Research Brief

The construction and maintenance of new infrastructure is not always the best way of confronting congestion. In many cases, it is much less expensive to design policies that shift traffic to underutilized infrastructure. The Getting the Goods without the Bads: Freight Transportation Demand Management Strategies to Reduce Urban Impacts (CFIRE 07-02) project, led by CFIRE affiliate researcher Joel Rogers, analyzed a variety of techniques for re-allocating freight and maximizing the use of existing infrastructure while also reducing the social costs of transportation. These techniques are known as freight transportation demand management (TDM) strategies.

This project consisted of in-depth analyses of a variety of TDM strategies, focusing on how each satisfies different goals, including reduced emissions, congestion reduction, reduced fuel consumption, and increased freight accessibility. These strategies fit into eight categories:

  • Anti-idling policies
  • Designated truck routes
  • Modal shift
  • Changing delivery hours
  • Intelligent Transportation Systems (ITS)
  • Land-use planning
  • Parking policies
  • Planning information coordination

Most of the freight TDM strategies analyzed in this project were found to be generally beneficial to communities wishing to confront transportation issues without resorting to additional construction. In general, planning information strategies and parking policies have the potential to provide significant benefits at a very low cost, and are among the least likely to incite community opposition.

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General effectiveness of various TDM strategies: note that success is dependent on the unique circumstances of each city

The high costs and likelihood of unanticipated consequences of two of these strategies, however, make them unlikely to provide net benefits to their communities. Promoting modal shift from truck to rail is difficult for the public sector, given the many factors in private sector logistics decisions, and, if effective, is likely to upset residents living near rail facilities. In addition, additional freight rail traffic often leads to more trucks on the road. Similarly, restricting truck traffic during nighttime hours, while it can reduce some nighttime noise, is likely to exacerbate regional peak period congestion.

To learn more about this project and to read the final report, visit the CFIRE 07-02 project page.

Proper pavement texture is crucial to prevent road accidents, especially in wet conditions, but there are currently no minimum friction requirements in US road design. This is due mostly to the cost and difficulty of direct friction measurement that would be needed to confirm such requirements. This project proposes that friction, as well as noise emissions and energy usage, can be ascertained cheaply and non-destructively through lab testing of the asphalt mix.

The Characterizing Rider Safety in Terms of Asphalt Pavement Surface Texture (CFIRE 07-08) project, led by CFIRE affiliate researcher Hussain Bahia, aims to evaluate how asphalt mixes affect friction test results in the lab, and how well these predictions translate to the field. If these relationships are reliable, then specifications can be issued to improve rider safety while designing asphalt mixes.

In the field, friction is measured by a simple friction number (FN), assessed through a locked-wheel test. In the lab, the surface of an asphalt sample was measured by its mean depth profile (MDP), which is assessed by a surface laser-profilometer (SLP). Although cumbersome in the field, the use of an SLP in the lab would make asphalt analysis much simpler, and relating the asphalt’s MDP to its FN would give meaningful data to the designers who wish to achieve a minimum FN.

In addition, this project developed a model for predicting lab results, including MDP, from asphalt design parameters. The model used data from the Wisconsin Highway Research Program (WHRP) and the Minnesota Department of Transportation pavement test track facility. One of the most significant factors was found to be the variation in aggregate size used in the asphalt.

In this project, it was found that there was a high level of correlation between MDP and FN, which meant that friction performance of asphalt could be estimated from lab results. In addition, a model developed from asphalt mix results showed that the lab results were correlated to mix parameters such as the gradation of asphalt materials. Combining these two results gives a method for estimating road friction from mix design, which can be used to enhance highway safety.

To learn more about this project and to read the final report, visit the CFIRE 07-08 project page.

 

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