Microsimulation Applied to Roundabout Performance Analysis: the Effect of Pedestrian Crossings
A M C Bastos Silva, Universidade de Coimbra, PT ; L Vasconcelos, Instituto Politécnico de Viseu, PT
This paper presents a study on the influence of pedestrian crossings on roundabout performance, using microsimulation. The effect of a crosswalk in various points of the exit with different levels of vehicle and pedestrian demand is evaluated.
The good performance levels of roundabouts have justified, all over the world, the development of countless research studies and design support manuals with most of them including performance levels estimation models. However it is unusual to find references of research work focused on the influence of pedestrian crossings in the corresponding performance level of the roundabout although it is recognized that roundabouts are mainly used in urban areas and therefore the pedestrian presence can be quite significant. Until the latter 90?s, the capacity estimates were simple analytical estimates, ignoring pedestrian influence. The ?Roundabouts an Informational Guide? developed by Federal Highway Administration (FHWA) is one of the first references that allows the correction of entry capacities, taking in account the pedestrian impedance effects.
However, the more significant works were motivated by the increased relevance of safety issues, under the National Cooperative Highway Research Program Project NCHRP 3-78a. These works were directed for the development of measures that can provide safe crossing conditions for disabled persons, with a special concern about blinds. The first results are promising, though extremely limited to the North American legal structure. In fact and contrarily to what happens in most European countries the crosswalk sign W11-2 doesn?t give the pedestrian absolute priority and therefore he has to evaluate his crossing opportunities.
Regarding the European research, most of the works are analytical-based, requiring a great set of assumptions to be applicable to real-world problems. More practical approaches where tried using microscopic simulation, although also relying in simplistic assumptions (e.g. vehicle and pedestrians constant speed).
It can be concluded that the existing research reflects a diversity of approaches and remains inconclusive. Many measures should be further studied, namely the traditional zebra crossing (study of optimal locations), the controlled crossings (pelican, puffin, toucan) and new solutions adapted to the disabled users.
Therefore this paper presents the some results of an exploratory study on the influence of pedestrian crossings on roundabout performance. The work is developed with the Paramics microscopic model after calibrated to the local conditions in accordance to observed data. In this phase it was opted to focus the study in a normal roundabout characterized by two entry and circulatory lanes since this solution is the most usual in structural roads where the vehicle is more important than the pedestrian.
Using microsimulation the effect of using a crosswalk in various exit locations subject to several levels of pedestrian and traffic demand on the roundabout performance is evaluated. The potential and main application domain of light controlled crosswalks comparatively to normal solutions is also evaluated. At this level and based in several crossing strategies the effects of pedestrians of mobility impaired pedestrians will also be assessed.
Finally the results obtained are validated by direct observations in a normal roundabout that has a light controlled pedestrian crossing with one phase timing. Those results can allow the evaluation of the benefits associated with the development of other traffic light control solutions/strategies and therefore optimize the global functioning of the system.
In this paper the investigation base assumptions are presented as well as the adopted performance indicators and the main results. Future developments are also discussed.
Association for European Transport