Centre turning lanes on major roads

lintdrummer

Don't know how to describe this properly but I'll give it a go...

I lived in Spain for a while and I noticed a great feature on their roads. On most major roads, if you approach that road from a T Junction there is a turning lane in the centre of the main road to allow traffic to join the road with more ease.
This means that if you need to cross the road to join it, rather than waiting for a gap in traffic on both sides, you can move to the middle lane when a gap on your side emerges, then join the lane on the far side once a gap there becomes available.

To give a practical example, let's take the N4 between Edgeworthstown and Longford. You are trying to join the N4 at a T junction from the south and you want to turn right towards Edgeworthstown. You have to cross the road to do this. If there was a centre lane you could turn right onto this when there is a gap in westbound traffic. You then only have to wait for a gap in the traffic eastbound to continue your journey.

Seems like a very sensible and safe solution on busy national roads, could it be implemented here?

I'm attaching a crude MS Paint drawing to illustrate the idea.

H3llR4iser

I obviously assume you flipped the design in the chart to adapt to driving on the left.

The way I see it, it's a double edged sword - what it will do is slow down traffic on the main road; in your picture's case, cars coming from the left end.

The reason is simple - cars coming from the bottom road will join the middle lane, then from there look to merge into the traffic coming from the left; This will cause drivers coming from that direction to slow down, brake and generally have to work around the merging traffic, which will have a rippling effect behind them.

Think motorways - at peak times, most of the slowdowns are around entry slip roads, where vehicles try to merge the existing flow.

The beneficial effect, however, is that it would ease congestion from the road at the bottom.

biko

They are very popular in US

H3llR4iser

The way I understood it, they're the other way around - they're not for turning FROM the main road into the side, there are plenty of these in Ireland, they seem to be sort of an "acceleration lane" to merge... I will admit to being in Spain but never noticing a single one of these.

Isambard

if you have a problem joining a road by turning right, then turn left and turn right at the first opportunity and double back.

lintdrummer

H3llR4iser wrote: »

I obviously assume you flipped the design in the chart to adapt to driving on the left.

The way I see it, it's a double edged sword - what it will do is slow down traffic on the main road; in your picture's case, cars coming from the left end.

The reason is simple - cars coming from the bottom road will join the middle lane, then from there look to merge into the traffic coming from the left; This will cause drivers coming from that direction to slow down, brake and generally have to work around the merging traffic, which will have a rippling effect behind them.

Think motorways - at peak times, most of the slowdowns are around entry slip roads, where vehicles try to merge the existing flow.

The beneficial effect, however, is that it would ease congestion from the road at the bottom.

Yes, I drew the design for an Irish perspective. I don't agree that it will slow down traffic coming from the left. As it is, people have to take the first opportunity that arises on both sides to get across the road and are more likely to leave a smaller gap to traffic already on the road.

biko wrote: »

They are very popular in US

Yes, I've seen them in the US but they are used to turn off a main road rather than onto it, as the picture you attached proves. The arrow for traffic joining from the left doesn't indicate use of the middle lane. They have this in the US because they often have two or three lane carriageways in urban areas.

H3llR4iser wrote: »

The way I understood it, they're the other way around - they're not for turning FROM the main road into the side, there are plenty of these in Ireland, they seem to be sort of an "acceleration lane" to merge... I will admit to being in Spain but never noticing a single one of these.

You're describing them exactly as I did, they are designed for joining the main road, not leaving it.

Isambard wrote: »

if you have a problem joining a road by turning right, then turn left and turn right at the first opportunity and double back.

That's not ideal is it, I doubt too many actually do that even if it makes sense.

unhappyBB

I've often wondered why we don't have these too, it just seems like common sense.
We already have short middle lanes to exit a road to the right, why not extend these a bit so cars joining from the right can get lined up to merge safely.

Isambard

lintdrummer wrote: »

That's not ideal is it, I doubt too many actually do that even if it makes sense.

no it's not ideal but crossing two lanes with fast moving traffic can be daunting and a nervous driver hesitating for weeks can be a real nuisance.