Tolling Toward Congestion: The Jam-and-Harvest Effect and Its Equity Concerns

Dynamic tolling stands as a pivotal tool in contemporary highway management, aiming to balance traffic flow and generate sustainable revenue. Yet, a somewhat paradoxical outcome, the Jam-and-Harvest (JAH) phenomenon, has emerged. This research embarks on comprehensive investigation into this effect, dissecting its mechanisms via stochastic simulation, and laying bare the pressing equity challenges it inherently manifests.

At the heart of the JAH phenomenon is a sequence initiated by the operators' management to maximize revenues. By adjusting toll rates upwards, a sizable portion of the commuting vehicles gets deflected towards the unmanaged lanes. This diversion aggregates pronounced congestion, setting the stage for the actual traffic zenith. As this peak nears, the managed lanes, now vacant, contrast to the clogged unmanaged lanes, become increasingly attractive, resulting in revenue surge for the operators.

To lend empirical evidence to this observation, our research employs the stochastic simulation techniques. In the simulation model, we recreated realistic traffic dynamics, incorporating varying toll rates and mimicking diverse commuter decision-making patterns. These simulations offered a micro view of the Jam-and-Harvest strategy's tangible effects. Notably, results illuminated the stark congestion disparities between tolled and unmanaged lanes, providing quantifiable evidence of significant travel delay, extended total system travel times (TSTT) and disrupted commuter patterns. In addition, the equity challenge posed by the JAH effect is both profound and multifaceted. Through the simulated results, it became evident that commuters with a lower value of time (VOT) from the lower socio-economic group often appear in the congested unmanaged lanes, suffering much more severe travel delay.

In conclusion, the JAH phenomenon, while interesting when it first appeared, highlights the complex issues and possible problems with floating toll rate to maximizing profit. The immediate appeal of more revenue for operators is clear. However, the long-term structural, social, and economic implications brought to the fore by our detailed simulations advocate for a recalibration, especially as higher toll values and higher travel demand exacerbate disparities for lower income communities. Additionally, efforts should be made to optimize and possibly expand public transportation infrastructure, thereby reducing overall demand pressures on unmanaged lanes. This diversion could largely alleviate the gap and promote social fairness. Furthermore, setting caps or upper limit for toll price during peak hours can also promote equal access to routes, improving justice, equity and social fairness for all commuters.