Table Of ContentWerner Brilon (Editor)
Intersections without
Traffic Signals II
Proceedings of an International Workshop
18-19 July, 1991 in Bochum, Germany
With 163 Figures
Springer-Verlag
Berlin Heidelberg NewY ork
London Paris Tokyo
Hong Kong Barcelona Budapest
Prof. Dr.-lng. Werner Brilon
Lehrstuhl fUr Verkehrswesen
Ruhr-Universitat Bochum
UniversitatsstraBe 150
4630 Bochum
This workshop was made possible by the generous support of the
following organisations:
Deutsche Forschungsgemeinschaft (German Council for Research)
Minister fUr Stadtentwicklung und Verkehr
des Landes Nordrhein-Westfalen
ISBN -13: 978-3-642-84539-0 e-ISBN -13: 978-3-642-84537-6
DOl: 10.1007/978-3-642-84537-6
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Preface
In March 1988, an international workshop on intersections without traffic signals was
held at the Ruhr-University in Bochum, Germany. The proceedings of this workshop
were published by Springer 1). The workshop was performed in a very harmonious
atmosphere, which stimulated the experts from different countries to communicate and
exchange their ideas and experiences. The presentations and the written contributions
documented the present state of technical solutions for design and engineering of unsi
gnalized intersections both regarding scientific research and practical applications.
Moreover, numerous unsolved problems were identified.
Thus, the 1988 workshop stimulated new developments in the field of unsignalized inter
sections in several countries. In the meantime, these investigations have lead to a
remarkable progress. For example in Germany a new guideline for unsignalized cross
intersections and T-junctions has been finished and is going to be introduced in 1991.
New results on roundabout capacity have been worked out as well. Many particularly
important developments were made in foreign countries. Especially in the United
States, an increasing interest in this subject can be observed. In the annual meetings of
the TRB, this item received great attention. Many research institutes in North America
have concentrated their activities on that point. A new TRB-circular concerning
unsignalized intersections is going to be published. It will contain a new procedure for
four-way-stop-control intersections, which seems to be a special feature of North
American traffic engineering. However, new results from the US for two-way-stop
control intersections are available as well.
Especially in the field of roundabouts - or "rotaries", which seems to be the American
term -some progress has been made. Roundabouts are on the advance worldwide. Many
countries like Australia, France, Norway, Sweden, Switzerland and Germany are in
creasingly using roundabouts as an intersection design which bears comparison with
other solutions or which is even more advantageous. This increasing use of roundabouts
induces a great variety of new experiences both in the field of intersection capacity and
with intersection design and traffic safety.
1) W. Brilon (editor): Intersections Without Traffic Signals.
Springer Verlag, 1988, ISBN 3-540-18890-8.
VI
The progress made between 1988 and today supported the idea of holding a second
international workshop on unsignalized intersections. This was also confirmed in discus
sions with experts from different countries. The Ruhr-University Bochum will again host
this event. The fact that a second workshop is held on the same item at the same place,
however, should not establish this event as another continuous series of traffic enginee
ring congresses.
The general situation in the theory of capacity for unsignalized intersections is still cha
racterized by the discussion between gap-acceptance theory and empirical regression
models. Both still have their own specific advantages and drawbacks. Therefore, both
approaches are in use in different countries. It can be stated that the more theoretically
based gap-acceptance theory is still applied for cross-intersections and T-junctions in
many countries. As many of the contributions to the workshop point out, this theory is
still capable of further improvement. One reason for the use of this fundamental theory
may be that it provides a better understanding of individual operations and of the hier
archy of traffic streams at such intersections. Thus, it enables an extrapolation of solu
tions for traffic flows which have not been observed in reality. The regression theory,
however, is also more and more observed with interest outside Great Britain, which has
the longest experience with this general approach. Presumably -with few exceptions- it
has occupied nearly the whole field of roundabout capacity calculations. The reason for
this could be that this approach is more suitable for handling driver behaviour which dif
fers from pure gap-acceptance patterns like gap-forcing and priority reversal. The idea
that critical gaps and move-up times could depend on the traffic load of the intersection
could become an approach to overcome these differences.
To detect these kinds of effects, the precise evaluation of critical gaps from traffic obser
vations could again become a field requiring increasing attention in the future.
This point of discussion brings us back to the basic fact that modelling in traffic enginee
ring always contains two aspects: the mathematical construction and solution of the
model on one side and the implementation of driver behaviour on the other side. For
further improvements of traffic engineering methods, especially the aspects of a more
sensitive and realistic modelling of driver behaviour by the models as well as by the
parameters being included into the models will become increasingly important.
Moreover, some of the differences between the approaches and the experiences from
various countries could be due to basic differences in behaviour of road users.
Beyond intersection capacity estimations, however, the improved safety of traffic opera
tions on our roads is the most essential task for traffic engineers. This is especially true
for the decisions on control strategies and on types of intersection design. The contribu-
VII
tions to the workshop consider this aspect as well. Unfortunately, due to the closely
packed timetable, only one contribution which concentrates on safety could be included,
although two more interesting papers on this issue had been proposed. However, almost
every contribution pays special attention to the aspect of traffic operation safety, which
is an argument for more integrated considerations of design, capacity and traffic safety.
For the preparation of the workshop, a number of papers from several countries have
been invited to give a current overview of the whole subject considering the respective
circumstances of the specific countries. In addition, a call for papers was sent out in Sep
tember 1990, resulting in an interesting variety of abstracts proposed for the workshop.
From these, a series of 15 papers has been selected by the advisory board (Prof. Keller,
Munich; Prof. Retzko, Darmstadt and Prof. Brilon, Bochum). The work of this group
and especially the excellent discipline of the authors regarding the quite narrow sche
dule for the preparation of the manuscripts should particularly be commended, since it
enables the presentation of the proceedings just in time for the workshop.
The authors and the editor hope that this publication and the workshop itself will con
tribute to continued efforts within the community of traffic engineering researchers and
practicians. Moreover, this event should accelerate the international exchange of new
ideas and generate new impulses for further developments on this specific item of un
signalized intersections as one part of the whole field of traffic engineering.
Bochurn, April 1991 Prof. Dr.-Ing. W. Brilon
Contents
Capacity and Safety of Roundabouts in Germany
Stuwe. B ......................................................................................................... 1
Polish Guidelines for Capacity Analysis of
Priority Intersections
Tracz, M ...................................................................................................... 13
Aspects of the Calculation of Unsignalized Intersections
Schnabel, W. ............................................................................................... 27
Roundabouts in Switzerland -Recent Experiences,
Capacity, Swiss Roundabout Guide
Simon, M ..................................................................................................... 41
Experiences with Intersections without Traffic Signals
in Great Britain
Peirce, J ....................................................................................................... 53
Calculation Procedures for German Practice:
Intersections without Traffic Signals
Brilon, W./Grossmann, M ....................................................................... 62
Modular System for Traffic Simulation at Intersections
and in Networks
Friedrich, B./Ploss, G ............................................................................... 83
A Comparative Study of Roundabout Capacity Procedures
Hakkert, A.S./Mahalel, D./A sante, SA. .............................................. 93
Roundabouts and Road Safety
Alphand, F./Noelle, U./Guichet, B. .................................................... 107
Evolution of Design Rilles for Urban Roundabouts in France
Alphand, F./Noelle, U./Guichet, B. .................................................... 126
IX
Case Study. Performance Effects of Changing a
Traffic Signal Intersection to Roundabout
Hoglund, P ................................................................................................ 141
A Microscopic Simulation Model of Roundabout
Entry Operations
Tan, Jian-an .............................................................................................. 159
A General Capacity Formula for Unsignalized
Intersections
Wegmann, H ............................................................................................. 177
Intersections without Traffic Signals -Swedish
Experiences on Capacity and Safety
Bergh, T ..................................................................................................... 192
A Strategy to Optimise the Geometric Design of
Isolated Priority Junctions
Borzym. I./Silcock, J.P. ........................................................................... 214
Hungarian Measurin~ Results: Observations and
Methods for Calculating Capacity at Intersections
without Traffic Signals
Benyei, A./Fi, I. ....... :. .............................................................................. 226
Unsignalized Intersections and Roundabouts in
Australia: Recent Developments
Troutbeck, R ............................................................................................ 238
Gap Acceptance and Risk Analysis at Unsignalized
Intersections
Lassarre, S./Lejeune, P .......................................................................... 258
Use, Design and Safety of Small Roundabouts
in Norway
Seim, K ..................................................................................................... 270
x
Accident Prediction Models for Unsignalized and
Signalized Intersections
Huang, Y./May, A .................................................................................. 282
Gap Acceptance, Wait Time, and Risk Aversion at
Unsignalized Intersections
Fricker, 1./Gutierrez, M./Moffett, D .................................................. .297
Simulation of Multilane Stop-Controlled T-Intersections
by KNOSIMO in Canada
Chan, P./Teply, S. ................................................................................... .308
Estimating High and Low Flow Rates at Unsignalized
Intersections
Virkler, M./Madsen, R./Sutton, 1. ...................................................... .320
Empirical Models for Estimating Capacity and Delay at
Stop-Controlled Intersections
Kyte, M./Zegeer, 1./Lall, B ................................................................... 335
Capacity and Safety of Roundabouts - German Results
Birgit Stuwe
Lehrstuhl flir Verkehrswesen, Ruhr-University, Bochum, Germany
SUMMARY
The objective of the research project described in this paper was to develop a formula
for calculating the capacity of roundabouts. These formulae were developed by use of an
empirical procedure and regression techniques. Therefore, traffic flow at several
roundabouts was observed and recorded by video equipment. Based on the assumption
that the entry flow was saturated, traffic flow of entering and cirulating vehicles were
analysed and counted in 1-minute intervals. Based on this data samples, a provisorial
formula has been developed for the prediction of roundabout capaClty. Four different
curves have been specified according to dependance upon the number of lanes in the
circular and the entry. These curves are used in practice for capacity calculations of
roundabouts in Germany.
Furthermore, an investigation of accident data is described in this paper. In particular
the accident research confirmed considerable increase in traffic safety at roundabouts
compared to signalised or unsignalised intersections. Accident severity is reduced at
roundabouts. It was found that the roundabout is a good solution to increase traffic
safety.
INTRODUCTION
Places and sites of circular shape have been an instrument of city and town planning
since the Middle ages and especially during the Renaissance. Circular places were suited
where it was worth to emphasize the significance of a place. It was an idea of Henard to
implement one-way traffic on such greater places and thus the Place de l'Etoile in Paris
was the first roundabout.
Also in Germany roundabouts have been constructed especially during the 30ies and
50ies. Later on, many of the existing roundabouts in Germany were rebuilt into junctions
with traffic signals. Roundabouts were not paid attention to any more -especially due to
a lack of suitable capacity estimations, of bad accident experience and also because of a
misinterpretation of the existing rules. Traffic engineers assumed that they would have
to treat the entries like waving areas. The length of the waving area determines the
capacity of such facilities. So the capacity increases with the length, which means that
