On my local primary route, the A10, two sets of traffic lights have been put in recently, at Butt Lane and Denny End Junction. In my mind, they're a bad idea, but that's me . Anyway, they are both 3 way junctions, with the A10 the main road going straight through and minor roads into Histon for the Butt Lane junction (although most traffic to Histon uses the B1049 off the A14) and Waterbeach for the Denny End junction. Instead of having two phase lights (one phase for traffic on the main road, the other phase for traffic on the minor road), they are 3 phase.
Now, coming northbound on the A10, the minor road turn off at Denny End Junction is on the right. I'll use this example rather than Butt Lane. Phase 1 is for traffic on the main road to go straight or turn left - no turning right onto the minor road. The second phase is for traffic on the northbound side only - traffic on the southbound side is stopped. The third phase is for traffic on the minor road to turn either left or right. The first and second phase bug me - having this system means that traffic backs up on the A10 southbound backs up at busy times. I think if traffic lights are absolutely essential here, they should be two phase to let A10 southbound traffic flow - and there is a lot of it in the morning heading down to Cambridge.
My question is - is there some kind of discouragement of two phase signal these days?
Two Phase Traffic Lights
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- PeterA5145
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Surely the purpose of having three-phase lights at T-junctions is to provide a specific phase for vehicles turning right from the main road to the side road. Otherwise they would have to wait for a gap in the oncoming traffic and a tailback could develop.
This kind of arrangement is very common and where there is a substantial right-turning flow entirely sensible.
This kind of arrangement is very common and where there is a substantial right-turning flow entirely sensible.
“The human race divides politically into those who want people to be controlled and those who have no such desire.” – Robert A. Heinlein
Re: Two Phase Traffic Lights
Three phase lights ban turning traffic from being in the junction whenever conflicting traffic is allowed to enter it, so remove one potential cause of accidents.tommyd49 wrote:My question is - is there some kind of discouragement of two phase signal these days?
If the main road is too narrow for turning lanes, waiting turning traffic can also block through traffic, so that the second phase needs to be much longer than turning traffic needs by itself. The three-phase lights at the crossroads in Northop are like this, giving northbound traffic a phase to itself.
I don't know how wide the A10 is by here, however.
- sotonsteve
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A crossroads near my house was converted from three phase to four phase. The phases were originally along the main road in both directions, allowing vehicles to turn left and right at the same time. The other two phases were for the two side turnings. With the modification cars on the main road cannot turn right without oncoming traffic being stopped at red lights and a right turn green arrow lighting up.
The junction used to flow fine, but now the phasing has been altered the capacity of the junction is lower and congestion is more common. I wished they could have applied the logic of "if it ain't broke don't fix it". Policy nowadays is "let's make life harder and squander taxpayers' money at the same time".
The junction used to flow fine, but now the phasing has been altered the capacity of the junction is lower and congestion is more common. I wished they could have applied the logic of "if it ain't broke don't fix it". Policy nowadays is "let's make life harder and squander taxpayers' money at the same time".
The problem is while it gives the traffic turning right from main road to side road a certain chance to get out, it causes big problems for traffic heading south on the A10, having to stop for a long period of time. Whilst at the Denny End junction (not at Butt Lne though), there is a fair amount of traffic turning on and off Denny End Road, the fact is the lion's share of traffic on the A10 heads straight. So the 3 phasers cause bigger tailbacks than if the junction had 2 phasers (or no lights at all ).PeterA5145 wrote:Surely the purpose of having three-phase lights at T-junctions is to provide a specific phase for vehicles turning right from the main road to the side road. Otherwise they would have to wait for a gap in the oncoming traffic and a tailback could develop.
This kind of arrangement is very common and where there is a substantial right-turning flow entirely sensible.
Re: Two Phase Traffic Lights
No, just plenty of idiots trying to play at being traffic signals engineers.tommyd49 wrote:My question is - is there some kind of discouragement of two phase signal these days?
After all, theyre only bulbs at the end of a bit of wire arent they...