WHAT MAKES A JUNCTION UNSUITABLE
Main junctions are typically “not a problem”, because the centre median strip that divides the highway would be capable of help the pair of site visitors lights: The usual site visitors gentle and the brand new red-amber-green arrow gentle.
“As a best practice, we will definitely try to put a pair (of lights) on the centre median. But sometimes we can’t due to site constraints, especially at older roads or junctions, where we just can’t install anything on the median. That’s a bit challenging,” mentioned Mr Png.
“Or some medians are too narrow; you can’t widen it further (due to site constraints) to accommodate that extra red-amber-green traffic light.”
Slender junctions or junctions with “a single lane or limited lanes” additionally pose a difficulty, “especially if it’s a busy junction”, he famous.
“At red-amber-green junctions, you’re not allowed to turn right even if there is no opposing traffic or pedestrians crossing. So if the lanes are limited, right-turning traffic waiting to turn right would obstruct the through traffic,” he defined.
If such a junction is taken into account “unsafe”, but the highway can’t be widened or have extra lanes added, the site visitors gentle sequence would possibly have to be modified, added Mr Png.
“You might have to give that approach a dedicated green time, so both through and right-turning traffic can go at the same time. But that will also result in trade-offs in terms of delays to other approaches.”
One other doable answer is an “overhead” red-amber-green arrow, which LTA has presently applied at some such junctions.
“What we do is modify the red-amber-green arrow at those locations, so that the overhead red-amber-green traffic lights are horizontal instead of vertical. This eliminates any civil works on the centre median which then reduces burden on contractors and disruption to traffic,” he mentioned.
Present roads with overhead red-amber-green arrows embody the junctions of Bishan Road 13 and Road 14, Bencoolen Road and Center Highway, and Jurong East Avenue 1 and Road 21.
REDESIGNING ONE JUNCTION AFFECTS OVERALL TRAFFIC
Nonetheless, Mr Png acknowledged that after a discretionary right-turn junction will get a red-amber-green arrow, there will probably be “some trade-offs” and “mitigation measures” could should be launched.
“It could be something as simple as changing the phasing or the sequence of traffic lights. It could go even further where civil works are necessary,” he mentioned.
“We look at what’s the most optimum design. Because with every change, there are multiple variables which change. Everything is related to everything else. It’s an iterative process; you have to run the simulation, change the design, run the simulation (again), then come to a steady state of optimisation.”
Your entire course of may take a few months with civil works, particularly the place there’s a must do trenching of underground pipes with a purpose to lay new cables.
“It all depends on whether there are enough cables, because if not, you might have to dig a trench to lay pipes, pull the new cables and then connect to the controller. But if the junction has enough cables, then certainly it’s faster,” he added.
Drawing on an analogy to clarify how the group manages the trade-offs concerned through the design course of, Mr Png likened a site visitors gentle cycle to a pie from which motorists and pedestrians combat for a slice. This slice represents the period of time one has to navigate by the junction.
A site visitors gentle cycle is the whole time required for the sunshine to serve all sign phases.
“The trade-off for red-amber-green arrows is delays. The slice of the time is more (with a red-amber-green arrow), changing the proportion of the other slices of the pie,” he mentioned.
“If one person is asking for more time, I need to give a bigger slice of the pie and that could be at the expense of another person. It could be the pedestrian or it could be traffic in the opposite direction that’s in conflict. If you increase one portion, you decrease another portion.”
And if everybody wants extra time, the general dimension of the pie will increase. If the rise is “too much”, then the ready time on the junction turns into longer. This might then have an effect on the subsequent junction as it will additionally must run with the identical site visitors cycle, as a result of “it’s all synchronised”, he added.
“In order to achieve synchronisation, every junction must have the same (corresponding) size of pie throughout the entire road corridor downstream. As a road user, they will then feel frustrated if they sense that they are waiting longer than necessary.”
That mentioned, motorists ready for the inexperienced arrow through the wee hours, for example, would expertise a shorter ready time than in the event that they have been on the identical junction throughout peak hours.
Singapore’s roads have dynamic site visitors phasing because of the Inexperienced Hyperlink Figuring out (GLIDE) system, which adjusts the inexperienced time as site visitors stream modifications.
With GLIDE, loop detectors embedded within the highway lanes are used to detect the presence and depth of auto and pedestrian site visitors, triggering site visitors sign changes.
“With off-peak hours, like wee hours of the night, your slices of the pie can be smaller because there is lesser demand for time at the junction, hence the (total) cycle time is smaller. That reduces the frustration of waiting,” defined Mr Png.
“We’ve also introduced repeated right turns at some junctions – within the cycle time that you have, two opportunities to turn right. And if there’s no traffic for an approach, then I could give that slice of time to another approach that needs it.”
With motorists at these redesigned junctions forbidden from making discretionary proper turns, nevertheless, Mr Png hopes that pedestrians do not take their security as a right and pay much less consideration when crossing the junction.
He cautioned that “mistakes can still happen” regardless of the red-amber-green arrow, which isn’t a silver bullet to eradicating site visitors accidents.
“The entire driving experience from your home or car park to your destination is a discretionary activity, not just the right turn,” he added.
“Whether you look out for traffic, or decide to turn right or left when you come out of the car park, switching lanes, every time is a discretionary decision.”
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