Article
citation information:
Duda, K., Sierpiński, G. Traffic organisation
problems at non-signalised intersections – case studies of visibility
distance and ‘give way’ and ‘stop’ road signs. Scientific Journal of Silesian University of
Technology. Series Transport. 2019, 102,
41-52. ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2019.102.3.
Kamil DUDA[1], Grzegorz
SIERPIŃSKI[2]
TRAFFIC
ORGANISATION PROBLEMS AT NON-SIGNALISED INTERSECTIONS – CASE STUDIES OF
VISIBILITY DISTANCE AND ‘GIVE WAY’ AND ‘STOP’ ROAD
SIGNS
Summary. The paper analyses traffic organisation at
non-signalised intersections. In such locations, the use of correct road signs
is crucial. Traffic engineers should consider a balance between traffic fluency
and safety. Sometimes, limited visibility necessitates the use of a
‘stop’ sign. The paper includes case studies for selected
intersections in the Silesia Province, Poland.
Keywords: visibility distance,
‘give way’ and ‘stop’ road signs, road safety
1. INTRODUCTION
Every day on our roads, we may
observe intensive road traffic generated by commuters especially in large
cities and urban agglomerations. [1, 10]. Traffic control is unavoidable if we
are to prevent accidents and reduce the number of injured people and fatalities
[3]. Additionally, road incidents translate into the cost of emergency service
interventions, delays at work, the cost incurred by drivers due to congestion,
and cost related to mental health disorders. Relevant traffic control enables
road users to avoid incidents and facilitates the efficient flow of vehicles at
intersections, particularly in core city centres.
Regarding road safety, the lack of
appropriate signage is a serious problem. In many instances in Poland, the
development of road signage falls behind the increase in traffic [1]. Moreover,
drivers frequently ignore road signs, which leads to road incidents making
travelling burdensome. Since every location in the road network has different
parameters, it is necessary to adjust safety measures to the actual traffic
[11-13, 16]. Although, road incidents most often happen due to human error, the
surrounding or adverse traffic conditions impacts on drivers’ judgements
[8]. Therefore, it is important to provide relevant roads signs that are
straight-forward and not misleading for drivers and do not pose a threat to
road traffic safety, and consequently, do not stimulate decisions that may
compromise safety and contribute to road accidents [2]. Not only does the
appropriate signage help to avoid dangerous situations on our roads, but it
also reduces the cost of dealing with the aftermath of accidents. In Poland,
rules pertaining to road signs and traffic management are defined in relevant
laws, including [5, 6, 8].
2. ROAD SIGNS AND VISIBILITY
DISTANCE AT NON-SIGNALISED INTERSECTIONS
The road traffic
organisation is based on a set of rules for vehicles and pedestrians to
observe. The traffic organisation is one of the major responsibilities of a
traffic management body. The goal is to ensure traffic fluency and guarantee
safety in a given area of the road network. An indispensable component of the
traffic organisation is road signage, both vertical and horizontal, and traffic
lights [9, 14].
Traffic organisation is
particularly important in locations with likely potential collisions involving
traffic participants. It is possible to reduce the number of prospective
collisions by applying relevant traffic measures. This, however, is not always
possible. An intersection, where roads cross or connect, is usually a place of
the largest number of accidents [4].
Visibility at
intersections can be defined using such parameters as the visibility area,
referred to as the visibility triangle, and the stopping visibility distance.
The latter is the minimum distance for the driver to see a road sign, warning
or danger and react early enough to avoid a road incident. The visibility area
is defined depending on the permitted speed at a given road, curve radius and
building facilities situated along the road. The ‘Regulation of the
Minister of Transport and Maritime Economy of 2nd March 1999
concerning technical conditions to be met by public roads and their
locations’ [5] provides minimum values of the visibility distance for
various road types. Below, Figure 1 presents the visibility area for a car
approaching an intersection and minimum sight distances [5, 9, 15]. Figure 2
shows the visibility area for a vehicle moving from the place it stopped and
minimum sight distance values [5]. An important aspect of traffic organisation
is that signage needs to be adjusted to in accordance with the features of its
surrounding.
Fig. 1. Visibility area while
approaching an intersection based on [5]
Fig. 2. Visibility area while
moving from stop location based on [5]
At intersections without
traffic lights, either A-7 or B-20 sign is set at the connecting road. In the
case of the A-7 ‘Give Way’ sign, vehicles stop when a car is
approaching along the road with right of way, whereas in the case of the B-20
‘Stop’, vehicles are obligated to stop, which automatically
increases their safety before they merge with the traffic. The B-20
‘Stop’ sign is more restrictive for drivers than A-7 ‘Give
Way’. From the viewpoint of traffic fluency, the less restrictive solution
(A-7) is more justified. However, in a number of instances, especially in the
case of poor visibility, that sign should be replaced with the B-20 sign which
is more unambiguous in defining driver’s behaviour.
3. CASE STUDY
For the purpose of the study, the analysis covered
four locations with major visibility issues at their intersections with the
right of way roads. Each of those locations was thoroughly examined at the site
with driver’s behaviour observed as well. The locations were also
analysed for road incidents and frequency while taking into consideration the
traffic volume. Finally, changes in the traffic organisation were proposed to
improve safety. The analyses covered the following locations:
#1 intersection
of Opatowicka and Opolska streets in Tarnowskie Góry.
#2 intersection
of Pukowca and Bocheńskiego streets in Katowice.
#3 intersection
of Łagiewnicka, Krzyżowa and Świętochłowicka streets
in Bytom.
#4 intersection
of 9 Maja and Karola Miarki streets in Chorzów.
3.1. Current situation
At each intersection, the Give Way sign
(A-7) was set at the connecting street. The analysis of the actual situation
revealed visibility issues at each intersection. At some intersections, other
problems were noted as well.
Case #1
The intersection is situated in Tarnowskie Góry
and shortens the travelling distance for drivers using the ring road and for
the inhabitants when travelling to the city centre. The A-7 sign was set at
Opatowicka Street. Due to a very small angle between Opatowicka and Opolska
streets (ca. 20°) and poor stopping visibility distance, the
sign should be replaced by the ‘Stop’ sign (B-20) according to
principles defined in the Regulation on technical conditions for public roads
and their locations. The situation is presented in Figure 3. The observation
showed that drivers approaching the intersection from Opatowicka Street,
desiring to turn right needed to rotate their heads significantly to make sure
that they give way to vehicles moving along Opolska Street. While doing so,
they were not able to pay attention to the immediate surrounding in front of
their cars, which frequently required them to brake abruptly to avoid collision
with a preceding vehicle if it moved at a smaller speed. The intersection with
Opatowicka Street lacks horizontal signs indicating the right of way.
Fig. 3. Traffic
organisation and stopping visibility distance at the intersection with
Opatowicka Street (case #1)
Case #2
The intersection is situated in the north-west part of
Katowice. It plays the role of the connecting point. Bocheńskiego Street
is one of the major streets in the city connecting with the A4 motorway
situated 1 km away from the intersection. The street enables for fast
travelling to the city centre. Although at the merging point with
Bocheńskiego Street a ‘Give Way’ (A-7) sign has been placed,
the arrangement of Pukowca Street and Bocheńskiego Street causes the
situation of reduced visibility. Another issue is the lack of a merging lane
along Bocheńskiego Street (for vehicles driving along connecting roads),
which combined with the shortage of horizontal signage may be misleading for
drivers. This has been confirmed by the observation of drivers at the superior
connecting road. They had to brake suddenly when someone failed to give them
right of way and also drivers moving along Pukowca Street had to brake at the
very last moment before merging with the main traffic. Traffic organisation and
visibility field at Pukowca Street are presented in figure 4.
Fig. 4. Traffic
organisation and stopping visibility distance at Pukowca Street (case #2)
Case #3
The intersection without traffic lights is situated in
the southern part of Bytom. The street with the right of way connects the
Łagiewniki District with the city centre. Increased traffic at the
intersection can be seen mainly during the morning and midday peak hours.
Numerous trees and bushes growing along the road disrupt visibility for drivers
moving along the subordinate road which has the A-7 sign set close to the
intersection. Drivers merging with the traffic from Krzyżowa Street find
it difficult to see other vehicles on the right of way street. It is
particularly dangerous in the case of drivers turning left when cars at the
subordinate connecting point must give way to cars moving along each of three
lanes. The traffic organisation and stopping visibility distance at the
intersection are presented in Figure 5. The observation revealed two types of
hazardous behaviour among drivers coming from the subordinate connecting road
and turning left. On one hand, drivers turning left at Krzyżowa Street
often merge with the traffic after they are sure of no incoming vehicle along
Świętochłowicka Street, but at the same time, they ignore cars
on the connecting Łagiewnicka Street. While on the other hand, drivers
approaching the intersection without reducing their speed, had to brake sharply
to avoid collision with cars coming along the right of way road when they
noticed it at the very last moment.
Fig. 5. Traffic organisation at the
intersection and stopping visibility distance at connecting Krzyżowa
Street (case #3)
Case #4
The final case study involves an intersection without
traffic lights in the centre of Chorzów. The intersection connects 3
Maja Street, which is one of main east-west city highways, and Karola Miarki
Street, which is a major road connecting the northern districts of
Chorzów with the city centre. Moreover, 3 Maja Street also conveys the
tramway traffic. The intersection is situated in the dense build-up residential
area. Traffic from the subordinated connecting road is controlled by the A-7
sign. However, the dense residential development significantly reduces
visibility for drivers coming from the subordinated connecting road and turning
right as well as those turning left. Visibility is further limited by cars
parked along 3 Maja Street, in the immediate vicinity of the intersection.
Traffic organisation and stopping distance visibility at the intersection are
presented in Figure 6. The observation showed that drivers coming along the
subordinated connecting road, find it difficult to see cars approaching along
the right of way street. This frequently leads to failure to give way. The
situation is particularly dangerous for cars turning left since they need to
give way to vehicles moving along the 2 lanes and the tram as well.
Fig. 6. Traffic organisation at the
intersection and stopping visibility distance at T-junction with Karola Miarki
Street (case #4)
3.2. Causes of road incidents
The analysis covered data for selected
intersection concerning the number of road incidents. Data originated from
relevant police records and the SEWiK system (Accident and Collision Register).
Table 1 includes 2016 and 2017 data with a breakdown of causes of incidents. As
observed, the main causes include the failure to give way and failure to keep a
safe distance between vehicles. In the last case (#4), inappropriate turning
was a major cause.
Tab.
1
Road incidents in 2016 and
2017 at intersections examined.
|
|
#1 |
#2 |
#3 |
#4 |
||||
|
Cause |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
2016 |
2017 |
|
Failure to give right of way |
|
|
4 |
3 |
4 |
3 |
1 |
1 |
|
Failure to keep safe distance |
2 |
3 |
4 |
2 |
1 |
|
2 |
1 |
|
Inappropriate turning |
|
|
1 |
|
|
|
1 |
3 |
|
Inappropriate passing |
|
1 |
|
1 |
|
|
|
|
|
Inappropriate reversing |
|
|
|
2 |
|
|
|
|
|
Inappropriate overtaking |
1 |
|
|
|
|
|
|
|
|
Failure to observe road signs and other signals |
|
|
1 |
|
|
|
|
|
|
Inappropriate change of lane |
|
|
1 |
|
|
|
|
|
|
Poor health |
|
|
|
|
|
1 |
|
|
|
Driving into road hole |
|
|
|
|
|
1 |
|
|
|
Failure to give way to pedestrians |
|
|
|
|
|
|
1 |
|
|
Unknown |
1 |
|
|
|
|
|
|
|
|
TOTAL |
4 |
4 |
11 |
8 |
5 |
5 |
5 |
5 |
It should be noted that
the main causes of incidents might be related to poor visibility when merging
with the traffic from a road with right of way. Due to poor visibility, drivers
fail to give way or need to brake abruptly or brake too late and risk a
collision with a preceding car on the road.
3.3. Proposed improvements
The analysis of the actual situation,
information about incidents, and observations on those intersections helped in
developing proposals for improvements. In each of the cases, it was suggested
that the A-7 sign should be replaced with the B-20 sign to deliberately force
drivers to stop at the connecting road. This may cause loss of time at the
intersection during off-peak hours (when traffic volume is reduced on roads
with the right of way). However, in the opinion of the authors, the change can
improve safety at intersections. The changes for particular cases are described
below.
Case #1 – Proposed changes
A suggested solution that would improve traffic
safety involves replacing the A-7 sign with the B-20 sign. Moreover, the
intersection design should ensure that the angle between streets is close to
90° with a 20° tolerance. This improves visibility for drivers
approaching the intersection and it gives them the opportunity to react faster
in case of danger [9]. For the reason, of solving the problem of the small
angle between Opolska and Opatowicka streets, and improve the visibility area
as well, it is suggested that the connection with Opatowicka Street be rebuilt
and the angle with Opolska Street reconstructed closer to a 90° orientation
(Figure 7).
Fig. 7. Proposed
rebuilding of intersection of Opolska and Opatowicka streets (case #1)
Case #2 – Proposed changes
It is advised that the vertical sign A-7 ‘Give
Way’ be changed to the B-20 ‘Stop’ sign. Additionally,
horizontal signs should be placed for the B-20 sign to clearly set the stop
point for a car before entering the possible conflict zone with cars enjoying
the right of way (Figure 8). Application of the suggestion can stop
misunderstanding between drivers as they would be sure to give way and approach
merging lane without confusion. These suggested changes do not necessitate the
rebuilding of the road infrastructure.
Fig. 8. Suggested
traffic organisation at the connection with Pukowca Street (case #2)
Case #3 – Proposed changes
It is suggested that road signs be changed
(Figure 9). Again the proposal is to replace the A-7 sign with the B-20 sign to
force drivers to stop and give way if necessary. This should help drivers to
cross the intersection safely. The solutions suggested, requires drivers to
stop before entering the intersection, however, principally the proposed
changes in road signs increase the stopping visibility distance.
Fig. 9. Suggested traffic
organisation at the connection with Krzyżowa Street (case #3)
Case #4 – Proposed changes
In this particular case, we suggest replacing the
vertical A-7 ‘Give Way’ sign with the B-20 ‘Stop’ sign
and reducing the number of parking places as well as fitting posts that prevent
drivers from parking close to the intersection (Figure 10). The change
partially improves visibility at the connecting road and at the same time
enhances the certainty that the right of way is respected by drivers moving
along roads without right of way.
Fig. 10. Suggested traffic
organisation at the intersection of 3 Maja and Karola Miarki streets (case #4)
4. CONCLUSION
Traffic organisation is one of the basic
elements of transport infrastructure which is decisive regarding safety at
intersections. Due to different configurations of the surrounding, every
intersection requires an individual approach as regards organisational
measures. In the case of a non-signalised intersection, proper visibility is
particularly important, since at the access road without right of way a driver
makes an individual decision to go through the intersection (no traffic
lights). The use of a Stop sign, as proposed in the article, forces drivers to
stop at the connecting point. On one hand, a drawback of the solution is time
lost at the connection point, since the car needs to stop there. On the other
hand, the solution provides clear information to the driver to give way and
necessitates the driver to examine the actual traffic on the right of way
street.
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Received 17.10.2018; accepted in revised form 20.12.2018
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