TAC Transportation Intelligence

Safety
Evaluation of safety and operational impacts of bicycle bypass lanes at modern roundabouts
Modern roundabouts have been found to improve safety and reduce overall delay, but they may have negative impacts on the safety of cyclists as other vehicles may cut-off cyclist paths while entering or exiting the roundabout. Several before–after studies have found an increase in traffic collisions involving cyclists at roundabouts after being converted from conventional signalized intersections. Another concern associated with roundabouts is the safety of pedestrians, especially pedestrians with severe vision impairment who may find difficulty in negotiating roundabouts. This paper evaluates safety and operational impacts of using bicycle bypass lanes at roundabouts as a means of increasing the safety of cyclists. The paper also recommends the full utilization of pedestrian traffic signals, proposed by other studies, by incorporating them with the proposed bicycle bypass lanes. An evaluation scheme involving the safety benefits and the costs of the proposed bypass lanes is provided to help practitioners decide when they are warranted. The evaluation scheme is illustrated using an application example. (Canadian Journal of Civil Engineering, October 2008, pp. 1025-1032)

Roadside Memorials and Traffic Safety
Roadside memorials, the makeshift shrines erected near the sites of traffic fatalities, are becoming more common throughout North America and the world as a public expression of grief and a way for mourning family and friends to deal with their loss. The practice has also been roundly criticized by those who claim roadside memorials simply distract drivers and create road hazards. Tay's study shows that the markers appear to have significant short-term safety benefits. As part of his study, he placed mock-up memorials at selected intersections with red light cameras within the City of Calgary. In the six weeks after the markers were installed, nearly 17 percent fewer drivers ran red lights than in the six weeks prior to installation. (R. Tay, University of Calgary, 2008, 17 p.)

Environment

Temporary Bridging to Avoid or Minimize Impacts to Waters and Wetlands During Highway Construction
Road construction or maintenance work near waterways has the potential to create unintended environmental impacts. Typical practice has involved the use of culverts or riprap in or across streams to create detours or provide access to the site for equipment and personnel. However, this approach discharges fill and, as a result, requires environmental permitting. The use of temporary bridging is an alternative that can save time and money while minimizing or avoiding impacts on the environment. In this study, the research team reviewed relevant regulations, types of temporary bridging, and factors influencing the use of temporary bridging. A decision matrix was then developed, providing a straightforward set of criteria to assist in selecting the most appropriate alternative. This digest will be useful for any transportation professionals involved in the design, construction, or maintenance of road facilities in proximity to waters and wetlands. (TRB's National Cooperative Highway Research Program Research Results Digest 330, September 2008, 25 p.)

Smart Transportation Guidebook: Planning and Designing Highways and Streets that Support Sustainable and Livable Communities
In conjunction with the New Jersey Department of Transportation (NJDOT) and the Pennsylvania Department of Transportation (PennDOT), the Delaware Valley Regional Planning Commission (DVRPC) has commissioned the preparation of the Smart Transportation Guidebook. Smart Transportation can be summarized in six principles: Tailor solutions to the context, Tailor the approach, Plan all projects in collaboration with the community, Plan for alternative transportation modes, Use sound professional judgment, and Scale the solution to the size of the problem. The book provides guidelines for improving the roadway system in accordance with Smart Transportation principles. It should be used in the planning and design of non-limited access roadways of all classifications, from principal arterial highways owned by the state government to local roadways. (Delaware Valley Regional Planning Commission, March 2008, 92 p.)

Structures

Continuous condition assessment of highway bridges using field monitoring
The ageing and deterioration of highway bridges can have serious consequences in terms of reduced safety and serviceability. The objectives of this paper are to present an approach for the structural health monitoring of concrete bridge structures; and to demonstrate the effective use of field monitoring data for the updating of service life prediction models, which accuracy can be significantly improved. A case study on a major highway bridge is also presented and used to illustrate the approach. (INFRA 2008, Novemeber 2008, 13 p.)

Structural behaviour and design criteria of under-deck cable-stayed bridges and combined cable-stayed bridges. Part 1: Single-span bridges
This paper examines two new types of bridges, namely under-deck cable-stayed bridges and combined cable-stayed bridges, for prestressed concrete road bridges with single-spans of medium length. Both bridge types offer many advantages over conventional schemes in several aspects, such as structural efficiency, enhanced construction possibilities, and both economic and aesthetical considerations. They are very slender structural types with a very high structural efficiency, for which the materials used in the deck are reduced to one third of that in conventional bridges without stay cables. In this paper, the most important aspects of the structural behaviour of these bridge types are set out through the description of a careful selection from an extensive collection of bridges designed and analysed by the authors in a previous research project. In addition, a detailed set of design criteria for these bridge types is presented, based on the results of the extensive parametric study undertaken in the aforementioned research project. (Canadian Journal of Civil Engineering, September 2008, pp. 938-950.)

Structural behaviour and design criteria of under-deck cable-stayed bridges and combined cable-stayed bridges. Part 2: Multi-span bridges
This paper deals with the application of under-deck cable-staying systems and combined cable-staying systems to prestressed concrete road bridges with multiple spans of medium length. Schemes using under-deck cable-staying systems are not suitable for continuous bridges, as they are not efficient under traffic live load and only allow for the compensation of permanent load. However, combined cable-staying systems are very efficient for continuous bridges and enable the design of very slender decks (1/100th of span) where the amount of materials used is halved in comparison with conventional schemes without stay cables. In this paper, the substantial advantages provided by combined cable-staying systems for continuous bridges (such as high structural efficiency, varied construction possibilities, both economic and aesthetical benefits, and landscape integration) are set out. Finally, design criteria are included. (Canadian Journal of Civil Engineering, September 2008, pp. 951-962.)

Pavements

Use of nondestructive testing to establish mechanistic-based seasonal load-carrying capacity of thin-paved highways in Saskatchewan
It has long been known that increased load-carrying capacity during the winter months is very beneficial to rural road transportation in Saskatchewan. However, it has been observed that rapid weakening of thin-paved roads during spring thaw is highly detrimental to the load-carrying capacity of these roads. Direct measures of the structural integrity of Saskatchewan roads as a function of seasonal changes have not been quantified in the past. The objective of this study was to directly quantify the impact frost action has on the load-carrying capacity of thin-surfaced roads. This study examined the magnitude and rate of change of in situ structural deflection responses of a typical Saskatchewan thin-surfaced road during fall freeze-up and spring thaw in 2006–2007. This study showed that structural deflection responses significantly improved with frost depth greater than 50 cm and that deflection response significantly worsened with minimal thaw depth, as expected. The data obtained also indicated a significant increase in nonlinear strain weakening behavior during fall freeze-up at frost depths less than 50 cm. Therefore, based on the findings of this study, the frost thickness and the rate of change in frost thickness need to be directly considered in the fall and in the spring when calculating seasonal load limits of thin-paved roads. (Canadian Journal of Civil Engineering, July 2008, pp. 708-715.)

Effects of Seasonal Changes on Ride Quality at MnROAD
This project studied frost heave as it relates to different pavement design parameters and ride quality deterioration. Elevations of frost pins embedded in MnROAD test sections were measured over four years. Pin elevation changes were analyzed to show the amount of frost heave and degree of frost heave uniformity within a cell. Various plots were made to show the elevation change and interquartile range of the pins over time. Statistical approaches such as visual analyses, Student-t hypothesis testing, and ANOVA analysis were used in this study to evaluate the effect of pavement design features on frost heave and roughness. The effects of frost heave on ride quality deterioration for flexible and rigid pavements could not be confirmed or statistically rejected in this study. (Minnesota Department of Transportation Report 2008-23, July 2008, 137 p.)

Traffic

New approach to determine number of lanes on freeway upgrades
A slow-moving heavy vehicle can substantially reduce traffic flow because the vehicle acts as a moving bottleneck. In particular, the bottleneck can be initiated on a long uphill freeway section where heavy trucks gain little acceleration and propagate upstream when the percentage of loaded trucks in the traffic is high. This paper finds an interesting relation between the bottlenecks and some physical factors including heavy vehicle characteristics, road geometry, traffic flow theory, and percentage of trucks in traffic. According to this relation, the paper provides two dimensionless physical parameters to characterize the formation and propagation of the queues initiated by loaded trucks on uniform upgrades, respectively. Based on the critical values of these parameters aforementioned, the paper can help transportation engineers to determine that the number of design lanes under the conditions that the growing bottlenecks initiate along upgrade section cannot be resolved by simply using equations and rules suggested in the 2000 edition of the Highway capacity manual. (Canadian Journal of Civil Engineering, October 2008, pp. 1033-1041.)

Evaluating new methodologies for estimating performance on two-lane highways
This paper examines two new methodologies for field estimation of percent time spent following (PTSF) on two-lane highways. Using speed and time headway data, the two methodologies estimate the percentage of vehicles trapped in platoons, unable to pass slow-moving vehicles. A total of 236 h of field data, including individual speeds and headways, were collected at three study sites in the state of Montana. The study examined the sensitivity of PTSF estimates to some important platooning variables. The study also included a comparison of PTSF estimates from the new methods versus those found using the current United States National Research Council Highway capacity manual (HCM) analytical procedures. Study results showed that the two new methodologies were successful in capturing the effect of platooning variables on PTSF estimates and outperformed the HCM procedures in this regard. Further, the results strongly attest to the promise of the proposed methods in advancing the current analytical procedures for estimating performance on two-lane highways. (Canadian Journal of Civil Engineering, August 2008, pp. 777-785.)

Determining Effective Roadway Design Treatments for Transitioning from Rural Areas to Urban Areas on State Highways
This report reviews an Oregon research effort to identify ways to calm operating speeds as the vehicles transition into developed suburban/urban areas from rural roads. Drivers of vehicles approaching the urban environment have few visual cues to reduce their speeds until their vehicles are well into the more urban environment. This report specifically reviews a simulator study for rural-to-urban transitions. The study included two pilot studies and one full scale study. (Oregon Department of Transportation Research Report SPR 631, September 2008, 192 p.)

Safety

Evaluation of accident prediction for rural highways
This paper evaluates the accuracy of three commonly used models that predict accidents on two-lane, rural, arterial highways. The retrospective evaluation compared model outputs with empirical collision results for a sample of highway sections in the Province of New Brunswick. The analysis determined historical accident rates, identified key predictive variables, and compared the observed results with estimates from each safety model. All three models were found to significantly overestimate accident frequencies on the highway sections under study. The model generally employed in New Brunswick, MicroBENCOST, was found to yield the highest errors in estimated collisions. These findings suggest that the benefits from accident reduction are generally overestimated on highway improvement projects analyzed with these accident prediction models. (Canadian Journal of Civil Engineering, June 2008, pp. 647-651.)

Evaluation of The Applicability of The Interactive Highway Safety Design Model To Safety Audits of Two-Lane Rural Highways
The Interactive Highway Safety Design Model (IHSDM) is a suite of software developed by the Federal Highway Administration (FHWA) for monitoring and analyzing two-lane rural highways in the United States. Among the six modules available in IHSDM, two were chosen for evaluation because of their applicability to audit safety of the two-lane rural highways in Utah, namely the Crash Prediction Module (CPM) and the Intersection Review Module (IRM). Based on the findings of the study, it is concluded that the CPM and IRM of IHSDM could be a useful tool for engineering decision-making during safety audits of two-lane rural highways. However, the outputs from these modules demand knowledge and experience in highway design. (Utah Department of Transportation Report UT-08.02, March 2008, 154 p.)

Towards Zero: Ambitious Road Safety Targets and the Safe System Approach
This is a summary of the report Towards Zero: Ambitious Road Safety Targets and the Safe System Approach. The purpose of the report is to review the state of the art in improving road safety performance and examine the role of targets in raising the level of ambition and achieving effective implementation of road safety policies. The work aims to assist governments in raising the performance threshold by developing more systematic approaches to road safety. It highlights the institutional management changes required in many countries to implement effective interventions through a strong focus on results and underlines the economic case for road safety investment. This summary document comprises the recommendations, executive summary and table of contents of the full report together with details of the experts that contributed to the work. (OECD International Transport Forum Summary Document, 2008, 28 p.)

Transportation Intelligence

Volume 6 Number 6

December 2008

Environment

Structures

Pavements

Traffic

Safety

Feedback

Environment

Structures

Pavements

Traffic

Safety