Gabriel Valdez

Valuing Public Sector Risk Exposure in Transportation Public-Private Partnerships

A methodological framework can be used to evaluate public revenue financial risk exposure when transportation infrastructure is delivered through public–private partnerships (PPPs) in the United States. Transportation agencies worldwide and across the United States are increasingly using PPPs as a mechanism to deliver infrastructure. An analysis of international experience conducted for this research shows that countries with more extensive experience in PPPs than the United States have devised sophisticated methodologies to value and manage risk exposure in the context of value for money and optimum allocation of project risks. However, a review of major U.S. transportation PPP transactions reveals that U.S. states currently lack a well-documented methodology to quantify and incorporate the cost of public-sector risk into the evaluation of PPP projects. This evidence suggests that U.S. transportation agencies might benefit significantly from implementing more systematic approaches to incorporate the cost of risk in the evaluation of PPP projects. The framework proposed in this research provides a step-by-step methodology to quantify revenue risk exposure and is aimed at facilitating the estimation of the risk-adjusted costs of delivering a project as a PPP. The methodology is based on the concept of contingent liabilities and uses option pricing techniques. The application of the methodology is demonstrated by two U.S. transportation PPP case studies.

Applying Dynamic Modeling Methods to IH 35 Through Austin: Exploring Options for Addressing Future Congestion

ABSTRACT The City of Austin is among the fastest-growing cities in the U.S., with the surrounding counties keeping a similar pace. Travel times from downtown Austin to Round Rock, where many commuters live, currently range from 45 to 60 minutes during the average afternoon rush hour. Decision-makers have expressed a need to examine long-term solutions for IH 35 to explore concepts discussed under previous studies. This study applied dynamic traffic assignment coupled with static and dynamic tolling analysis, user class restrictions and multi-class simulation and assignment to examine various long-term scenarios with potential to address growing congestion on this critical corridor. The findings were illuminating: if residential and employment growth continue on their current pace through 2035, the region wide dynamic traffic assignment results applied at the mesoscopic level in this study demonstrate that Central Texas faces a grim future of extreme traffic congestion on IH 35. While an added capacity scenario was identified which can address future IH 35 congestion in some instances, it is of questionable viability for implementation. The scenario with the largest capacity addition did not provide the best results due to limited accessibility and only when the limits were extended dramatically, did researchers find more positive congestion relief. However, this scenario would be the highest investment and would probably be deemed infeasible simply due to cost. A more positive finding was that a hybrid strategy of added capacity, dynamic tolling, and travel demand management solutions demonstrates even greater benefits. When all options were considered, it was realized that added capacity would not be enough; it would need to be coupled with managed lanes, changes in travel behavior, more efficient land use, demand management and increased transit use.

Estimating Vehicular Emission Impact of Nighttime Construction with VISSIM and Different MOVES Emission Estimation Approaches

Shifting work zones from daytime to nighttime is a potential solution to air quality issues on roadway with high traffic volume and where it is undesirable to close lanes during peak hours. The expected benefit of such shifting is to reduce total fuel consumption and on-road vehicle emissions. However, the magnitude of emission reductions and air quality impacts has not been examined comprehensively at work zones. The study presented in this paper investigated the traffic-related emission impacts of work zones using an urban freeway case study. A VISSIM test bed combined with the Environmental Protection Agency’s MOVES emission model was used to estimate total emissions assuming daytime and nighttime lane-closure scenarios. Vehicle emissions were estimated using a link-based method and operating mode-based method. The results from both methods demonstrated that nighttime construction has a significant impact on both traffic speeds and vehicle emissions, primarily as a result of reductions in vehicle miles traveled. In addition, a horizontal comparison between the results from the two methods was made to assess the impact of different emission estimation approaches. The outcomes from the comparison highlight the potential importance of the operating mode-based approach for accurately estimate total traffic emission quantities when data or simulations are available.

Multiresolution visualization tools to aid in conducting road safety audits

Typical road safety audits use site investigations in addition to historical data to make recommendations. Recent approaches have used simulation modeling to derive surrogate measures to analyze the potential for collisions, driving simulators to analyze human behavior, or other visualization tools to analyze geometric design characteristics. None of these tools can capture the dynamics of proposed changes that subsequently alter traffic patterns. Each proposed improvement has an influence on traffic patterns and must be captured at a regional level to determine whether vehicles choose the same path or defer to an alternative one. This study explored new methods to supplement the Road Safety Audit process. The study used visualization tools to assess the performance of each proposed improvement strategy by conducting a more thorough comprehensive safety study with multiresolution modeling methods in situations when suggested countermeasures would almost certainly redistribute traffic to alternative routes. A case study was selected in which an audit team performed a safety audit of a diamond interchange in El Paso, Texas, that experienced a high number of collisions during peak hours. The visualization of the proposed improvement scenarios helped the Texas Department of Transportation understand better how mitigation strategies would influence traffic flow in and around the study area or whether the proposed changes improved safety or merely shifted the problem to alternative locations. The use of visualization tools can help convey proposed improvements to the public.