  Highway on-ramps are regarded as typical bottlenecks in transportation
networks. In previous work, mainline vehicles' selfish lane choice behavior at
on-ramps is studied and regarded as one cause leading to on-ramp inefficiency.
When on-ramp vehicles plan to merge into the mainline of the highway, mainline
vehicles choose to either stay steadfast on the current lane or bypass the
merging area by switching to a neighboring lane farther from the on-ramp.
Selfish vehicles make the decisions to minimize their own travel delay, which
compromises the efficiency of the whole on-ramp. Results in previous work have
shown that, if we can encourage a proper portion of mainline vehicles to bypass
rather than to stay steadfast, the social traffic conditions can be improved.
In this work, we consider employing a proportion of altruistic vehicles among
the selfish mainline vehicles to improve the efficiency of the on-ramps. The
altruistic vehicles are individual optimizers, making decisions whether to stay
steadfast or bypass to minimize their own altruistic cost, which is a weighted
sum of the travel delay and their negative impact on other vehicles. We first
consider the ideal case that altruistic costs can be perfectly measured by
altruistic vehicles. We give the conditions for the proportion of altruistic
vehicles and the weight configuration of the altruistic costs, under which the
social delay can be decreased or reach the optimal. Subsequently, we consider
the impact of uncertainty in the measurement of altruistic costs and we give
the optimal weight configuration for altruistic vehicles which minimizes the
worst-case social delay under such uncertainty.

Systems and Control;Systems and Control