A model for holding strategy in public transit systems with real-time information

Holding strategies are among the most commonly used operation-control strategies in public transit systems. These strategies are most effective when used to control services characterized by high frequency. In this paper, a mathematical model for a holding control strategy is developed. Particularly, this model uses real-time information of locations of buses along a specified route. The objective of the developed model is to minimize the waiting time of passengers at all stops on that route. Furthermore, the model developed in this paper is characterized by the flexibility of adopting situations where bus occupancy could be either high, or low. A heuristic is developed to circumvent the complexity of the solution for the problem described. Numerical examples and computational results are presented and discussed.     

Mergers and innovation: evidence from a panel of US firms*

Mergers lead to larger firms and a less competitive market structure, but their effects on innovation are not clear. Mergers may improve innovation incentives by promoting economies of scope and scale, R&D activities, and increasing the ability to deal with uncertainties. However, mergers may also discourage innovation by reducing competition, increasing costs, and decreasing production and R&D efficiencies. In this study, we investigate merger impacts on innovation using a panel data consisting of four different data sets on publicly traded US manufacturing firms from 1980 to 2003. Our proxy for innovation is based on citation-weighted patent stocks. In our estimation model, we control for endogeneity using instrumental variables and factors such as market share, size, industry, and time. We find that mergers are positively and significantly correlated with firms’ innovation. Our findings also indicate that merger effect on innovation is heterogeneous across industries, increases with market share, and is greater in the long run. Our findings are robust to alternative measures of innovation.