Highway Engineering

on the approach to a signalised intersection is 3.25 m. At this value, assum-

ing zero gradient, the saturation flow for nearside lanes is set at 1940 pcu/hr,

increasing to 2080 pcu/hr for non-nearside lanes.


 Weather conditions

In wet weather conditions, saturation flows decrease to 6% below their dry

weather values.

 Gradient

For every 1% increase in uphill gradient (measured over a 60 m distance back

from the stop-line) the saturation flow value will decrease by 2%. Downhill

gradients do not affect saturation values

134 Highway Engineering

Stage 1

N-S: green

E-W: red

Stage 2

N-S: red

E-W: green

N

Figure 5.28Typical stages within a two-phase system.

Stage 1

N-S: green

(no right turn)

E-W: red

Stage 2

N-S: green

(right turn only)

E-W: red

Stage 3

N-S: red

E-W: green (all

movements)

Figure 5.29Typical stages within a three-phase system (two lanes each direction with a

dedicated lane for right-turning vehicles in all cases).