First International Conference for PhD studen ts in Civil Engineering [608635]

First International Conference for PhD studen ts in Civil Engineering
CE-PhD 2012, 4 -7 November 2012,Cluj -Napoca, Romania
www.sens -group.ro/ce2012

Road Plantations and Optical Comfort

Filomela Săvoiu*1, Ștefan Horon2

1,2 eng. Drumex Cluj Napoca, PhD Students , Technical University of Cluj -Napoca, Faculty of Civil
Engineering. 15 C Daicoviciu Str. , 400020, Cluj -Napoca, Romania

Abstract

Critical situations that appear along the way (crests, curves without visibility, junctions), the
insufficient signalization on roads, are common causes of accidents. Traffic at night, fog or rain,
are aggravating factors in terms of road safety. In this context, road plantations can help the driver
to focus better, so that his reactions to road conditions become improved. This paper addresses
some critical situations in terms of driver’s perception and ways to solve these situations by road
plantations.
Keywords: optical comfort, critical points, road plantations , roundabout, crest

1. Introduction

The World Health Organization estimates that about 1 million people die each year on roads around
the world, 50 million are injured, causing damage of 578 billion dol lars. Without intervention, it is
estimated that the number of deaths due to car accidents will reach about 2.3 million in 2020. In
Romania, the situation is one of the worst in Europe. In 2008 there were 142 deaths / 1 million
people.
Regarding distributi on by place where the accident occurred, the largest increase in the number of
accidents on unincorporated area roads in 1999 -2008 was recorded in Romania (210%), reaching 53
deaths / 1 million people. [6]
The interaction between driver -road routes is impo rtant in a large percentage of road accidents.
Traffic is subjected to the action of a multitude of variables that are difficult to manage. The most
important factor, which is also the most difficult to control, is the human factor. [3]
In one study, the D epartment of Education and Training in New South Wales Australia found that:
 The human factor is the cause in 67% of accidents ;
 The vehicle is the cause in 4% of accidents ;
 Elements of the road are due in 4% of accidents.
In reality, these factors combine. Under these conditions, road elements already have a higher
contribution, of 28%, combined with human and vehicle factors, as shown in Figure 1.

* Corresponding author: Tel./ Fax.:[anonimizat]
E-mail address: [anonimizat]

First International Conference for PhD studen ts in Civil Engineering
CE-PhD 2012, 4 -7 November 2012,Cluj -Napoca, Romania
www.sens -group.ro/ce2012

Figure 1 – Percentage of factors involved in accidents

Optical comfort is the characteristic of a road w hich is resulting from the superposition of all the
geometric elements of horizontal alignment , vertical alignment and cross section s. It defines the
quality of a road on referring to the perception, from a sufficient distance of the platform and the
confi guration of the route to be traveled, as well as framing the surrounding landscape. [4]
Road plantations are carried out in areas bordering roads in order to reach a set of functions:
technical (slope protection, water sanitation, etc.), road (road benchma rking, comfort and leisure,
etc.), ecological (favorable microclimate, pollutants filter, etc.) and landscape (aesthetic
improvements of the area, masking unpleasant aspects etc.) [5]
Road function has a special role in traffic safety as plantations must m ark the road and provide the
accentuation of the route, increasing visual comfort.
By their shape, composition and role, the main categories of plantations carried along the route are
as follows:
o Row plantations – both trees and shrubs
o Plantations with i solated trees and shrubs
o Group plantations
o Plantations in rows alternating with groups
o Band plantations
o Plantations for strengthening embankments
o Hedge plantations
o Grassings
Also, with an appropriate setting, usually in bands, on more rows with different h eights, road
plantations may be protection curtains against heavy snow falls and strong winds .
Accordin g to the “ Instruction regarding the road plantations ”, developed by National Road
Administration , the trees and shrubs size is classified in table 1:

Table 1 : Clasification of trees and shrubs
Size I II III
Trees >25 m 15 – 25 m 7 – 15 m
Shrub 3 – 10 m 1 – 3 m <1 m

The species usually used are selected under the following criteria: adaptation to climate and soil,
resistance to wind, drought and pol lution, root system, inexpensive maintenance etc.

First International Conference for PhD studen ts in Civil Engineering
CE-PhD 2012, 4 -7 November 2012,Cluj -Napoca, Romania
www.sens -group.ro/ce2012

2. Particular cases in the development of road plantations

There are some critical situations in planning road plantations, such as:
– Arranging road plantations development on crests with vertical conv ex connections of
high gradients of the slopes (bumps);
– Arranging road plantations on the central island of roundabouts;
– Arranging road plantations on T -junctions between a main road and a secondary road

2.1 Road plantations on crests

In the case of crests , for a good perception of the route by road users, it is important for the type and
size of trees to be fully consistent with the geometry of the route. Fitting poor road plantations can
create feelings of trampoline. It is important that , in such situations, the tree crown height will
faithfully follow the road geometry without alternating the heights of the trees. By placing small
trees in the maximum peak of the route, followed by tall trees on the descent, the drivers perception
of the route to follow is disturbed, and the lack of adaptation of the driving speed to the trail
conditions often creates the effect of trampoline, even though in terms of geometric elements, the
route meets the standards.

Figure 2. Road crest

In these sectors is useful to plant trees in rows . The trees shall be size II or III (according to the road
plantation guidelines) , with a pyramidal port. Planting rows of trees is normally performed on the
safety zone on both sides of the road, placed symmetrically and paralle l to the axis of the road. To
enhance the guiding effects , untrimmed hedges can be planted in front of the row of trees. The
planting distances, between trees on the same row, shall be 50 m, in order to avoid the impact with

First International Conference for PhD studen ts in Civil Engineering
CE-PhD 2012, 4 -7 November 2012,Cluj -Napoca, Romania
www.sens -group.ro/ce2012

vehicles which could leave the carriageway. The hedge shall be of small or middle size, planted on
one or two rows and width shall be at most 100 cm.
The most productive trees to use on our roads are European Ash (Fraxinus excelsior), Field Maple
(Acer Campestre) or Silver Linden (Tilia Tomentosa) . For the hedges can be used Loncera,
Mahonia and Ligustrum.

2.2 Road plantations in roundabouts

In crossroads where the traffic circles, road plantations play an important role in carrying the traffic
in conditions of comfort. For proper op eration of the road, it is important that drivers entering the
crossroad focus on the crossroad without having insight into the route following the crossroad. This
can be achieved by illuminating the crossroad, the heightening of the central island fortifi ed with
proper planning of road plantations, to shorten the perspective on the route after the crossroad. In
this case, alignments of trees will not be planted near the turning point, to avoid creating a sense of
continuity on the road.

Figure 3 . Round about crossroad which needs road plantations

In the image above you can see that the entry into the turning point, the driver has an optimal field
of view (O.F.V) on the of stoplights of the vehicle that has already passed the crossroad, even if the
central island is heightened.
In conditions of night driving, without proper illumination of the road route, drivers tend to follow
the front vehicle stoplights. In the situation of a roundabout crossroad, it is necessary that through
the landscaping of the ce ntral island, in conjunction with a careful choice of road plantations, to
remove the vehicles that have already passed the crossroad, as well as the route after the crossroad

First International Conference for PhD studen ts in Civil Engineering
CE-PhD 2012, 4 -7 November 2012,Cluj -Napoca, Romania
www.sens -group.ro/ce2012

from view, drivers are thus forced to follow and be guided by the road signs, cr ossing the crossroad
conditions fluently.
On the central island, ornamental shrubs of low height shall be planted, which will obstruct the
vehicles on the main road. The most appropriate for this purpose is Pinus mug o, a small evergreen
dwarfed tree , formi ng a dense shrub. It has a size about 50 cm , with a slow grow rate.

Figure 4 . Roundabout with landscape [http://french -windows.blogspot.ro/ ]

2.3 Road plantations on junctions between main road and sec ondary road

When arranging road plantations at the junction of a main road located in a curb and a secondary
road prolonging the curve entrance alignment, it is important to avoid that the main road plantations
continue on the secondary road. In these si tuations, the driver’s attention focuses on the secondary
road, and they will not adjust the speed on the main road entering the curve or will mistake the
route. The situation is aggravated if the curve on the main road is not properly fitted (converted or
heightened).
To avoid these unpleasant situations, the curve on the main road will have a converted or
heightened profile and the main road will be outlined with isolated trees or shrubs. A continuous
trimmed hedge could also be useful.
The trees can ha ve globular or pyramidal crown. Recommended species are the mulberry tree
(Morus Alba, Morus Nigra), elderberry (Sambucus Nigra) , mahonia.

3. Conclusions

Road plantations must be located after a thorough study of the route, having an important role in t he
optical comfort of drivers and thus traffic safety. Marking the route through plantations, its visual
benchmarking, are important elements contributing to increased driver comfort, allowing him to
focus better on the road. Also, with an appropriate sett ing, road plantations may be protection
curtains against heavy snow falls and strong winds.

Acknowledgements

We appreciate the support of our scientific coordinator prof.dr.ing, Mihai Iliescu and the Technical
University of Cluj Napoca.

First International Conference for PhD studen ts in Civil Engineering
CE-PhD 2012, 4 -7 November 2012,Cluj -Napoca, Romania
www.sens -group.ro/ce2012

4. References

[1] Administrația Națională a Drumurilor – Instrucția privind plantațiile rutiere , ind. AND 561 -2001.

[2] Mihai Iliescu, Trafic și autostrăzi , UTCN, 1993

[3] M. Iliescu, F. Săvoiu, Considerații privind realizarea unor drumuri mai sigure, Conferința națională de
Materiale și Tehnologii Noi în Construcția și Întreținerea Drumurilor și Podurilor, Cluj -Napoca, 14 -15
Mai 2009, p. 45 -49

[4] *** STAS 4032 -1/2001 Lucrări de drumuri. Terminologie

[5] *** STAS 11210 -88, Lucrări de drumuri. Plantații ruti ere. Prescripții generale de execuție

[6] *** Traffic Safety Basic Facts 2010 Roads outside urban areas, DaCoTA Project