Adjacent lane dependencies modulating wave velocity on congested freeways-An empirical study

Much of traffic flow theory and highway design is based upon the fundamental relationship, FR, between speed, flow, and density. Traditionally, the FR is assumed to be a static curve over time and space. This paper presents new empirical findings that show the FR in one lane of a freeway can actually change shape in a rapid and systematic response to conditions in the adjacent lanes. This paper demonstrates the dependencies for a general purpose freeway lane that is operating in the congested regime. The drivers become more conservative in response to slower speeds in either adjacent lane, conversely, they become less conservative in response to higher speeds in either adjacent lane. It is also shown that as drivers become more conservative the signals and waves move upstream slower. So this inter-lane dependency has a direct impact on how fast signals propagate through the traffic stream. For the study site the empirical relationship between the wave speed and relative speed is close to linear. This interdependence between lanes is an important factor that it is absent from most traffic flow and car following models. Given these findings the discussion explores hypothetical examples showing how the inter-lane dependencies can give rise to mechanisms for waves in adjacent lanes to synchronize, as well as a mechanism for a queue spreading from one lane to another without any lane change maneuvers. Finally, this work closes with an exploration of the possible physiological mechanisms that might be occurring in the drivers. (c) 2020 Elsevier Ltd. All rights reserved.