SAFE DESIGN OF RURAL ROADS BY NORMALIZED ROAD
CHARACTERISTICS
Thomas Richter, Prof. Dr.-Ing.
Technische Universität Berlin, Department road planning and operation
Benedikt Zierke, Dipl.-Ing.
Technische Universität Berlin, Department road planning and operation
ABSTRACT
The standard designs of rural roads vary a lot and show several failings
affecting the road safety negatively. The paper presents some results of a
categorization of existing roads. This standardization of road design is
believed to identify low volume roads and therefore harmonize the driving
behaviour and increase the road safety. Based on empiric analysis road
sections were dedicated and evaluated. The new single lane cross section for
low volume roads showed positive results. Overall, the results of the project
indicate that normalised road characteristics within design classes have
positive effects on the driving behaviour and therefore the safety level on
roads.
1
INTRODUCTION
Within the project "safe design of rural roads by normalised road
characteristics" (Richter & Zierke 2008) the TU Berlin was researching which
road designs affect driving behaviour and road safety positively. The project
aims are to provide self-explaining and recognizable roads and therefore
increase road safety by creating design classes. Based on detailed accident
analyses the design classes were derived. Besides the cross-sections
including their road markings, the junction design and operation and the
alignment were considered within the deliberations of safe design classes.
The driving behaviour was examined in with/without and before/after
situations on real roads. The empiric analyses on the test tracks were
conducted by means of stationary radar measurements and the following-car
technique on 30 different roads (over 10.000 km). Furthermore the detected
self-explaining roads were analysed in the driving simulator of the TU Berlin.
To ascertain the effect of these new kinds of roads they were compared with
real roads implemented into the driving simulator. Besides driving speed,
acceleration and lane keeping were measured along the stretch of road and
locally on the real road as well as in the driving simulator.
Current situation
The standard designs of rural roads vary a lot. The question which road
characteristics will lead to safe driving behaviour has yet to be answered. So
far various studies have conducted research on specific road design
elements, but have not been able to give an answer to the questions asked
here. One approach to achieve a high quality road network is the
standardisation of certain road types, which are supposed to have similar road
© Association for European Transport and contributors 2009
1
characteristics within their category, but show significant differences towards
the other road types.
In the course of the development of new guidelines for rural roads, the
“Richtlinien für die Anlage von Landstraßen (RAL) - Guidelines for the design
of rural roads” (FGSV 2008), the aim is to provide self-explaining and
recognizable road types for motorists. According to the new RAL (FGSV
2008) rural roads are being classified by traffic relevance into one of four
design classes. Thus, the designs of the cross-section and junction as well as
the corresponding alignment are playing a decisive role. Expectations are that
the general RAL (FGSV 2008) goals of normalizing rural roads, and through
this positively influencing driver behaviour, will be enhanced by using
characteristic designs.
2
SAMPLE OF TEST TRACKS
The suitable road types were preselected based on the current state of
discussion in task force 2.2.1 of the German Road and Transportation
Research Association (FGSV) „Designing new rural roads“, which classifies
four different categories.
The main demands and goals of the separate road types were defined based
on their role in the network (level of connection). On the one hand they are
supposed to fulfil their regional development function with high road safety
and a reasonable level of service and on the other hand they have to
guarantee a low cost but sustainable protection of the environment and the
surroundings. The consideration of the goals has to depend on the
importance of the rural road for the network. This has to be the case because
the often competing demands that the roads have to meet depend on their
level of connection.
In the target field of road safety the goals of safe horizontal alignment, safe
turning and crossing, safe passing and overtaking and safe roadside could be
deduced from the number and severance of the accidents in a conducted
accident analysis. These goals can be met with a variation of measures. By
using uniform road characteristics in cross-sections, alignment (radii
sequences in particular), type of operation, overtaking concept and
intersection layout the appropriate driving speed should become apparent to
the driver. Considering these results the design classes now contain
characteristic elements in the areas alignment, cross-section design,
intersection design, operation type and roadside furniture. Based on the
network function four design classes consisting of a total of seven road types
were classified.
Design class 1 has to manage the long distance traffic. It consists of a three to
four lane cross section which is designed with a generous alignment to set the
suitable speed to about 110 km/h. The connection of roads is processed by
grade separated junctions. Agricultural traffic and bikes are not permitted.
© Association for European Transport and contributors 2009
2
Figure 1
typical cross sections of design class 1
Design class 2 consists of a two lane cross section with temporarily added
passing lanes (about 15 % for each direction is intended). This 2+1 road still
allows safe passing without using the lane of the oncoming traffic. Passing in
the two lane cross sections is prohibited (see figure 2). The alignment is
supposed to be semi generous to set the suitable speed to about 100 km/h.
The connection of roads is processed by t-junctions with traffic lights. Bikes
are not permitted.
Figure 2
section
typical cross section of design class 2 in the two lane cross
Design class 3 consists of a two lane cross section which displays the regular
rural road. The alignment is supposed to be semi adapted to set the suitable
speed to about 90 km/h. The typical form of junction design is a roundabout.
© Association for European Transport and contributors 2009
3
Figure 3
typical cross section of design class 3
Design class 4 consists of a new approach of cross section design in
Germany. For these low volume roads a new single lane road is believed to
identify these roads and make them distinguishable to others. The suitable
speed is at about 70 km/h.
Figure 4
3
3.1
typical cross section of design class 4
DRIVING BEHAVIOUR ON THE TEST TRACKS
Methodology
Driving behaviour as such cannot be described and must therefore be
determined with the use of indicators. For this purpose three different
parameter categories were used. The vehicle born parameters consist of
parameters along the section and cross-section as well as the parameters on
the driver’s side of the vehicle. The vehicle born data can be split into
longitudinal control (speed, acceleration and deceleration) and the transverse
control (lateral acceleration, lane keeping).
The empirical studies about driving behaviour have been conducted using two
different methods. On the one hand local measurements were taken at certain
locations along the test track. Relevant for the microscopic driving behaviour
was data concerning the speed and lane keeping. On the other hand the
driving behaviour of a single vehicle was monitored with the following-car
technique along the entire test track.
© Association for European Transport and contributors 2009
4
Figure 5
inquiry of the driving behaviour
The analysis of the empirical research was carried out using the aggregated
data from speed, acceleration and lane keeping profiles. Furthermore the raw
data were analysed statistically to verify the reliability of the conclusions or at
least deduce observable trends.
The results of the with/without and before/after study of the design classes
show the positive effects of indicating normalised roads. For each design
class one test track is shown below exemplarily.
3.2
Design class 1
Within design class 1 six test tracks with the characteristic design elements
were analysed. Exemplary one road of about 5.5 km with three grade
separated intersection is shown in figure 6. The profiles show that the driving
speed within the open road and the fly over junctions are quite similar. Larger
speed differences are recognized in between the cross section design. Due to
the amount of lanes, the speed differs on these roads. An example of one test
track is shown in figure 6.
Figure 6
speed profile of a test track of design class 1
© Association for European Transport and contributors 2009
5
3.3
Design class 2
Within design class 2 five test tracks with the characteristic design elements
were analysed. Exemplary one road of about 9 km with two junctions with
signal control is shown in figure 7. The speed profiles of the open road show
that the driven speed is lower than for the test track of design class 1. As seen
in figure 7 the speed limit within the intersections determine the speed within
these sections. To achieve an appropriate speed within the intersections the
length of the area with a speed limit before the intersections should not be
undersized.
Figure 7
3.4
speed profile of a test track of design class 2
Design class 3
Within design class 3 ten test tracks with the cross section design shown in
figure 3 and roundabouts or regular junctions (mainly t-junctions) were
analysed. Figure 4 shows a speed profile of an exemplary road of about 6 km
with two roundabouts. Different to design class 1 and 2 the speed profile
shows a considerably increased harmonization of the speed behaviour which
is displayed by the lower vibration of the velocity. This is basically attributed to
the lack of passing situations. Furthermore the top speeds a much lower.
© Association for European Transport and contributors 2009
6
Figure 8
3.5
speed profile of a test track of design class 3
Design class 4
Within design class 4 seven test tracks with the characteristic design elements
were analysed. One of them was additionally equipped with a new road
marking for a before/after study. After repaving this stretch of road it was the
first test track in Germany on which the new road markings according to the
new RAL (FGSV 2008) were applied. The road markings consist of two
broken edge lines with an offset of 0.75 m from the edges of the road (2 m line
length, S/L = 1/1) according to the RAL (FGSV 2008) (see figure 4). The old
road marking existed of two solid edge lines which could hardly be seen and a
spaced axis line (3 m length, S/L = 1/2).
5,70
2,85
2,85
5,70
4,20
0,75
Figure 9
0,75
Test track before (top) and after (bottom) the remarking
© Association for European Transport and contributors 2009
7
The speed profiles of the before/after study of the test track are shown in
figure 4. The profiles reflect the expected influence of the alignment. An
influence on speed in the area with radii of about 200 m can be noticed.
Interesting is however, that the amount of speed reduction stays the same no
matter which level of driving speed is measured.
Figure 10
Speed profile, speed differences of the test track
The average speed reduction for all percentile speed profiles was about 10
km/h for one direction. The other direction which already had a lower speed
level in the before-situation showed a less noticeable speed reduction. For
both directions though lower entering speeds in the villages could be
ascertained. The local measurements confirm those results. They also show a
reduction in speed for the after-situation by about 10 %.
4
4.1
DRIVING SIMULATOR STUDY
Methodology
As a foundation for the tests in the simulator the existing knowledge about the
composition of suitable road types was utilised. The defined road types were
programmed for the tests in the simulator. They had to be driving behaviour
optimised and include the requested road characteristics. For comparison real
sections, which had been analysed during the empirical research were
integrated into the tests. This allows an evaluation of the driving simulator
comparing the real sections driven in the simulator and in situ on the one hand
and a comparison between the real sections and the driving behaviour
optimised sections on the other hand.
30 test runs per road type were conducted for the study. This means a total of
approximately 6.000 km was driven on the test tracks. In the driving simulator
similar measurements to the ones on the real roads were taken (speed, lane
keeping). Additionally the visual behaviour of the test drivers was captured.
© Association for European Transport and contributors 2009
8
The results of the tests in the driving simulator were statistically analysed in
the same way as the results from the in situ measurements to guarantee
comparability.
4.2
Test sections
In addition to the parameters defined in figure 1 a variation of road markings in
design class 4 was analysed. Furthermore other vehicles with independent
behaviour were added into the simulation in the course of this project. The
traffic situation was hereby initiated location or event related.
Figure 11
roads)
characteristic cross-sections of design class 4 (low volume
The driving optimised road sections were generated based on the suitable
radii calculated. Therefore the circular curves with various radii and the
associated clothoids and angles of aperture were strung together using a
rational relation of radii. The average length of a driving optimised section is 5
kilometres. The sections can be connected indefinitely which allows driving
without discontinuation. Each subject had to drive a total of 20 km on each
test section which allowed identifying random events.
The real test sections were also generated for the simulator comparing the
GPS data from the empirical studies and the existing data from the site plan.
The different cross section design is displayed in figure 6.
4.3
Driving behaviour
The analysis of the average speed behaviour of all test subjects (n=45
rounds) without other traffic resulted in the profiles shown in figure 12. The
average speed in the before-situation was about 95.2 km/h. The after-situation
showed an average speed with a reduction of 5 % to about 91.3 km/h. An
analysis by section for the open road and the junction area shows that the
before-situation showed an average speed of 105.0 km/h and 83.4 km/h. For
the after-situation with the new single-lane cross-section for the open road
section a reduced speed of about 99.9 km/h was noticed. For the junction
area the average speed went up to about 86.3 km/h.
© Association for European Transport and contributors 2009
9
Figure 12
speed profiles of the real driving simulator sections with the old
(before) and the new (after) marking
A precise consideration of the 85 % speed (V85, the speed that 85 % of the
drivers do not exceed) shows, equally to the results on the test track, a
reduced speed in the open road section. Furthermore the speed reduction of
high speed levels decrease stronger than on lower speed levels for the driving
simulator section. The converse progress can be noticed at junctions.
A high homogeneity of the speed profiles increases the safety level. The
homogeneity itself can be displayed by several indicators. One of them is the
frequency of the speed alterations over the road stretch. The total for
alteration in the before situation was higher than in the after situation (46.5 1/h
to 41.5 1/h). Therefore the speed along the stretch was more homogenous in
the after-situation. On the other hand the homogeneity can be displayed by
the variance of the drivers´ speed. Before the remarking the average variance
was 8.2 km/h. The after-situation had a lower average variance of 7.8 km/h.
The 70%-canal of the driving speed (definition of the normal driver) which
displays the difference of the V15 and the V85 (the speed that 15% / 85% of the
drivers did not exceed) did not show clear results.
In contrast to the test sections with the real alignment (generous alignment)
the driving behaviour adjusted alignment (adapted alignment) resulted in
lower driving speeds.
5
CONCLUSION
Overall the speed profiles of the test tracks which are designed with the
characteristic elements of the design classes reflect the suitable speed as
intended. This shows that normalised road characteristics within design
classes have positive effects on the driving behaviour and therefore the safety
level on roads.
© Association for European Transport and contributors 2009
10
In order to achieve the desired driving behaviour, it is not only important that
roads can be distinguished from each other, which can also be enhanced by a
uniform road layout within road types, but also which design elements achieve
this distinction and uniformity.
Therefore road markings are the essential elements to use. Especially on two
lane cross-sections the different design standards were not indicated by the
markings. By creating the new single lane cross-section the low volume roads
are strictly separated from the standard roads.
The implementation of the new design classes will take several years and will
bring along problems in the conversion. Therefore recommendations have to
be given to the planners to ensure the correct effects. Especially transition
zones have to be dealt with cautiously. To ensure these needs the task force
“adjustment of existing rural roads” was established last year. (Richter &
Zierke 2009)
REFERENCES
FGSV (2008) RAL - Richtlinien für die Anlage von Landstraßen (Guidelines for
the design of rural roads), Forschungsgesellschaft für Straßen- und
Verkehrswesen, Köln, Entwurf (blueprint)
Richter, Th., Zierke, B. (2008) Sichere Gestaltung von Landstraßen durch
normierte Streckencharakteristik (Safe design of rural roads by normalised
road
characteristics),
DFG-Zwischenbericht,
Berlin,
unveröffentlicht
(unpublished)
Richter, Th., Zierke, B. (2009) Ergänzungen der Richtlinien für die Anlage von
Landstraßen (RAL) zur Anwendung beim am Bestand orientierten Um- und
Ausbau (FE 02.293/2007/FRB) (Amendments of the RAL for the adjustment of
existing rural roads), BASt-Zwischenbericht, Berlin, unveröffentlicht
(unpublished)
REFERENCES
Since 2003 Thomas Richter is professor and head of the
department road planning and operation at the Technische
Universität Berlin. Since 2000 Prof. Richter is CIO of SHPIngenieure in Hannover. From 1993 to 2000 he was project
manager of the SHP-Ingenieure for over 200 projects for
traffic surveys, feasibility studies and the design of road
infrastructure as well as further research projects in all
fields. In between 1990 and 1993 Prof. Richter was after
graduating from the University of Hannover research
assistant at the University of Hannover. His research
emphases were the design and the operation of junctions. Thomas Richter is
a member of several task forces of the German Road and Transportation
Research Association (FGSV) for new guidelines in Germany.
© Association for European Transport and contributors 2009
11
Benedikt Zierke is scientific assistant at the department
since 2006. Before he started his doctor (phd.) thesis on
safe design of rural roads he was working during his
course of study at the University of Hannover for the SHPIngenieure. His research activities at the Technische
Universität Berlin contain the safe design of road
infrastructure and traffic flow analysis. Benedikt is also part
of the task force “adjusting existing rural roads” of the
German Road and Transportation Research Association
(FGSV).
Technische Universität Berlin
TIB 3 / 3-3, Gustav-Meyer-Allee 25
13355 Berlin, Germany
[email protected],
[email protected]
Phone: + 49 (0) 30 314 72 553
Fax: + 49 (0) 30 314 72 884
© Association for European Transport and contributors 2009
12