VISSIM 5.30-05 User Manual

6 The Traffic Network
Both, the location of the conflict marker (and thus the headway) and the
speed can be used to calibrate the acceptance of the “keep clear area”.
Example 3: Dual-lane roundabout with dual-lane entry
To model an entry of a roundabout several priority rules are necessary, each
of them serving different tasks. According to their difference in acceleration
capability and vehicle length cars and HGV/trucks/buses are dealt with
differently.
The following four illustrations visualize all the priority rules according to their
task. For easy reference the rules are numbered. The numbers refer to small
boxes within the illustration where the corresponding parameters can be
found. The values used for min. gap time, min. headway and max. speed
have been determined through research. Thus for most applications these
serve as a realistic base.
Place priority rules according to the following criteria (cf. illustrations):
► Stop lines represent the typical waiting position. If more than one green
bar refers to the same stop line it is important to model them as multiple
green bars to the same red bar (not as separate priority rule pairs) as
long as the conditions for the red bar are the same. E.g. it is not possible
to combine two red bars into one if they have different vehicle classes
assigned.
► Conflict markers used for headways are to be placed shortly before the
position where the connector enters the roundabout link (if they would be
placed after the entry of the connector it could result in a situation where
a vehicle would wait for itself and thus drastically reduce capacity of the
roundabout).
► A green bar used for min. gap time only should be placed around the
same distance away from the conflict area as the associated stop line.
266 VISSIM 5.30-05 © PTV AG 2011