundabouts. The results have allowed developing equations of basic capacity parameters, i.e., critical time gap and follow-up time and calibrating the models to the local conditions. The paper presents these results and recommends how to adapt the HCM 2000 method to the Polish conditions. DOI: 10.1061/(ASCE)0733-947X(2005) 131:12(924) CE Database subject headings: Intersection; Traffic signals; Traffic management; Poland.

We give deterministic and stochastic models of the traffic on a circular road without overtaking. From this model the mean speed is derived as an eigenvalue of the min-plus matrix describing the dynamics of the system in the deterministic case and as the Lyapunov exponent of a min-plus stochastic matrix in the stochastic case. The eigenvalue and the Lyapunov exponent are computed explicitly. From these formulas, we derive the fundamental law that links the flow to the density of vehicles on the road. Numerical experiments using the MAXPLUS toolbox of SCILAB confirm the theoretical results obtained. Index Terms--Cellular automata, fundamental diagram, Lyapunov exponent, max-plus algebra.

Strong-post round-wood W-beam guardrail, G4(RW), is a common longitudinal barrier used in Texas. Recent crash tests on the system demonstrate its effectiveness in containing and redirecting a 2,000-kg pickup truck. Even though the guardrail performed satisfactorily according to National Cooperative Highway Research Program Report 350 requirements, there were concerns about the stability of the vehicle due to excessive wheel snagging on the posts. In this study, a modification to the existing design is evaluated to improve the stability of an impacting vehicle. LS-DYNA, a dynamic, nonlinear, large deformation finite element modeling code is used to analyze and compare the performance of alternate designs. A baseline finite element model of the existing system is developed to replicate the observed crash test behavior of the G4(RW). The fidelity of the baseline model is verified against full-scale crash test results. To improve the vehicle stability, the current design was modified to include guardrail posts with shorter embedment depth. An optimum post embedment depth was determined and used in the second simulation study. Finite element analysis results show that an improved G4(RW) system eliminates wheel snagging on posts, reduces sudden vehicle deceleration and therefore improves the stability of an impacting vehicle significantly. DOI: 10.1061/(ASCE)0733-947X(2005)131:1(63) CE Database subject headings: Guardrails; Energy dissipation; Deflection; Simulation; Finite element method.

A procedure for reconstructing run-off-road accidents into longitudinal W-beam guardrail systems was developed by estimating energy dissipation during an impact. Correlations were developed between the vehicle's departure angle, velocity, type of vehicle, and the energy dissipated. Energy losses are due to (1) barrier-vehicle friction: (2) post/soil deformations; (3) guardrail beam deformations, and (4) vehicle energy losses attributed to the vehicle (this is composed of actual vehicle damage and tire-ground friction, with vehicle damage being predominate). Barrier-vehicle friction losses were found to range from about 5 to 36%, depending upon speed and impact angle. The energy to cause permanent deflection of the guardrail posts in a system was found to be roughly, equivalent to the amount of energy dissipated by the rail deformation of that system. Comparisons with full-scale crash test results showed that the developed iterative reconstruction procedure accurately estimated impact velocities within 3%. DOI: 10.1061/(ASCE)0733-947X(2005)131:1(54) CE Database subject headings: Highway safety; Traffic accidents; Guardrails; Simulation; Barriers.

In this paper we address the problem of district design for the organisation of arc-routing activities. In particular, the focus is on operations like winter gritting and road maintenance. The problem involves how to allocate the road network edges to a set of depots with given locations. The collection of edges assigned to a facility forms a district in which routes have to be designed that start and end at the facility. Apart from the ability to support good arc routing, well-designed districts for road-maintenance operations should have the road network to be serviced connected and should define clear geographical boundaries. We present three districting heuristics and evaluate the quality of the partitions by solving capacitated arc routing problems in the districts, and by comparing the solution values with a multi-depot CARP cutting plane lower bound. Our experiments reveal that based on global information about the distribution system (ie the number of facilities or districts, the average edge demand and the vehicle capacity) and by using simple guidelines, an adequate districting policy may be selected. Keywords: districting; capacitated arc routing; heuristics; winter gritting

The paper presents an approach for roads detection based on synthetic aperture radar (SAR) images and road databases. The vectors provided by the database are refined using active contours (snakes). In this framework, we firstly develop a restoration filter based on the frost filter achieving an acceptable compromise between speckle elimination and lines preserving. This is followed by a line plausibility calculation step which is used to deform the snake from its initial location toward the final solution. The snake is reformulated using finite elements method. The setting of the snake parameters is not an obvious problem especially when they are tuned by trial-and-error process. We propose a new automatic computational rule for the snake parameters. Our approach is validated by a series of tests on synthetic and SAR images. Index Terms--Deformable models, finite elements, road database, roads detection, synthetic apeture radar (SAR) imagery, snakes parameterization, speckle reduction.

A method for predicting the traffic-load-induced settlement of road on soft subsoil with a low embankment is proposed. The traffic-load-induced dynamic stress in subsoil is calculated by the multilayer elastic theory (not covered in this paper). Then the plastic vertical strain in subsoil is calculated by an empirical equation, in which constants are related to the physical and mechanical properties of subsoil. The method was applied to analyze three different cases in Saga, Japan. Comparisons of the calculated values with field data indicate that the proposed method can provide a reasonable prediction of traffic-load-induced permanent settlement of the road on soft subsoil with a low embankment. The method is useful for designing the road with a low embankment on soft subsoil. For the cases studied with embankment thickness of 0.75 to 2.7 m, the depth significantly influenced by traffic load is about 6 m below the base of the embankments. DOI: 10.1061/(ASCE) 1090-0241 (2002) 128:11 (907) CE Database keywords: Embankment; Roads; Plastic deformation; Soil deformation; Soft soils; Deformation analysis.

People near British highways are willing to pay for attractive traffic calming measures to reduce noise and speed.

Research into the investment strategies for roads and highway schemes is given. This study examines the bias with adopting inefficient reference states as the basis for appraising road investments.

Byline: Paul Rouse (1), Martin Putterill (1), David Ryan (2) Keywords: Data Envelopment Analysis; highway maintenance; performance measurement; environmental factors Abstract: This paper describes the application of Data Envelopment Analysis (DEA) to a highway maintenance setting, using measures of inputs, outputs and outcomes reported by New Zealand local authorities. A general framework of performance measurement is developed and illustrated through application to the highway setting. The framework encompasses a performance pyramid embodying multiple-perspectives of the organisation with a structure of measures linking critical success factors to process drivers, methods of data analysis and influencing factors such as professional culture. Distinctions between measures of outcome, output and input enable finer partitioning of analyses into managerial notions of efficiency, effectiveness and economy. The impact of environmental factors on efficiency is explored through two approaches suggested in the literature. Author Affiliation: (1) Department of Accounting and Finance, The University of Auckland, Private Bag, Auckland, 92019, New Zealand (2) Department of Engineering Science, The University of Auckland, Private Bag, Auckland, 92019, New Zealand Article History: Registration Date: 29/09/2004

Byline: Kjell Ahlin, Johan Granlund, Fredrik Lindstrom Accurate road profiles are useful in vehicle design, such as for simulation of durability and ride quality. Laser/inertial profilometers typically record 1mm wide profiles. The question is how well such a profile matches perceived vehicle wheel roughness. The objective here was to create a more representative wheel track longitudinal profile. Simulated and measured wheel vibration was compared on a 6km long road. Simulations were made for several definitions of the profile. Results for single laser sensor profiles showed reasonable likeness to truck perceived roughness. By far the best likeness (14.5% better) was achieved when the profile was based on triangular 25%-50%-25% weighted data from three sensors in the wheel track. Clearly, vehicle engineers can benefit from using multiple laser profile sensors, instead of a single sensor. This will improve test accuracy, thus reducing vehicle design project lead times and costs.

Byline: Oldrich Kropac, Peter Mucka The longitudinal road profile is described by means of the power spectral density (PSD) and specified by two of its parameters, the unevenness index and waviness. This model with the waviness value equal to two is considered as the 'standard' model. Besides this statistically based model, two semi-empirical indicators of longitudinal road unevenness (roughness) are used: the International Roughness Index (IRI) and the wave-band triad consisting of three variances in three adjacent wavelength bands: short, medium, and long. In the first part of the paper, mutual conversion relations between the standard PSD and the other two indicators are given. The main emphasis of the paper is on considering gradual departures from the standard model. Firstly, general forms of waviness values different in partial wavelength bands are taken into account. Further attention is paid to the presence of periodic components in the longitudinal profile. Some other types of non-standard forms of longitudinal road profile are also briefly mentioned.