8/10/2019 laa.pdf

1/17

D.Sc. Toma TOLLAZZI, Full Professor

TURBO ROUNDABOUTS

INVITED LECTURES

Faculty of Civil Engineering

8/10/2019 laa.pdf

2/17

What is turbo roundabout?

-partially traversable centre island and with a spiral circulatorycarriageway, where into three or more roads enter, with multiple centres

The turbo roundabout is an innovative arran ement of the two lane

carriageway)

roundabout that has revolutionised roundabout design in The Netherlands.The turbo roundabout is a specific kind of spiralling roundabout that wasdeveloped by Mr. L.G.H. Fortuijn.

Turbo roundabout is a special type of the two lane roundabout, wheresome direction flows are separated or run on physically separated lanes.

8/10/2019 laa.pdf

3/17

In the turbo roundabout the traffic flows run separately even before the

throughout the roundabout, whereas traffic flows run separately also atthe exit from the roundabout.

into the inner roundabout traffic lane.

8/10/2019 laa.pdf

4/17

Physical separation is achieved by specially shaped elements, which

8/10/2019 laa.pdf

5/17

The turbo roundabout has a bigger capacity, compared to the normal-

at the roundabout entry of this type, there are usually two traffic lanes,which directly continue into two circulatory traffic lanes, the use of the inner circulatory traffic lane becomes more attractive,since there is no need for weaving, the entr traffic flow is no lon er hesitant when enterin the circulatorcarriageway, which increases the capacity of entries.

8/10/2019 laa.pdf

6/17

The turbo roundabout has a higher level of traffic safety, compared to the -There are several reasons for that. The most important is lower numberof conflict points!

MergingMerging

CrossingCrossing

8/10/2019 laa.pdf

7/17

DRIVING RULERS IN THE TURBO ROUNDABOUT

Phisical separation of traffic flows requires the driver to decide on thedirection of exit from the roundabout or to select an appropriate trafficlane already at the entry into the roundabout or even a little before theentry.When the driver, before entering the turbo roundabout, decides on whichexit he shall leave the roundabout, he can no lon er chan e his decision.Namely, the driver must choose an appropriate traffic lane even beforethe entry into the roundabout, because the turbo roundabout does not

ermit chan es of traffic lanes in the circulator carria ewa !

8/10/2019 laa.pdf

8/17

Possible directions of driving within the roundabout and possible exits

signs at the portals.

Drivers should be assisted by clear signposting and lane marking - aspec a orm o arrow mar ng as een eve ope or ur oroundabouts, which makes for clearer lane selection!

8/10/2019 laa.pdf

9/17

CONDITIONS AND LOCATIONS OF APPROPRIATE USE

e tur o roun a out s an appropr ate so ut on on ocat ons outs e t eurban areas, when there is normally one main and one side traffic route,regarding the intensity of the traffic flows.

The turbo roundabout in the urban area is just a conditionally appropriate

solution. If a roundabout with two entry and two exit lanes is considered,which would be located in the urban area we must first solve the problem of traffic-safe leading of non-motorised traffic participants .

of:- existing traffic-overloaded one-lane roundabouts, the size of whichou er ra us ena es e mp emen a on o an a ona c rcu a ory

lane inwards (better solution) or there is space for the implementation of

another circulatory lane outwards (somewhat less appealing and more,- existing traffic-overloaded two-lane roundabouts,- existing traffic less safe two-lane roundabouts,

- reconstruction of the classic intersection with a predominant main trafficdirection, with a very strong traffic flow.

8/10/2019 laa.pdf

10/17

GEOMETRIC DESIGN ELEMENTS OF THE TURBO ROUNDABOUTS

- turbo block.

This is a block or a formation of all the necessary radii, which must berotated in a certain way, thereby obtaining traffic lanes or driving lines.

The size of radii of the standard roundabout with a spiral course of the

be selected in a way that the speed of driving through the roundaboutdoes not exceed or equals 40 km/h!

8/10/2019 laa.pdf

11/17

8/10/2019 laa.pdf

12/17

POSITION OF THE TRANSLATORY AXLE AND CONTROL OF THETURBO BLOCK POSITION

The turbo block contains (besides all radii) also the so-called translatoryaxle. A translatory axle is an axle, whereon the movement of certain radiiis carried out.

The best position of the translatoryaxle is as if the clock hands pointed

five minutes to five oclock in thecase of four - armorten minutes past eight oclock in

-

turbo roundabout!

8/10/2019 laa.pdf

13/17

From this step, the procedure is nearly the same like in normalroundabouts!

At the end a short comparation of prices (expences):- this comparation is stupid because every case is unique- ,- depends also of the dimensions of the working areas- ...

But, however:2008 2009 2010 2012

''Standard'' double lane

the duration of construction

4 5 months 4 5 months

indicat ive pr ice 800.000 1.500.000,00 600.000 1.100.000,00Turbo the duration of 5 months 5 6 monthsroundabout construction

indicat ive pr ice 800.000 1.650.000,00 500.000 1.200.000,00

So, we can conclude that, in global, turbo is a little bit more expensivesolution than standard double- lane roundabouts (10 15 %)!

8/10/2019 laa.pdf

14/17

, ,roundabouts:

- - Slovenia 11- Germany 1- Hungary 1- Belgium 1-

8/10/2019 laa.pdf

15/17

Germany: Baden Wrttemberg (without kerbs, just painted bad experiences)

8/10/2019 laa.pdf

16/17

Hungary: city Szolnok; from 2009; too much divided kerbs bad experiences!

8/10/2019 laa.pdf

17/17

Indiana (USA): city Carmel very good experiences in both turbo