Bus controlled traffic lights

StephenW
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Re: Bus controlled traffic lights

Postby StephenW » 22 Mar 2019, 10:12am

Vorpal wrote:But that is a traffic flow improvement that favours buses, rather than priority.


Ah OK. I think I see what you mean. But it is still potentially a good thing to have, yes?

thirdcrank
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Re: Bus controlled traffic lights

Postby thirdcrank » 22 Mar 2019, 10:25am

IMO, an underlying problem in this country is that both elected councillors and highwaymen AKA appointed officials tend to see maximisation of motor traffic capacity as the priority. This often means that provision for cyclists and buses is aimed at getting them out of the road. eg bus lanes which often end just before traffic lights. The idea that public transport and cycling may be a better use of existing road space is anathema to people trained and socialised to prioritise capacity for motor traffic. Anybody who has been to any sort of consultation will be familiar with the bleats about cycle-friendly infrastructure etc being ok in the diagrams but there's insufficient space. They often struggle with the idea that space needs to be taken from motor vehicles. I'm not saying this is universal, just widespread.

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mjr
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Re: Bus controlled traffic lights

Postby mjr » 22 Mar 2019, 11:32am

StephenW wrote:
Vorpal wrote:But that is a traffic flow improvement that favours buses, rather than priority.


Ah OK. I think I see what you mean. But it is still potentially a good thing to have, yes?

Only when the bus routes aren't the motorists' desire lines, else you still reward the single-occupancy private motorists travelling at a density of 1 person per 48 sq.m (typical car size plus stopping distance @20mph) over bus passengers travelling at a density of 1 person per 3 sq.m (Optare Tempo low-density layout no standing plus stopping distance @20mph) because the motorists will make fewer intermediate stops.

Bus lanes through junctions (fairly old French example) and bus filters/gates are key parts of public transport infrastructure, but the UK rarely builds them, or UK councils try to charge buses for access to them, and that's part of why buses struggle here.
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Pete Owens
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Re: Bus controlled traffic lights

Postby Pete Owens » 22 Mar 2019, 3:07pm

thirdcrank wrote:IMO, an underlying problem in this country is that both elected councillors and highwaymen AKA appointed officials tend to see maximisation of motor traffic capacity as the priority. This often means that provision for cyclists and buses is aimed at getting them out of the road.

Indeed - almost all cycle paths fall into this category - as do bus lay-bys at bus stops. The sole purpose of which is to prevent slow cyclists or stopped buses interfering with the flow of motor traffic.

However:
eg bus lanes which often end just before traffic lights.

does not.

It is neither useful in terms of priority nor desirable in terms of safety to take bus lanes all the way to junctions.

In terms of safety it is important for vehicles to approach the junction in the correct lane for the direction they are heading. Any left turning vehicles need to approach in the left hand lane - otherwise you end up with streams of traffic crossing each other though the junction inevitably resulting in crashes.

In terms of buses making progress it is not in their interest to cause delays to other traffic, just to be able to overtake the existing queues. The area immediately approaching a set of lights should be thought of as a reservoir rather than a queue. The vehicles here are not being held up by other traffic, but will proceed through the junction at the next green stage. It is therefore important that the bus lane reaches just far enough to deliver them into the resevoir. And it is here that signal synchronisation can play a small part. When the bus arrives at the stop before the the junction you can extend the red stage while the bus is stopped and make the lights change just as the bus is entering the resevoir. This is complementary to the bus lane, not an alternative. It is only useful if there is another bus lane beyond the junction.

If you take the bus lane all the way to the lights you are reducing the capacity of the junction by 50%. And while probably for most of us contributing to this forum this is of-itself a desirable end, it is counter-productive in terms of keeping buses moving. As soon as vehicles start arriving at a junction at a higher rate than that junction capacity then a queue will start to form. This is no problem so long as the queue is shorter than the bus lane, but halving the capacity will mean the queue will build up very rapidly. As soon as it extends beyond the start of the bus lane then the buses will get delayed by the congestion caused by the bus lane.

Bmblbzzz
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Re: Bus controlled traffic lights

Postby Bmblbzzz » 22 Mar 2019, 3:11pm

Yep, making the bus quicker than it used to be is good, but not as good as making the bus quicker relative to the car. If you can make the bus quicker than the car, bingo!

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mjr
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Re: Bus controlled traffic lights

Postby mjr » 22 Mar 2019, 3:33pm

Pete Owens wrote:It is neither useful in terms of priority nor desirable in terms of safety to take bus lanes all the way to junctions.

In terms of safety it is important for vehicles to approach the junction in the correct lane for the direction they are heading. Any left turning vehicles need to approach in the left hand lane - otherwise you end up with streams of traffic crossing each other though the junction inevitably resulting in crashes.

Far from being inevitable, you simply avoid it by not allowing the left-turn phase green until after the buses have got through.

Pete Owens wrote:In terms of buses making progress it is not in their interest to cause delays to other traffic, just to be able to overtake the existing queues.

Surely it's in the interests of bus transport to be as much faster as possible than the other traffic, in order to incentivise use?

Pete Owens wrote:If you take the bus lane all the way to the lights you are reducing the capacity of the junction by 50%.

How do you work out 50%? I feel like there must be a shedload of assumptions about numbers of lanes, stages and phases there to reach that high a figure.

Pete Owens wrote:And while probably for most of us contributing to this forum this is of-itself a desirable end, it is counter-productive in terms of keeping buses moving. As soon as vehicles start arriving at a junction at a higher rate than that junction capacity then a queue will start to form. This is no problem so long as the queue is shorter than the bus lane, but halving the capacity will mean the queue will build up very rapidly. As soon as it extends beyond the start of the bus lane then the buses will get delayed by the congestion caused by the bus lane.

But the bus lanes should be continuous back beyond the start of the congestion, which also makes them more useful for the cyclists who are willing to use them.

Stuff like the quoted post has crossed over from vehicular cycling advocacy to simplistic vehicle advocacy that has swallowed a load of motoring lobby arguments against things like bus lanes, filters and 20mph IMO.
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Bmblbzzz
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Re: Bus controlled traffic lights

Postby Bmblbzzz » 22 Mar 2019, 4:21pm

mjr wrote:
Pete Owens wrote:It is neither useful in terms of priority nor desirable in terms of safety to take bus lanes all the way to junctions.

In terms of safety it is important for vehicles to approach the junction in the correct lane for the direction they are heading. Any left turning vehicles need to approach in the left hand lane - otherwise you end up with streams of traffic crossing each other though the junction inevitably resulting in crashes.

Far from being inevitable, you simply avoid it by not allowing the left-turn phase green until after the buses have got through.

What about other vehicles in the bus lane? Taxis, motorcycles, and of course pedal cycles, might be others too in some places. And what about junctions without traffic lights? Either the bus lane becomes a left-turn lane just before every side road and then starts again, or it needs to be continuous and turning traffic has to give way to traffic in the bus lane. The first is probably safer, especially for cyclists and motorcyclists, the second is probably better in terms of bus priority. If the lane is goes right up to the line at junctions with signals, then specific bus-lane lights could be used to give buses (and cyclists etc) priority over other traffic lanes; but this will depend on phasing, of course, and could equally be used to give other vehicles priority.

wjhall
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Re: Bus controlled traffic lights

Postby wjhall » 22 Mar 2019, 5:13pm

As Pete Owen has pointed out the object is to get the bus running to schedule, preferably at 'line speed' not to give it priority in the abstract. In principle average bus speeds will be higher than the average of the general traffic flow, which could also be raised on the bus route. This seems to have happened in the Melbourne study (1) of fairly aggressive tram priority in shared lanes, the reason being that most of the time trams were running to schedule so did not need or gain from priority. Unfortunately although they give average journey time changes for tram and general traffic, they do not tell us what the effect on tram punctuality was, which would be the aim of a system running to a timetable, nor do they comment on whether it would have been possible to accelerate the tram schedule. The possible schedule may be limited by acceptable speeds and accelerations.

(3) Bus & tram priority in Melbourne – conference paper
http://www.jctconsultancy.co.uk/Symposi ... tralia.pdf

StephenW
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Re: Bus controlled traffic lights

Postby StephenW » 24 Mar 2019, 6:50pm

Bmblbzzz wrote:What about other vehicles in the bus lane? Taxis, motorcycles, and of course pedal cycles, might be others too in some places. And what about junctions without traffic lights? Either the bus lane becomes a left-turn lane just before every side road and then starts again, or it needs to be continuous and turning traffic has to give way to traffic in the bus lane.


What about bus lanes in the middle of the road, rather than at the kerbside? This avoids confict between left-turning cars and buses going straight on. At junctions without traffic lights, all right turns would be forbidden. Every so often there would be a roundabout, in order to let motorists make the necessary u-turns, due to not being able to make a right turn. At the roundabout, the bus lane would go directly through the middle of the roundabout, with part-time signals stopping traffic circulating the roundabout, in order to allow the bus to do this.

It would be similar to this roundabout, but with buses rather than trams:

https://www.google.com/maps/@52.374679, ... !1e3?hl=en
https://bicycledutch.wordpress.com/2013 ... oundabout/

I can think of some other benefits of this layout:
-Cycle path crossings of side roads are safer, due to no right-turning motor traffic. This may make bi-direction paths possible in locations where they would not otherwise be possible (if desired)
-Express buses would be able to easily overtake slow buses which stop at every stop.
-No conflict between cycles and bus passengers inadvertently stepping into the cycle path at bus stops. Bus stops would be at islands, accessed either by zebra crossings or pelican, as appropriate.
-Possibility to give advantage to cycles by allowing right turns where they are forbidden for cars.
-Possibility to make buses running early wait at lights, whilst those on time or late do not have to wait (as mentioned in previous link).

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Re: Bus controlled traffic lights

Postby Bmblbzzz » 24 Mar 2019, 7:04pm

https://goo.gl/maps/Koc12fN2Uh12
This offside bus lane now extends far further up the M32. I suspect it's due to this that the bus won the Bristol Post's recent commuter challenge from Parkway station to the centre. Not very easy for passengers to get on and off though (especially to wait in the middle).

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mjr
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Re: Bus controlled traffic lights

Postby mjr » 24 Mar 2019, 7:47pm

StephenW wrote:What about bus lanes in the middle of the road, rather than at the kerbside?

It doesn't move other motor traffic away from the kerb to give an immediate drop at roadside pollution measurement stations, so won't happen often under the current regime.
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Re: Bus controlled traffic lights

Postby MikeF » 24 Mar 2019, 11:47pm

Guided bus lane here and further along. Guided buses have there own set of lights
Bus controlled lights Motor traffic is held to allow the bus to pass.
Left hand turn has bus detector. Therefore bus might be held for a short time while lights change.
Non guided buses can't use the bus lane.
Shared path for cyclists is appalling however. :evil:
"It takes a genius to spot the obvious" - my old physics master

Pete Owens
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Re: Bus controlled traffic lights

Postby Pete Owens » 25 Mar 2019, 10:01am

StephenW wrote:
What about bus lanes in the middle of the road, rather than at the kerbside?


Would make getting on and off the bus a bit exciting.

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Re: Bus controlled traffic lights

Postby Pete Owens » 25 Mar 2019, 10:24am

Bmblbzzz wrote:And what about junctions without traffic lights? Either the bus lane becomes a left-turn lane just before every side road and then starts again, or it needs to be continuous and turning traffic has to give way to traffic in the bus lane. The first is probably safer, especially for cyclists and motorcyclists, the second is probably better in terms of bus priority.


Bus lanes should be broken on the approach to junctions:
https://www.google.com/maps/@53.3844975,-2.5866998,3a,60y,275.44h,84.16t/data=!3m6!1e1!3m4!1sqcebR2rvrT596tj8MNPeWA!2e0!7i13312!8i6656
This enables drivers to get into the correct lane before making the turn.

It makes no difference in terms of bus priority. It is the queuing traffic it needs to get past - any vehicle using the lane to turn left will only be there for a second or two, so not actually delaying the bus at all.

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Re: Bus controlled traffic lights

Postby Bmblbzzz » 25 Mar 2019, 10:30am

Where it's a turn into a minor road, like that, it probably doesn't hold up the bus. Where it's a junction with give way, lights, or roundabout, then it definitely can do. But continuing the bus lane right up to the line can bring other problems.