Roadway Width Research Articles

Composite (steel–concrete) highway bridge fatigue assessment

Steel and composite highway bridges are currently subjected to dynamic actions with variable magnitudes due to the action of vehicles crossing on the deck pavement. These dynamic actions can generate the nucleation of fractures or even their propagation in the structures. Depending on the magnitude and intensity, these adverse effects can compromise the structural system response and the reliability which may also lead to a reduction of the expected bridge service life. A composite (steel–concrete) bridge with a 12.50 m roadway width and 0.23 m concrete deck thickness, spanning 40.0 m by 13.5 m was investigated in this work. The computational model, developed for the composite bridge dynamic analysis, adopted the usual mesh refinement techniques present in finite element method simulations, and was implemented in the ANSYS program. The proposed analysis methodology and the procedures presented in the design codes were initially assessed to evaluate the bridge fatigue response in terms of its structural service life. The stress cycle counting techniques and the cumulative damage rule application had been analyzed through S–N curves, based on an extensive revision of steel and composite bridges’ service life and theoretical fatigue aspects in steel structures. The investigation also considered the recommended procedures used for the steel and composite structures’ main codes. The main conclusions of this paper focused on alerting structural engineers to the possible distortions, associated with the steel and composite bridges’ service life when subjected to vehicles’ dynamic actions.

Microsimulation Study of Effect of Volume and Road Width on PCU of Vehicles under Heterogeneous Traffic

The traffic volume and roadway capacity are the important basic inputs required for planning, analysis, and operation of roadway systems. Expressing traffic volume as number of vehicles passing a given section of road or traffic lane per unit time will be inappropriate when several types of vehicles with widely varying static and dynamic characteristics are comprised in the traffic. The problem of measuring volume of such heterogeneous traffic has been addressed by converting different types of vehicles into equivalent passenger cars and expressing the volume in terms of passenger car unit (PCU) per hour. The vehicles of highly heterogeneous traffic such as the one prevailing on Indian roads may occupy any convenient lateral position on the road, based on the availability of space, without any lane discipline. This study is concerned with the estimation of PCU values of vehicles in such traffic conditions, using microscopic simulation. The PCU values obtained for different types of vehicles, for a wide range of traffic volume and roadway conditions, indicate that the PCU value of a vehicle significantly changes with change in traffic volume and width of roadway.

A Bayesian semi-parametric model to estimate relationships between crash counts and roadway characteristics

This paper uses a semi-parametric Poisson-gamma model to estimate the relationships between crash counts and various roadway characteristics, including curvature, traffic levels, speed limit and surface width. A Bayesian nonparametric estimation procedure is employed for the model’s link function, substantially reducing the risk of a mis-specified model. It is shown via simulation that little is lost in terms of estimation quality if the nonparametric estimation procedure is used when standard parametric assumptions (e.g., linear functional forms) are satisfied, but there is significant gain if the parametric assumptions are violated. It is also shown that imposing appropriate monotonicity constraints on the relationships provides better function estimates. Results suggest that key factors for explaining crash rate variability across roadways are the amount and density of traffic, presence and degree of a horizontal curve, and road classification. Issues related to count forecasting on individual roadway segments and out-of-sample validation measures also are discussed.

Evaluation of Highway Design Parameters on Influencing Operator Speeds through Casewise Visual Evaluation

Designing highways to influence driver operating speed effectively through environmental feedback is a key research field requiring special attention. Virtual reality video simulations were used to record the influence of environmental elements on driver judgments about the appropriate driving speed. This study evaluated the use of various means that could affect operating speeds and affect driver behavior without compromising safety. Data were analyzed through the fuzzy set nonlinear modeling system of Casewise Visual Evaluation methodology to identify design factors that most strongly influenced perceived operator discomfort. The findings indicated that vegetation type and density and barrier type have a significant effect on driver discomfort and thus have the potential to influence operating speeds. Roadway width has a similar effect where narrower roadways increase driver discomfort. The results indicate that roadside features and certain road design elements can be used to affect driver operating speeds.

Vision-Based Roadway Geometry Computation

Geometric data in transportation, such as roadway geometry, are important for asset management and for safety analysis. Traditional roadway geometric data are measured in the field, which is time consuming, costly, and dangerous. This paper proposes an algorithm to compute roadway geometric data, including roadway length, lane width, line width, and pavement marking size, from images. This paper makes two major contributions. First, the paper proposes a generalized roadway geometry computation algorithm using emerging vision technology based on two-dimensional (2D)/three-dimensional (3D) image reconstruction. The proposed algorithm consists of four steps, which are camera calibration from vanishing points, roadway vanishing line computation, homography computation and 2D/3D reconstruction, and, finally, roadway geometry computation. Second, the paper develops an error model, called roadway geometry error model (RGEM), to spatially quantify and visualize computation errors so that decision makers can choose measurement locations with an acceptable error. The geometric interpretation to RGEM is also presented in terms of roadway vanishing line. The proposed algorithm has been tested using two sets of images that were collected from the Georgia Tech campus and from actual video log images provided by the Georgia Department of Transportation. The roadway geometry was computed and the computation errors were analyzed. The test results show that the computation errors increase when the computation locations approach the roadway vanishing line. For the computation location with a distance of 190 pixels to the roadway vanishing line, the pavement lane width computation error is less than 3 cm. The experimental results also demonstrate that the proposed error model, RGEM, is able to reliably evaluate the roadway geometry computation errors. Applications of the proposed algorithm for modern and intelligent transportation system are also discussed.

Object-oriented methodology for intersection simulation model under heterogeneous traffic conditions

In developing countries like India, the traffic on roads is highly heterogeneous in nature, with vehicles of widely varying static and dynamic characteristics. In this type of traffic, vehicles do not follow lane discipline and they move freely over the entire width of roadway based on availability of space. To study this type of complex traffic flow and associated vehicular interactions, simulation is considered as an effective tool. An object-oriented methodology (OOM) for heterogeneous traffic simulation is proposed in this paper with focus on mid-block and intersection flow modeling. The paper presents the basics and advanced features of object-oriented programming (OOP) in detail in the context of traffic flow. The sample C++ code is discussed in detail to demonstrate the implementation of OOP features, such as encapsulation, inheritance and polymorphism. The contribution of this research work is the development of software objects for various components such as vehicle, traffic, link and node. This software can be adopted for heterogeneous traffic simulation programs, in general.

Collision Prediction Models for Three-Dimensional Two-Lane Highways

Collision prediction models for three-dimensional (3-D) alignments of two-lane rural highways are lacking in the literature. This paper presents such models with vehicle collision data on 5,760 km (3,600 mi) of two-lane rural highways in Washington State collected from 2002 through 2005. Five statistical models were developed for different combinations of 3-D alignments to establish the relationship between collision frequency and the relevant variables. The alignment combinations are (a) horizontal curves combined with crest vertical curves, (b) horizontal curves combined with sag vertical curves, (c) horizontal curves combined with multiple vertical curves, (d) horizontal curves combined with grades of less than 5%, and (e) horizontal curves combined with grades of more than 5%. For each combination, four different statistical techniques were explored: Poisson, negative binomial, zero-inflated Poisson, and zero-inflated negative binomial. For validation, two models were selected and estimated by using the first 3 years of collision data and validated with the last-year data. The results show that the most significant predictors for collisions on horizontal curves on 3-D alignments are the degree of curvature, roadway width (lanes plus shoulders), access density, product of grade value and grade length, road section length, and average annual daily traffic. The results of this study should be useful in evaluating road safety on 3-D alignments and optimizing their design based on the substantive safety approaches.

Development and Evaluation of an Adhesively Bonded Panel-to-Panel Joint for a FRP Bridge Deck System

A fiber-reinforced polymer (FRP) composite cellular deck system was used to rehabilitate a historical cast iron thru-truss structure (Hawthorne St. Bridge, Covington, VA). The most important characteristic of this application is reduction in self-weight, which raises the live load-carrying capacity of the bridge by replacing the existing concrete deck with an FRP deck. This bridge is designed to HL-93 load and has a 22.86 m clear span with a roadway width of 6.71 m. The panel-to-panel connections were accomplished using full width, adhesively (structural urethane adhesive) bonded tongue and groove splices with scarfed edges. To ensure proper construction, serviceability, and strength of the splice, a full-scale 2-bay section of the bridge with 3 adhesively bonded panel-to-panel connections was constructed and tested. Results showed that no crack initiated in the joints under service load and no significant change in stiffness or strength of the joint occurred after 3,000,000 cycles of fatigue loading. The proposed adhesive bonding technique was installed in the bridge in August 2006.

Longest bi-directional road tunnel planning for phased construction in Korea

The bi-directional road tunnel longest in Korea is to be constructed in Baehooryung area as part of Korea National Road 46. It is a single tube tunnel with a length of 5,057 meters in two lanes including service tunnel along its full length with cross passages at every 180 meter interval connecting both tunnels. One more tunnel will be supposed to be constructed at the location of the service tunnel for proposed road extension to four lanes (two one-way tunnels) in uncertain future. The tunnel plan focused on its safety from fire and the road extension work. Due to the tunnel length, traffic direction and uncertainty about extension, a fully-transverse ventilation system and a spacious roadway shoulder width are adopted for this tunnel. In this project, the service tunnel is multi-purposely used for the pilot tunnel during the main tunnel excavation, the emergency evacuation route in tunnel fire, and the enlargement excavation in future extension work. This paper introduces a very long road tunnel with very poor traffic condition and describes its safety measurements from tunnel fire and phased construction plan. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. “Reprinted with permission from Elsevier”.

Influence of Parapets and Aspect Ratio on Live-Load Distribution

Significant discrepancies in girder distribution factors have been observed between actual bridge field-testing results and AASHTO code predictions. One of the reasons for the discrepancies is that code methods fail to account for the existence of secondary members such as parapets in bridges. This research investigates the effects of parapets and bridge aspect ratio on live-load moment distribution for bridge girders. The influence on distribution factors of parapets with varying overhang lengths and of aspect ratio with varying roadway width is investigated. To study the effects of parapets and aspect ratios, 34 two-span continuous bridges with a 0° or a 45° skew angle and with varied structure parameters are analyzed using the finite element method. The distribution factors obtained from these analyses are compared with those from the AASHTO methods. The presence of parapets is shown to reduce distribution factors by as much as 36 and 13% for exterior and interior girders, respectively. The effect of parapets is slightly less for skewed bridges. Aspect ratio is shown to have very little effect on distribution factors until the ratio exceeds 1.8.

Florida DOT Project-Level Bridge Management Models

The Florida Department of Transportation (FDOT) is in the process of implementing Pontis, a Bridge Management System, to provide decision support to engineers in the headquarters and district offices as they make routine policy, programming, and budgeting decisions regarding the preservation and improvement of the state's bridges. As part of this effort, an ongoing research program is underway to adapt the system to FDOT needs as well as to advance the state of the art in several areas important to the Department. Most of the research results are organized around a new project-level decision support framework that complements and builds on Pontis' existing network-level analysis. Specific new models include accident risk and user cost due to roadway width and alignment deficiencies; user cost of load capacity and vertical clearance restrictions, and moveable bridge openings; project-level prediction models for bridge element condition and costs; and prediction of economics of scale and scoping possibilities. The new models are built into a highly graphical spreadsheet model for decision support use.

Design Optimization Study of a Three-Span Continuous Bridge Using HPS70W

Since its introduction to the bridge market in 1996, High Performance Steel (HPS) has been successfully implemented in a wide range of bridge projects by several state transportation departments. Examples of which include the Snyder South Bridge in Nebraska that was initially designed using AASHTO M270 Grade 50 weathering steel. The Nebraska Department of Roads opted to use HPS70W in place of the Grade 50 weathering steel without performing any redesign. This was done to provide information on welding and fabrication issues with HPS70W (Wasserman, Azizinamini, Pate and Greer, 1998). Also, in 1996, the Tennessee Department of Transportation (TDOT) partnered with FHWA through the Innovative Bridge Research and Construction Program to use HPS70W in a bridge project. The TDOT was in the process of designing a two-span continuous bridge, with span lengths of 236 ft 6 in., located on Tennessee State Route 53 over Martin Creek (FHWA, 1998). The bridge has a roadway width of 28 ft on three I-girders spaced at 10-ft 6-in. The superstructure was redesigned utilizing HPS70W for the girders and Grade 50W steel for the stiffeners, cross-frames, and other miscellaneous steel. The designs were performed using the 1994 AASHTO LRFD Bridge Design Specifications. These bridges are reported to have cost savings on the order of 10 percent through the inclusion of HPS70W in their superstructures. This paper presents a cost analysis of a fixed three-span bridge incorporating various material and girder configurations. An optimized parametric design study was conducted by varying key superstructure design variables. Girders are optimized in this study based on least weight for a fixed span-to-depth ratio.

Models relating traffic safety with road environment and traffic flows on arterial roads in Addis Ababa

This paper presents the study carried out to develop accident predictive models based on the data collected on arterial roads in Addis Ababa. Poisson and negative binomial regression methods were used to relate the discrete accident data with the road and traffic flow explanatory variables. Significant accident predictive models were found with a number of significant explanatory variables. The results show that the existing inadequate road infrastructure and poor road traffic operations are the potential contributors of this ever-growing challenge of the road transport in Addis Ababa. The results also indicate that improvements in roadway width, pedestrian facilities, and access management are effective in reducing road traffic accidents.

Selecting exposure measures in crash rate prediction for two-lane highway segments

A critical part of any risk assessment is identifying how to represent exposure to the risk involved. Recent research shows that the relationship between crash count and traffic volume is non-linear; consequently, a simple crash rate computed as the ratio of crash count to volume is not proper for comparing the safety of sites with different traffic volumes. To solve this problem, we describe a new approach for relating traffic volume and crash incidence. Specifically, we disaggregate crashes into four types: (1) single-vehicle, (2) multi-vehicle same direction, (3) multi-vehicle opposite direction, and (4) multi-vehicle intersecting, and define candidate exposure measures for each that we hypothesize will be linear with respect to each crash type. This paper describes initial investigation using crash and physical characteristics data for highway segments in Michigan from the Highway Safety Information System (HSIS). We use zero-inflated-Poisson (ZIP) modeling to estimate models for predicting counts for each of the above crash types as a function of the daily volume, segment length, speed limit and roadway width. We found that the relationship between crashes and the daily volume (AADT) is non-linear and varies by crash type, and is significantly different from the relationship between crashes and segment length for all crash types. Our research will provide information to improve accuracy of crash predictions and, thus, facilitate more meaningful comparison of the safety record of seemingly similar highway locations.

Absorptive Sound Barriers: Effects of Three Potential Changes to Current Design Standards of Virginia Department of Transportation

The Virginia Department of Transportation (VDOT) currently designs absorptive sound barriers with their entire face absorptive [noise reduction coefficient (NRC) of 0.8 or greater]. Using the FHWA Traffic Noise Model, the sound level increases caused by three modifications to current VDOT practice were investigated: a more reflective barrier surface (NRC = 0.7), a 6-in. (15-cm) reflective cap, and a 2-ft (61-cm) reflective base. These increases were computed for receivers up to 40 ft (12.2 m) above the ground and 1,000 ft (305 m) behind the barrier. The computations included three barrier locations—barrier opposite receivers, barrier same side as receivers, and barriers on both sides—at several barrier heights and distances from the roadway. They also included two roadway widths and two traffic conditions, to span the extreme ranges of these variables. Results indicate that for a barrier opposite the receivers, the more reflective surface caused a maximum increase of 1.3 dB, the 2-ft (61-cm) reflective base caused a maximum increase of 1.7 dB, and all three modifications combined inflated this increase to 2.7 dB. For a barrier on the same side of the roadway as the receivers, no situations caused increases greater than 1 dB. Finally, for barriers on both sides of the roadway, the more reflective surface caused a maximum increase of 1.1 dB, and all three modifications combined inflated this increase to 1.5 dB. A table of resulting sound level increases for the full field of computed receivers—for the worst-case situations encountered in the computations—is included.

Unit Power Density Evaluations of Roadway Lighting Systems

In accordance with the ANSI/IESNA American National Standard Practice for Roadway Lighting, RP-8-00, roadway lighting calculations were made to investigate Unit Power Density (UPD). Calculations were made for specific luminaires, roadway configurations and lighting system geometries, over both a range of mounting heights (Ht) and a range of overhang-setback distances (Oh). For each value of Oh, at each Ht, the luminaire cycle distance was increased until any one of the illuminance or luminance criteria are not met. The last distance that meets all the criteria (for both the illuminance and luminance methods) is the maximum for that run. As the mounting height was increased over successive runs, maximum distance consistently increased, before decreasing. Overhang-setback was initially set at the midpoint of its range and at least five adjacent values calculated, then additional variations as necessary to determine the maximum spacing. Optimum luminaire cycle distance typically occurred when the combination with height and overhang result in the uniformity and average criteria both reaching their limits. Both high pressure sodium (HPS) and metal halide (MH) sources were included in the calculations, including some in each of the four classifications of cutoff, and applied to roads of varied classifications (local, collector and major) and widths from one to six lanes. Results indicate that roadway lighting systems which meet both the illuminance and luminance criteria, have predictably lower UPD values with HPS lamps than with MH lamps. The best MH systems have UPD values 1.5 to 1.8 times the values for the best HPS systems applied to similar roadways. Systems that meet only the Luminance method criteria have significantly lower UPD values than systems which meet the criteria for the Illuminance method or both methods. In addition, as luminaire cutoff becomes more stringent, a system's UPD value tends to increase. Systems designed to the Luminance method and with luminaires with HPS lamps and semi-cutoff or non-cutoff distributions typically produce the lowest UPD values for a given roadway classification and width, but as roadways become wider the differences decrease. The increase in UPD when full cutoff is required is shown to be from 9 percent to more than 20 percent.

Factors influencing injury severity of motor vehicle–crossing pedestrian crashes in rural Connecticut

The ordered probit model was used to evaluate the effect of roadway and area type features on injury severity of pedestrian crashes in rural Connecticut. Injury severity was coded on the KABCO scale and crashes were limited to those in which the pedestrians were attempting to cross two-lane highways that were controlled by neither stop signs nor traffic signals. Variables that significantly influenced pedestrian injury severity were clear roadway width (the distance across the road including lane widths and shoulders, but excluding the area occupied by on-street parking), vehicle type, driver alcohol involvement, pedestrian age 65 years or older, and pedestrian alcohol involvement. Seven area types were identified: downtown, compact residential, village, downtown fringe, medium-density commercial, low-density commercial, and low-density residential. Two groups of these area types were found to experience significantly different injury severities. Downtown, compact residential, and medium- and low-density commercial areas generally experienced lower pedestrian injury severity than village, downtown fringe, and low-density residential areas.

User Cost Model for Bridge Management Systems

User cost models are used in bridge management systems to quantify, in economic terms, the potential safety and mobility benefits of functional improvements to bridges. One component of many such models is a formula to predict traffic accident risk on the basis of bridge characteristics such as roadway width and approach roadway alignment. A critical analysis of the user cost model used in AASHTO’s Pontis and Bridgit systems found that the model was overly sensitive to extremes of roadway width, yielding unrealistically high benefit estimates. A new model was developed using Florida data on bridge characteristics and traffic accidents. The new model has superior behavior and statistical characteristics on a full inventory of state highway bridges. Since it relies solely on National Bridge Inventory data items, the model is readily transferable to many different bridge management systems.

Modeling Congestion on Urban Roads and Assessing Level of Service

A unified methodology has been proposed for the quantification of congestion, incorporating the volume and operational characteristics of traffic movement. The level of congestion has been modeled to relate to the causal influences of traffic movement. Modeling congestion has provided a quantitative basis for understanding the contribution of different vehicle types in overall congestion, and it is useful for evolving the policy for congestion mitigation. Quantified congestion level has been used as a logical and improved measure of effectiveness to account for the conceptual definition of level of service in a quantitative manner. Based on the congestion level, 10 levels of service have been proposed, with 9 in a stable flow zone (presently designated as A–E), and 1 representing an unstable operation (presently designated as F). The philosophy has been demonstrated by developing congestion models and assessing the effect of roadway width on congestion levels and service volumes. While it is possible to assess the realized benefits from an increase in roadway width, the required number of traffic lanes for a desired level of service can also be estimated.

Wearing Surfaces for Orthotropic Steel Bridge Decks

In the state of Alaska, a six-span 884.5-m orthotropic steel bridge crosses the Yukon River at a 6 percent grade. The bridge is on a gravel road, it has a roadway width of 9.2 m, and the orthotropic steel deck is supported by two steel box girders 154.9 cm wide and 414.0 cm deep. The structure is expected to support the oil pipeline, a future gas line, and a low volume of heavy loaded trucks and to respond to harsh winter temperatures. This structure was designed in the early 1970s with a 127-mm two-layer timber deck wearing surface. Since then, the wearing surface has been replaced twice with timber decks (1981, 1992) and is again scheduled for timber deck replacement in 1999. Alternative wearing surfaces for other orthotropic bridge decks are reviewed. Orthotropic steel deck flexibility is examined and design charts for selecting the thickness for a given wearing surface are presented. The design charts account for truck loads and temperature change; no provision is made for traction or abrasion. The use of these charts is illustrated. Strains caused by prepositioned truck loads were measured in the orthotropic steel deck. The deck had a two-layer 127-mm timber wearing surface. These strains were compared by analysis. The results showed that the timber-deck system was stiff. Live load tensile strains and the range of strain were low; thermal stresses are expected to be high. Cold temperature thermal cracking, abrasion, adhesion to the steel deck, and traction are important parameters for selecting a future wearing surface. Live load fatigue in the wearing surface should not be a problem for this orthotropic bridge.