rev wrote: ↑
Mon Aug 20, 2018 9:57 am
SBD wrote: ↑
Sat Aug 18, 2018 12:39 pm
rev wrote: ↑
Sat Aug 18, 2018 11:23 am
The problem with that is the timing of when the red arrow turns off. What's the point of it during peak hour traffic periods? As you said, max two vehicles will get through.
Right turn from southbound Main North Road into Regency Road gets two turns per cycle (evening peak anyway). There's a green arrow which goes red before northbound traffic is let through. Later, the red arrow goes out, and one or two more cars (or more depending on the timing of gaps in northbound traffic) get through. It seems to work there.
That's not the case everywhere though.
Another example. Torrens Road/South Road-T2T intersection..
The distance to turn from Torrens Road onto South Road is now quite large. The time the green arrows stay on is so small, only 2-3 cars manage to get through, 4 if all the drivers are switched on and get a move on and the last guy runs through the yellow as it turns red.
During peak hour, when there's cars banked up in the right lane, because there's cars waiting to enter the turning lane, that's not sufficient and causes congestion.
The turning lanes will never be a couple hundred meters long, so there will always be a spill of cars waiting to get into the turning lane during peak hour.
Why don't they change the sequence so when the green light comes on for traffic going straight, the green arrow turns on and stays on, then they both go yellow/red together. Wouldn't that help traffic flow smoother with less delays?
They do have different sequences in different places, I guess they are set according to the anticipated traffic flows, but I have no idea how often they can be reviewed or how complex they can be for different times of day.
Your example is close to how the Main North Road and Curtis/Craigmore Road intersection works. There are left turn slip lanes on all sides.
* Northbound goes green, including north-east right turn arrow (this phase is skipped if no cars queued to turn)
* Right arrow changes to red, southbound gets red arrow and green circle
* northbound goes red, south-west arrow goes green (this phase is skipped if no cars queued to turn)
* all MNR gets red, Curtis eastbound gets green, including arrow
* Curtis gets red, Craigmore westbound gets green including arrow
I don't know if the east/west phases merge if nothing is queued to turn either side as I don't think I've ever seen it.
RIght turn lane from northbound has recently been extended, so doesn't block through traffic as much now. Right turn from Curtis (eastbound) has two lanes but still fills up.
As well as the general timing constraints, I think there may be a monitor to watch the queue for the railway crossing further back Curtis Road as I don't think the right turn arrow lights on MNR if the road is full.
Main North and Womma/Tolmer Roads is different.
* Both Main North right turn arrows go green
* There are sensors in both right turn lanes; as they empty, the arrow goes red and opposing straight on gets green (these seem to change in either order, depending on traffic)
* Main North has green both ways
* Womma gets straight and right
* Tolmer gets straight and right