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An end to road traffic chaos at road junctions

  • 14-04-2019 4:43pm
    Registered Users Posts: 1,667 ✭✭✭ Impetus
    Registered User

    The Diverging Diamond Interchange (DDI) was invented in France, and copied by many cities in the US. The concept can be used for both complex motorway interchanges as well as ring roads (peripheriques) and ordinary national roads with busy junctions.

    It reduces accidents by about 60% compared with conventional junctions. The capital cost of a DDI is about 50% of a conventional interchange. DDI delivers the most efficient interchange possible, and can be combined with AI (artificial intelligence controlled traffic signals) to automatically adjust signals for every eventuality from 04h in the morning to 17h in the afternoon, minimising traffic delay.

    It involves guiding the traffic to the other side of the road temporarily while the vehicles transit the core of the intersection. After crossing to the other side of the junction the vehicles return to the normal driving side. All movements are protected by signage, physical pathways (barriers) and two phase traffic signals. Please see the video.

    Two phase traffic lights control the entire junction. Where traffic lights are used in Ireland they often have four or five phases, which gives very little green time for many junction approaches. Bridges in particular are a nightmare because the timing of the lights on one side of the river has an impact on the traffic flow so both sides of the river have to be synchronised which in turn leads to a few seconds of green, and then back to red with resulting tail backs.

    Enter the DDI interchange. You can divide the time 50% green and 50% red, at all lights – or 60:40 or whatever is appropriate for the traffic at a time of day.

    Please see the video below. This video looks at a highway interchange. The same design could work in a city street or bridge, given space, with modification of the scale of the DDI. The junction has to be executed as a mirror image of the examples in this video because all instances of DDI implementation have been in countries with LHD vehicles.

    The existing SCOOT and SCATS traffic signals used in Ireland are based on 50 year old technology which is not fit for purpose in 2019. Ditto for junction designs which are variations of an old fashioned crossroads on a country bohareen. Tinkered with instead of reconceived for the 21st century. And Pig inefficient. And so it goes on because nobody seems to care about having to sit in traffic chaos, virtually every day of the week.

    Or more probably there is such a disconnect between the person in the car, ie the voter, and the people who manage the urban roads in a dysfunctional state such as Ireland, where there is no direct democracy, and local government is as disconnected from the system as one can get. Not that one blames the latter – local politicians get paid a pittance for the job. Having said that, the system is broken, and is not delivering the travel environment that society needs. Neither in Ireland’s downmarket broken public transport non-system, nor in road traffic management.