Dissertation-Endstand3 - KLUEDO - Universität Kaiserslautern
Dissertation-Endstand3 - KLUEDO - Universität Kaiserslautern
Dissertation-Endstand3 - KLUEDO - Universität Kaiserslautern
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4<br />
ABSTRACT<br />
Prioritisation for public transport modes at<br />
roundabouts<br />
Since the early 1990s, several new roundabouts<br />
were built all over Germany. Particularly the reconstruction<br />
of former traffic light junctions into roundabouts<br />
is evaluated as being advantageous for car<br />
traffic. However, advantages for car traffic means<br />
disadvantages for public transport modes in this<br />
context. The effects of roundabouts on the operation<br />
of public transport are partly tremendous.<br />
Such effects are:<br />
• Time losses for public transport vehicles at<br />
roundabouts are extremely variable.<br />
• Driving through the roundabout is connected<br />
to a lack of comfort for passengers.<br />
• Prioritisations for public transport modes at<br />
roundabouts are uncommon.<br />
• Possibilities for prioritisation at traffic lights<br />
do not work with roundabouts.<br />
Prioritisation and acceleration of public transport<br />
modes along road networks with roundabouts,<br />
however, is possible. This has been proved by<br />
empirical evaluations as well as simulations.<br />
Measures for acceleration at roundabouts with low<br />
traffic volumes is not necessary. In addition, such<br />
measures are related to an unfavourable costbenefit<br />
ratio.<br />
If high traffic volumes exist on the access roads an<br />
extra lane for public transport along those roads<br />
has large scale effects on acceleration. However,<br />
two separate parallel lanes for car traffic and buses<br />
lead to irritations between both transport modes at<br />
the roundabout. When the two lanes switch to a<br />
single entry lane right before the roundabout such<br />
irritations did not occur. The latter alternative has<br />
the special German acronym ‘KREIFAS’ i.e.<br />
roundabout with special drawn-in lanes. The car<br />
traffic changes lanes while buses are able to go<br />
straight forward.<br />
Another possibility to accelerate public transport at<br />
roundabouts is the so-called ‘sleeping traffic light’.<br />
Whenever a bus or tram approaches the roundabout<br />
a special red light stops car traffic affecting<br />
the bus route. Other vehicles in front of the approaching<br />
bus also benefit from this measure.<br />
These measures as well as a catalogue of additional<br />
measures are able to reduce waiting time for<br />
buses at roundabouts. A side effect is the homogenisation<br />
of vehicle movements approaching the<br />
roundabout, which also helps obeying the timetable<br />
and leads to higher comfort on board the bus.<br />
As a whole, concerning roundabouts, it is necessary<br />
for a planning process to take all transport<br />
modes into consideration. The requirements of<br />
public transport modes at roundabouts must be<br />
considered accurately throughout the planning<br />
process.<br />
Hence, prioritisation measures at roundabouts are<br />
able to compensate missing measures at traffic<br />
light crossings.