The inapplicability of current methods based on gap-acceptance theory for analyzing operational
conditions at not-conventional roundabouts (very frequent in urban areas) seriously hampers the
performance assessment; in practical applications, this also makes the choice of corrective design
measures very uncertain.
Starting from this considerations, the present paper shows the conceptual path followed for analyzing
traffic operations at multilane-large-diameter not-conventional roundabouts. The research follows a
theoretic-experimental approach that intends to put in a fair equilibrium the need both to match field
observations and to have a general criterion to determine behavioral parameters, on which traffic
performances depend.
The main idea of the proposed approach derives from field observations at not-conventional roundabouts
which show traffic operations following a pattern of a consensus of right-of-way alternating between
vehicles entering from the approach and those streaming in the circulating lanes. A generalized model,
similar to that one characterizing All-Way-Stop-Controlled (AWSC) intersections, was implemented,
accounting for peculiarities revealed by an in-depth exploratory analysis of field data at not-conventional
roundabouts.
As basic behavioral parameters (e.g. saturations headways) elude direct observations, i.e. operational
conditions in which they are observable rarely occur, in this paper a procedure to draw them from
macroscopic observations of traffic conditions has been proposed. For this purpose, a regression analysis
was carried out starting from observational data; the presence of response correlation required the
regression parameters to be estimated through Generalized Estimating Equations models (GEEs), i.e.
developing a marginal model for the unobservable - unknown - parameters