Traffic Control Signals and Power

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jpoc

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#931816 13-Nov-2013 08:04

scuwp: I am not a traffic planner or engineer, but I know plenty. Roundabouts trump lights every time for safety, however roundabouts also have a limit to the traffic volume they can handle before they become inefficient (i.e. huge delays and traffic jams), they also take up more land which could equal increased capital cost, consent issues etc.

Power supplies these days are for the most part very reliable. Cost benefit for UPS won't stack up at all IMO.

You are partly correct but you have missed a couple of important factors.

Regarding the traffic limit, the UK has known for a very long time how you sort this one out. Where you have two four lane roads crossing, you lay things out so that folks turning left can do so all the time with no need to give way. If you cannot do that or if doing it does not solve all of your problems, you put lights on the roundabout and activate them for two hours a day or whatever your local traffic patterns require.

Regarding the space required, you can put a mini-roundabout in just about anywhere. All that you need is to paint a circle on the road in the middle of the junction, paint the appropriate give way markings on the road and erect some signs. It is not necessary to increase the road surface.

trig42

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#931855 13-Nov-2013 09:03

When the power went out yesterday, I watched the intersection on St Lukes road (outside the mall) and I thought the traffic flowed quite well, people were courteous and let people through, there were no major backups and I heard no horns.

Impressive I thought.

Behodar

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#931870 13-Nov-2013 09:11

Going slightly off topic here, but it's still about traffic lights :)

When they were doing some roadworks here in Whakatane, they set up temporary lights. A couple of seconds before changing to green, they'd go both red and orange. (ie. green > orange > red > red and orange > green). This gave you a couple of seconds to turn the brake off etc, making the traffic flow immediately on green and saving a couple of seconds.

Why don't they do that everywhere?

E3xtc

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#931875 13-Nov-2013 09:21

These are similar to lights in the UK - which go green > orange > red > orange > green....I thought they work perfectly well as there is less lag as people visually are aware (assuming they are looking at the lights and not their phone/makeup/book/etc) that the lights are going to go green.

I wonder if it would cut down on people running orange/red lights too - as people would quickly become aware that as soon as the light turns red the other traffic will be flowing

BlakJak

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#931910 13-Nov-2013 09:50

Dislike red-orange-green-orange-red. Status quo means Orange has no ambiguity; it's 'stop if it is safe' not 'figure out whether it's about to go red or green first, then...'

Driver education is the key, but for a lot more than traffic lights and roundabouts!
I'm a big fan of Roundabouts but they don't work if you have dominant flow from one direction (which can lead to the next intersection to the left basically never getting a turn) and they also do have a choke point regarding volume. Unfortunately Traffic Lights seem to be the golden bullet used everywhere, and yes, too many motorists competely lose it when the lights are out.

Speaking as someone who's done point duty and traffic control more times than he can count, you really do have to assume that all motorists are stupid, and plan with that in mind. It's the only way that's safe.

And many years ago MOT used to replace traffic lights during peak times to manually adjust flows for efficiency. The argument seems to be that this is no longer reasonable. Sad, because it also meant they were familiar with the intersection and could take over easily in the event of a power failure.

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hoogy

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#933250 13-Nov-2013 15:45

Roundabouts are also bad for non-motorised road users. Poorly designed roundabouts can make to very difficult for pedestrians to cross the road. Cyclist safety is also poor with NZ roundabouts, we would need Dutch roundabouts. Roads are not for moving cars but for moving people and things.

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BlakJak

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#933276 13-Nov-2013 16:18

If crossings are incorporated, Roundabouts are fine (just don't expect a diagonal crossing!)

Most of the problems with cyclists and roundabouts can be attributed to driver ignorance.

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Mark

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#933366 13-Nov-2013 17:33

When the power went out the length of Great North Road the other day, some of the bigger intersections got very interesting! I was wondering why they had no redundancy since they are mostly LED based now.
Same goes for the street lights .. be nice if they had a low power LED spot light in the light shroud for when main power goes off, a little light is better than nothing.

I personally think a simple UPS in each pole would not be that hard to manage and shouldn't add too much to the cost of each unit .. though government agencies do tend to pay over the top for things.

BlakJak

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#933384 13-Nov-2013 18:05

Trust me that UPS's are more expensive than they seem when you're installing a large number of them, and can make life less reliable than mains alone. Seen this many times on large campuses.

If nothing else you'd have a team of people constantly replacing worn-out batteries!
How often are the lights out for any duration? I doubt the cost:benefit ratio is there to justify the maintenance overheads.

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Mark

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#933992 14-Nov-2013 16:35

Well for the outage I described it was about 5 hours ... and judging by the amount of glass on the road one or two people did not manage to navigate the traffic light free junction.

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