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Triangulation

PostPosted: Sun May 03, 2009 9:17 pm
by brianhaddon
Near where I live is a single lane two way road that adjoins a two way two-lane single carriageway. The design of the junction is as a triangle. For years either 'leg' was two way then a few years ago a keep left arrow appeared for traffic exiting the single lane road as the right hand leg (for them) entered the road 'blind' as it is on a bend. To me this inferred that that leg was effectively one-way to be used as an entrance to the road, but the other leg was two-way as there were no no-entry signs or other arrows. There is a give way line at the end of the left leg as you exit but on the other leg a give way line as the two legs join (if you get my drift). Common sense says to use the legs as one-way, one for entry one for exit but they are just long enough not to be used that way (and not signed as such) and commonly not used that way either. My question is - what are the rules regarding such junctions and what signs should there be?
Regards
Brian Haddon

Re: Triangulation

PostPosted: Sun May 03, 2009 10:55 pm
by fungus
In the village where I live, there is a short spur to the left that avoids going on another 20 yds or so and making a 90 degree left turn. The spur is one way, as indecated by a single broken white line across the entire width of the road. There is no one way sign, but at the opposite end there is a NO ENTRY sign for drivers approaching from the road to the left. At that end of the spur, the road markings are a single broken line. This in my mind is incorrect, as give way markings are always a double broken line, except at roundabouts.

Nigel ADI
IAM trainee observer

Re: Triangulation

PostPosted: Mon May 04, 2009 1:29 am
by kfae8959
Doesn't it depend on the traffic you've got to give way to? Single dotted give-way lines indicate that traffic must give way to road users in one direction; double lines indicate that two directions must be considered. In the example of a plain T-junction where users approaching up the leg must give way, the double lines indicate that they must give way to traffic in both directions on the main road; the single line indicates that traffic joining from the main road must give way to any road user already using that lane (pedestrians crossing, for example.) Approaches to roundabouts are marked with single give-way lines because, by definition, there is only one stream of oncoming traffic to take into account.

Re: Triangulation

PostPosted: Mon May 04, 2009 7:24 pm
by fungus
In the example I have given, there are no road markings or road signs, prohibiting drivers turning right at the end of this short spur, and effectively making a U turn by going clockwise around the triangle.

Nigel ADI
IAM trainee observer

Re: Triangulation

PostPosted: Tue May 05, 2009 12:24 am
by kfae8959
fungus wrote:the road markings are a single broken line. This in my mind is incorrect, as give way markings are always a double broken line, except at roundabouts.


...was what I took to be your decisive point, to which I responded. I wonder how the example you give might be considered similar to joining a roundabout?

David

Re: Triangulation

PostPosted: Wed May 06, 2009 2:22 pm
by fungus
You've got me worried now. I've just found the image on Google Earth, and it seems there is a double broken line at the NO ENTRY end. I must check next time I pass.

Nigel ADI
IAM trainee observer

Re: Triangulation

PostPosted: Wed May 06, 2009 5:52 pm
by 7db
Brian --
I think I've understood the layout. Does traffic turning right out of the minor road need to go left,then cross the inbound entrance to the left leg and o a sharp turn out onto the major road? Sounds like hard work.

Otherwise the two legs are natural to aid drivers coming in off the major road from left or right directions to have a less steep turn.

What are the end marking on the LH leg? Is it part double (outbound) part single (inbound) dotted white line?

In terms of the required signage -- the keep left and no-entry uprights are the ones that are used to convey legal meaning. The paint is just a slippery reminder.

Re: Triangulation

PostPosted: Wed May 06, 2009 8:39 pm
by brianhaddon
7db wrote:Brian --
I think I've understood the layout. Does traffic turning right out of the minor road need to go left,then cross the inbound entrance to the left leg and o a sharp turn out onto the major road? Sounds like hard work.

Hi Dave,
Not quite - It goes left, but then makes a sharp right turn on the major road.


7db wrote:What are the end marking on the LH leg? Is it part double (outbound) part single (inbound) dotted white line?

The marking is double (as for outbound) but it is a single lane. There are no 'No Entry' signs. If you look on Google Earth - coords 52 degrees 49 mins 56.38 secs N, 1 degree 31 mins 29.50 secs W (Dunno how to do degree sign on here :oops: ) You will find the junction, in Milton, Derbyshire. There is a keep left arrow hidden by the tree in the photo for traffic leaving the single lane. That apart from the paint is the only clue of directional preference.

I actually think traffic approaching to turn right into the lane can legally use both legs by the signage. I was wondering what others thought.

Regards
Brian Haddon

Re: Triangulation

PostPosted: Wed May 06, 2009 10:50 pm
by fungus
Brian, I have just looked on Google Earth at Milton Derbyshire. I presume that the junction in question is the one in the High Street at the southern end of the village. The branch that turns north,to the left is, (in my oppinion,) one way out of the side road, as indicated by the double broken line, which alows the driver to turn left or right at the end. The southern branch with the single broken line is one way into the road. I presume that there are NO ENTRY signs at the end of the northern branch facing drivers on the High Street prohibiting entry. Likewise I presume that on approach to the southern end from the side road, NO ENTRY signs prohibit entry to the High Street.

I have checked the junction in the village of Corfe Mullen where I live, and the image on Google Earth is an earlier image. The angled junction definately has single broken lines where it meets Wimborne Rd.

To view the image, go to Google Earth. Type in Wimborne Road Corfe Mullen Dorset. Scroll approximately south until you meet the juntion with the B 3074 Blandford Road. You will see the triangulation. Entry is permitted from the Blandford Road, but not from the Wimborne Road. There are NO ENTRY signs facing drivers on the Wimborne Road, but the road marking is a single broken line, not a double broken line as shown on Google Earth.

Nigel ADI
IAM trainee observer

Re: Triangulation

PostPosted: Thu May 07, 2009 12:41 am
by brianhaddon
fungus wrote:Brian, I have just looked on Google Earth at Milton Derbyshire. I presume that the junction in question is the one in the High Street at the southern end of the village.

Correct.
There are not any NO ENTRY signs. There is only one sign and that is a keep left arrow at the point where the road splits when coming from the lane. In the Google Earth photo it is hidden under a tree.

Also the road is a single lane track barely wide enough for a car, so is each leg.
Regards
Brian Haddon

Re: Triangulation

PostPosted: Fri May 08, 2009 1:03 pm
by fungus
Brian,

The keep left sign to which you refer, I would imagine, is the blue disc with a white downward facing arrow pointing left. Are there signs prohibiting turning into the northern branch, from the High Street? If so, I would imagine that the LA thought that lines on the road would suffice.

Nigel ADI
IAM trainee observer

Re: Triangulation

PostPosted: Fri May 08, 2009 7:26 pm
by brianhaddon
fungus wrote:Brian,
The keep left sign to which you refer, I would imagine, is the blue disc with a white downward facing arrow pointing left.

Yes

fungus wrote:Are there signs prohibiting turning into the northern branch, from the High Street?

No, the only sign is the keep left one I mentioned on the lane where it splits for traffic coming down the lane. Other than that sign there are no other signs.

Regards
Brian Haddon

Re: Triangulation

PostPosted: Fri May 08, 2009 10:37 pm
by fungus
Brian,

I always understood that double broken lines that stretch across the entire width of the road indicated that the road was one way, and that you could not enter from that end. A single broken line indicates that you can enter from that end.

As far as the regulations are concerned, I do not know if the road markings should have a road sign backing them up, or not. Perhaps someone in that department will be along to answer that one soon.

Nigel ADI
IAM trainee observer

Re: Triangulation

PostPosted: Sat May 09, 2009 6:46 am
by Gareth
fungus wrote:I always understood that double broken lines that stretch across the entire width of the road indicated that the road was one way

The HWC just says the lines themselves mean emerging traffic should give way to traffic on the major road. Know your traffic signs gives no further information. Given there's no prohibition for crossing unbroken lines irrespective of the direction of travel, I'd be surprised, (and enlightened), if your interpretation was correct.

Re: Triangulation

PostPosted: Sat May 09, 2009 8:46 am
by brianhaddon
Gareth wrote:
fungus wrote:I always understood that double broken lines that stretch across the entire width of the road indicated that the road was one way

The HWC just says the lines themselves mean emerging traffic should give way to traffic on the major road. Know your traffic signs gives no further information. Given there's no prohibition for crossing unbroken lines irrespective of the direction of travel, I'd be surprised, (and enlightened), if your interpretation was correct.


I must say I would agree with Gareth's interpretation (and comment). After all the lines will fade away with time and in the dark may not be easily seen. A stranger would not know there was no entry to that road as the arrow is out of sight as you approach from the High Street.

Regards
Brian Haddon