Causes of Congestion in the Greater Bristol Area: hint: not 20 mph zones

What has made congestion in and around Bristol worse —for those people driving or sitting in buses?

Some people are saying it's common sense that it's the 20 mph limits, and that common sense beats data. No: thinking beats common sense.

we can argue about whether @georgeferguson_x did things to make traffic worse;

RPZs didn't; they add more passing places to the narrow roads, and if they discourage people from driving in, could reduced traffic levels.

20 mph a factor? Not given average weekday traffic speed. (Source: Waze)



One key point is that if the average speed in a road is 2-7 mph, as Stapleton Road is enjoying, then 20 mph is an unrealised dream. It's not the problem. Question is: what's causing that delay?

The main factor is the number of people choosing to drive. Evidence of this comes from looking at the M4 heading away from Bristol, which is going at 12 mph.

By choosing an away-from-city route we can avoid blaming metrobus related roadworks or buildup from urban congestion. There's none of : cyclists, bus stop buildouts, traffic lights or 20 mph to blame rather than accept the root cause of the traffic jam is the decision of you and others to get in the car that morning..



It's people driving places. Which may be correlated with population growth, and the growth of north fringe sprawl housing and offices. North Lockleaze, or, as it pretends to be, Chiswick Village? New. Those fields north of the A4174 by Emerson's Green? Houses you get to see from the M4. That's a change: more suburban housing, more people driving around the city.

Secondary factors to motor traffic in town:  junctions, buses stopping, vehicles turning right, cars parked where they shouldn't. All amplified by traffic volume: bigger queues, longer waits, more turning vehicles, more people "just parking for a minute" in a bus lane, so forcing the bus to try and pull out and increasing overall unhappiness.

Traffic lights? They have a worse (but fairer) throughput compared roundabouts; see Modeling Roundabout Traffic Flow as a Dynamic Fluid System (skip the pictures and look at the pics on P8-11, knowing that "flux" means "number of vehicles arriving per second"). Essentially, all of junctions overload, but two-lane roundabouts get the most through.However that paper assumes that you can get off the roundabout, which as we know at peak hours (Hello Bearpit! Hello St Pauls Roundabout!) doesn't hold. Furthermore by modelling traffic as an incompressible fluid, they miss out on the game-theoretic aspects of the problem, as in: why you'd pull out in front of other vehicles, even if you know it will block others.

Because one problem roundabouts and traffic lights both have is people blocking junctions, so stopping cross traffic getting through. If anyone has evidence of yellow-hash do-not-block zones ever being enforced, we'd love to see it. We lack that evidence. What we do believe is that it would reduce junction deadlocks and so boost cross traffic. Again, evidence would be good. Perhaps the council could run an experiment —like enforcing the law for a week.

Fast moving cyclists? Nope. They just go past the queues and have an average speed above cars at peak hours. This clearly upsets some people who resent the fact that they have to drive a Fiesta 1.1L up the A38. We would hate driving a Fiesta 1.1L too, even on an empty road.

Cyclists at under 12 mph? No data. They are easy to pass when there is no oncoming traffic, so as the overall traffic volume increases, get harder to pass. Having bus lanes and functional (i.e. not blocked by parked cars) bike lanes, lanes considered safe enough by cyclists that they use them would eliminate that problem. And, if parking spaces taken away for them, reduce justification for driving in.

Oncoming traffic? This is a problem in much of the inner city: there isn't space to get through down a road in the presence of oncoming vehicles. As well as traffic volumes, we have to consider whether the rise of the Urban SUV amplifies the problem. Not only does that oncoming Volvo XC 90 on the school run take up more space, the VW Touran parked alongside the Audi Q6 means that there is less open road to play with anyhow.

Roadworks? We know about those, especially: in the centre, on the M32, along the A4174, the A370 and by Cumberland Basin. Hopefully they will be transient, as in "fixed before 2020"



One thing is for inevitable: the cost of delays caused by these roadworks won't have been included in their already broken cost model.

When that Metrobus work is finished, will the problems go away? Not without some fundamental change in how people get into the city —which means that you need a compelling story from places like Yate, from Portishead, and the other dormitory towns. A railway from Portishead here is potentially compelling, because you get a direct line to Templemeads without traffic delays.  It's a shame that central government beliefs (trains bad, BRT viable) and local government issues (naive optimism) have caused a focus on FirstBus as a solution.

Will Metrobus be compelling for those actually in its catchment area? We have no idea whatsoever. Which gives us something in common with the metrobus team.

Anyway, to close: for anyone saying "it's the 20 mph zones", or "its the traffic lights", we say "explain how the M4 moves at 12 mph on a weekday morning?"

Stoke's Croft back to normal

We are pleased to announce that after the intervention of the new city regime, parking on Stokes croft is back to normal -only the bike lane is occupied, here by a 4x4 K215SHR, and a shopping trolley. When will something be done about the shopping trollies?

Meanwhile, over in our local legacy printed press, Bristol is now the worst city (ignoring London) for traffic, according to a new survey.

This survey " examined demand measures – the population density, wealth of the population and the office stock – and supply measures – road density, the transport budget and rail provision.". The result is a list of cities, Cardiff at #1, Glasgow at #3, Edinburgh at #5 and Bristol at the bottom.

Road density = road area divided by the population. Is that really a good metric for good city transport? The amount of space dedicated to gettting between places? No wonder in this list Glagsow comes in at #3 -their M77 motorway to Kilmarnock cuts straight through PollokEstate, the city's park; the M74 tore up the countryside near Uddingston, the M8 cuts the city apart and allows you to get from your Loch-Lomond holiday cottage back to London without any risk of encountering the locals in the much-feared Gorbals. More strategically, the M8 lets you get your non-conventional armaments to the Faslane submarine base from your factory in the South East, without getting lost the Gorbals.

Public transport is more interesting. Edinburgh, in at #5, is a lovely city to cycle round. But you aren't going to drive round as it's had residents parking for 25+ years, making up for it with a council-run bus service -Lothian Buses- that works. Low cost; day buses; night buses. You name it. And there's good mountain biking. It even gets its tram service, even though they voted against congestion, as the Scottish parliament is funding it -no need to go through the TIF bidding process.

The key local comparison has to be with Cardiff, as that is the closest city; apparently it is "better". Whoever did that survey has clearly not included the welsh valleys, with a mixture of rural deprivation since the end of the coal mines is mixed with commuter jams as people drive into Cardiff from ex-coal-towns like Merthyr Tydfil. Cardiff has its problems too, and to pretend that all is well there but not in Bristol is to miss the point, a point that Virgin's survey in 2007
didn't.

So why is the survey so wrong? Well, who did it? Property developers. Bristol has a very high population density. Saying Bristol is at fault for not having enough km of road per resident is wrong -a better measure would be square metres of road per square kilometre of city, measuring the percentage of the city's area that was dedicated to traffic -and adding the area (including pavements) dedicated to parking. Once you do that, given our city's population density, the figures won't look so bad.

But if you are a property developer trying to sell middle-of-nowhere city suburbs (e.g. the Tailspin estate by the MOD), you don't want to push inner city car-free living. You know that the locals aren't going to walk to Sainsbury's then push a trolley full of shopping back, let alone walk to Filton Avenue and wait 45 minutes for a 73 bus to the centre. No, for suburbs to work, you need cars or some functional public transport alternatives, which is exactly what this report is criticising the city for lacking. This feeds well into the EP's the-city-is-at-war-with-cars theme we know and celebrate ourselves. Equally importantly for the developers, you want to get your name in the papers -and you don't do that by some press release that the local papers don't agree with -which again means complaints about traffic are pretty much mandatory.

1. Leicester declared third worst city.
2. Birmingham named worst city for commuters in 2008
3. Cardiff named worst city to drive in by Virgin Insurance.

We should make up some of these ourselves.

Oceania has always been at war with Eastasia

News from the Ministry of Truth (Bristol Section)

This site welcomes contributions from all participants in the Bristol Travel area, and today we are pleased to have a contribution from the Bristol Council section of the Ministry of Truth, here to bring us some current news.

1. Oceania has always been at war with Eastasia. Anyone who believes the enemy was at one time Eurasia is mistaken and should report themselves to their nearest Ministry of Truth office for correctional measures. It is only by struggling with our Eurasian allies that victory over the Eastasian animals will be achieved!
2. The chocolate ration will be increased from 60g/week to 40g/week!
3. The single pedestrian crossing on the Princes Street Bridge will be widened, along with a lane for bicycles to get past. This reduction of car traffic from two lanes to one lane is necessary part of the Bristol Cycling City Initiative.

Anyone who believes that there are in fact two narrow pedestrian footpaths on this bridge is a thought criminal.

Anyone who proclaims differently in public is guilty of spreading malicious propaganda against the city.

Anyone who claims that the proposed Princes Street changes are necessary to permit Bus Rapid Transit bendy-buses to get over the bridge without spending money on new bridges is repeating untruths.

Anyone who believes that the announcement was phrased the way it was to put the blame on cyclists or to redirect Cycle City funding towards BRT development is misguided. Please report such subversives to the truth maintenance committee at the council.

Thank you for your co-operation. Ministry of Truth (Bristol Section)

Muller Road: 20K cars/day

One of the interesting facts to come out of Josh Hart's Bristol street study is that 20,000 cars per day go along it. Morning and evening it is congested going to and from the M32; cars coming from Lockleaze cut through garage-alleys to spend less time stuck at the Shaldon Road junction

And so get into the queue leading up to the M32 that much faster.


It's a tough road to walk or cycle across; you need to wait at the lights and factor in to the light schedule the fact that cars coming off the m-way are slow to react to red lights. In the Bristol Cycling Campaign, the Muller Road/Shaldon Road junction is viewed as positively lethal, the fact that 'safe route to school' improvements made it even more dangerous should have been a warning sign about threat that a "cycle city" bid could present.

One thing that Josh's study didn't do is ask where do these cars go to? Where are they coming from? Assuming they are coming into the city on the M32, not using the ring road exit but pulling off before getting stuck in the traffic jams by the M32 junctions further into town, these cars are heading to North West bristol, but not the North Fringe. So where do they go?