Week 2 - Roundabout intersections Flashcards
what is a normal roundabout
kerbed central island less or equal to 4m diameter
flared entries and exits
what is a mini roundabout
has a circular island of diameter less than 4m
what is a double roundabout
contains 2 roundabouts separated by a short link
what is a grade separated roundabout
what is a signalised roundabout
includes traffic signals on more or more approach roads
operated full time or part time
what does roundabout selection depend on?
whether the approach roads are single or dual carriageway
road speeds
traffic flow
level on NMU flow (non-motored user)
what is entry path curvature?
radius measured over 20-25m length, no more that 50m from the give way line
what is entry width and approach half width
entry width - largest factor that effects capacity
approach half width - width of the approach carriageway including hatching
what is effective flared length and sharpness of flare
effective flared length - average length over which the entry widens
Sharpness of flare - a measure of the rate at which extra width is developed in the entry flare depending on the available land take and capacity
what is entry angle?
geometric substitute for the conflict angle between entering and circulating traffic streams
what is the recommended width of the circulatory carriageway?
1.0 to 1.2 x maximum entry width
what is the preferred calculated rate of flow capacity of priority junctions or non signal roundabouts?
85%
what is RFC
rate of flow capacity
what is DoS
degree of saturation
what is maximum calculated level of DoS for a signal controlled junction
90%
