Dissertation-Endstand3 - KLUEDO - Universität Kaiserslautern

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