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So, you acknowledge your earlier claim that delays on both sides of the Hogarth Roundabout are down from 2019 to 2023 is not a 'simple fact' but rather inaccurate. As I understand what you are saying, if you take delays per km on both sides of the roundabout, make an adjustment for the distances you could argue that it is possible that the total delay from the junction with British Grove to Chiswick Roundabout might be down slightly in the context of significantly increased congestion on other sections of the A4. Even setting aside that these appear to be figures for the whole day rather than peak hours so don't necessarily give us the true picture, you are having to make them work very hard to fit your narrative. Let's just assume that this pattern of reduced delays between Hogarth Roundabout and Chiswick Roundabout is followed during peak hours, isn't it worth reflecting why this might be happening? After all, it does seem strange that congestion is increasing everywhere else but this one small section. What explanation do you have for this other than the obvious one i.e. that TfL change the phases on the lights at SCR and Hogarth Roundabout to make traffic run more quickly on this stretch to avoid tailbacks exacerbating congestion in each direction.  You can see this in action right now (map below from 8.15 this morning) — the A4 is running smoothly in the morning rush hour but there are long queues back down to Chiswick Bridge along the A316 and up to Chiswick High Road from Sutton Court Road. So it may be on a 1.6km part of the A4 there has been a slight reduction in delays but this is coming at the cost of heavy congestion elsewhere in Chiswick.



Jeremy Parkinson ● 51d

I am very sorry if I misrepresented you in anyway. That wasn't my intention.Some might contest your view that eastbound delays through Chiswick are down as Chiswick doesn't end at Hogarth Roundabout but that's by-the-by.We are at risk of drifting away from the whole point of this discussion which is the question of whether the widening of the A4 could be partly being considered to alleviate current and expected congestion on the A4.Specifically the plans are focused on the westbound carriageway so it would really be more useful to have the westbound data. However, I think the apparent contradiction of traffic speeding up a bit eastbound from Chiswick Roundabout to Hogarth Roundabout and slowing down east of there may be partly explicable by increasing queues westbound.Traffic lights around Hogarth Roundabout and Sutton Court Road are managed dynamically. If westbound queues are forming TfL will shorten the phases at these two junctions to reduce westbound tailbacks but this will also speed up eastbound flows between Chiswick Roundabout and Hogarth Roundabout concentrating the delays further east.The claim that traffic is being reduced 'through Chiswick' ignores the resulting queues that develop on the A316 Burlington Lane, Chiswick Lane and Sutton Court Road as a result.Delays westbound on the A4 out to Chiswick Roundabout have increased significantly from 2019 to 2023 and therefore it must be assumed that the light phasing at these junctions has been consistently less favourable to local traffic crossing the A4. This chimes with what many people have been saying about queues on SCR, the A316 and Chiswick Lane. A rise in fuel duty in the budget may lessen this trend slightly in the short term but, going forward, there appear to be lots of factors that will increase usage of the A4 and few that will reduce it, so I remain unconvinced this problem isn't going to get progressively worse.

Jeremy Parkinson ● 56d

"I'm stating that INRIX reports a reduced delay on the A4 through Chiswick in 2023 compared to 2019"When you say "through Chiswick" you are being misleading. You are quoting figures from INRIX that you have discovered which show higher average speeds between Hogarth Roundabout and Chiswick Roundabout during the course of the whole day. The problem for peak hour westbound journeys is the tailbacks from Hogarth Roundabout back towards Piccadilly.INRIX in its annual report choses not to focus on one narrow section but a longer length of the A4 and the report shows categorically that congestion has increased significantly from the west end to Chiswick Roundabout from 2019 to 2023 with wait times increasing from 10 to 14 minutes at peak hours.You are right however, that the average number of vehicles fell between 2019 and 2023. I can't give a categorical explanation as to why this might be but possible reasons are that the DfT traffic data is for a daily average and it may be that peak hour vehicle movements are up or a rise in HGV traffic and an increase in the size of cars since 2019 has made congestion occur more quickly with the same number of vehicles.The fact is that without speculating or arguing we know that congestion on the A4 is getting worse. I really don't understand why you continue to dispute the unambiguous conclusion of the traffic analysis experts who have produced a report on this as well as what surely must be the evidence of your own eyes.

Jeremy Parkinson ● 61d

Michael, the 'so what' here is the impact that A4 congestion has on Chiswick. The phasing of lights is dynamically managed and when queues build up there are shorter phases for the roads crossing the A4 in this case the A316 and Sutton Court Road. Looking at traffic conditions on Google Maps as I write there is queueing down past Edensor Road on the A316 right now. When the phase on SCR is shortened, traffic queues reach up to Heathfield Terrace and have a knock on effect on the High Road. If A4 usage is increasing the number of 'traffic events' in the centre of Chiswick will rise.You are right that congestion will discourage some journeys and some will 'evaporate' but others will be displaced leading to more congestion across Chiswick.It is also correct to assume that the ultimate resolution to this problem has to involve some sort of pay per mile system probably with a premium rate for use of the busiest roads at peak times. However, ULEZ has probably put the implementation of this back by up to a decade because of the political fallout. The new system has to be carefully designed to not be as regressive as ULEZ otherwise it will not be possible to persuade people it is necessary.Tom, I'm not sure how you can say that congestion on the A4 has not increased since pre-Covid when a comparison of the INRIX reports from 2019 and 2023 shows that this is exactly what has happened. The average peak time delay westbound on the road through Chiswick has risen from 10 to 14 minutes resulting in it being ranked as the third most congested in the UK.That you have managed to dig out a stat that shows average speeds across the whole day may have increased on a section of this road doesn't negate INRIX's conclusion. As I write the queue off the A4 is stretching back up Chiswick Lane. I don't think you would get a pleasant response if you told anyone sitting in traffic there that the congestion was imaginary.

Jeremy Parkinson ● 63d

I haven't been able to find the INRIX data you refer to but I'm not querying their accuracy.The numbers in the INRIX annual reports I cited are for the A4 eastbound from the west end to Chiswick Roundabout, a much longer stretch which show a significant increase in peak time delays from 2019-2023.It is entirely possible that average speeds could have increased between Hogarth Roundabout and Chiswick Roundabout during this period. This would be achieved by changing the phasing at the Sutton Court Road junction and using this road, including E3 bus users can tell you the green phase going north to south can be cut to a few seconds leading to tailbacks into the centre of Chiswick.The average speed achievable on the clear section of the road to the west of Hogarth Roundabout may have increased but, in the last four years, it has not done so sufficiently to reduce the journey time along the broader stretch of the A4 we are looking at.On correlations, assuming you agree that there would be a positive correlation between Heathrow airport arrivals and traffic on the A4 and the significant increase in population density taking place on the A4 corridor will also tend to boost demand to use the road, would you not accept that, all other things being equal, congestion will rise?For the past decade or so there has been a number of factors with a negative correlation with A4 use eg regulatory - ULEZ and the Congestion Charge, social, infrastructural - improved public transport such as the Elizabeth line. The effect of these has ended or may be even reversing and I can't see other influences that would tend to suppress the number of vehicles on this road.I'll ask again, why should we not be concerned about increasing congestion on the A4 in Chiswick? It already has the third most congestion in the UK and therefore probably Europe and the problem has got significant worse from 2019-23. Perhaps this time you could answer without trying to bog the argument down in semantics, not come up with an out of context piece of data which doesn't actually prove anything and refrain from calling me a slippery dunce. I am genuinely interested in what you have to say but your refusal to address this simple and paramount question concerns me.

Jeremy Parkinson ● 64d

"You're just being very slippery here, Jeremy. Since 2000 passengers at Heathrow are up 25% and traffic on the A4 at Hogarth roundabout is down 10%. There's no error in those numbers, is there?"No there isn't but I am perplexed you don't seem to understand the difference between a positive correlation and an exact correlation."I haven't said anything about congestion - you're just making that up!"Am I not wrong to have concluded that in the past, for instance regarding Chiswick High Road and the A316 that you have argued that a reduced number of vehicles recorded as travelling along a road proves that the congestion that people have observed isn't happening? "But as for congestion on the A4 through Chiswick is concerned, maybe you need to look at the actual INRIX figures for the stretch of the A4 through Chiswick! In 2019 the delay was 97s and in 2023 62 s. For the third time in one thread, you've failed to actually look at the data before sharing your opinion of what you think the data is! Other people can judge if that makes you a dunce you yourself suggest."You may have access to more detailed figures from INRIX than the rest of us but I am looking at what it publishes at the time of its annual traffic report.In 2019 it stated that the average peak time delay in traffic approaching Chiswick on the A4 was 10 minutes:https://inrix.com/press-releases/2019-traffic-scorecard-uk/#:~:text=The%20findings%20show%2C%20on%20average,hours%20per%20year%20to%20congestionBy 2023 the same report was saying that the delays on the same stretch of road had risen to 14 minutes making it the UK's third most congested road with the eastbound carriageway second. https://inrix.com/press-releases/2023-global-traffic-scorecard-uk/The DfT numbers do show that the number of vehicles on this part of the A4 is down from 2019 to 2023 so we have apparently fewer vehicles moving more slowly. It would be interesting to hear how you account for this but surely the increase in HGVs has to be a factor along with ULEZ discouraging more off peak private car journeys.The broad overview remains that we have UK's third most congested road going through our area with every indication of increased demand for usage ahead with no mitigations planned. I'm concerned about this and the impact it may have on our community going forward. Perhaps you could explain in simple terms in words that a dunce like me can understand, why I don't need to be?

Jeremy Parkinson ● 65d

We all make mistakes but perhaps its a lesson that observation does provide a sanity check for conclusions based on purely looking at numbers.Tom also seems to have somehow got it into his head that I am arguing that there is a total correlation between Heathrow Passenger arrivals and traffic on the A4. I hope it is obvious to others who have read what I have posted that isn't what I am saying.2018 and 2019 were the two peak years for Heathrow passenger throughput. 2017 and 2019 were the peak years for the number of vehicles using the A4 at a point just east of Hogarth roundabout with 2018 marginally behind 2017.There are obviously a lot of factors that influence the number of vehicles using the A4 in addition to Heathrow and in recent years these would include ULEZ, the congestion charge, the opening of the Elizabeth line, drop off charges at the airport and the level of congestion. These mean there won't be a perfect correlation between Heathrow arrivals and A4 traffic but in 2024 I can't think of any factor that is likely to have more influence that Heathrow passenger numbers. If you take the monthly numbers so far (up to September) and assume no growth for the remainder of the year compared to 2023, the airport will smash its previous record. For the A4 to reach a new high it would have to see an increase of around 15% in vehicles which may not happen as it would be greater than the increase in Heathrow's numbers but there doesn't seem to be any factor mitigating against traffic growth at the moment. I asked earlier what would offset other trends such as airport expansion and the huge number of housing starts in the A4 corridor and the only answer I got was the possibility of a signalling upgrade for the Piccadilly line.It would be helpful that, rather than coming up with irrelevant quibbles about data, those who disagree with what I am suggesting would explain why we don't need to worry about continued traffic growth on the A4 and why TfL isn't worried if they don't believe the Hogarth Roundabout plan was primarily about relieving congestion.

Jeremy Parkinson ● 70d

"The relevance of historical data is that M4 traffic volumes were even higher prior to 2010 than they were in 2019, let alone now."I'd admit past data is relevant to an extent but not predictive. I don't know what data point you are looking at but the one I am using is Site number: 46121 which is just to the east of Hogarth Roundabout. This shows that with a few outliers, the number of vehicles passing this point on a daily basis is between around 85,000 and 110,000.It is not correct to say that there were higher occurrences at the beginning of the century than we have seen in recent years. The peak was 2018 followed by 2019 which also happen to be the peak years for Heathrow passenger numbers. The monthly Heathrow numbers indicate that the 2018 record year will be substantially exceeded in 2024. Past data suggests that this will be accompanied by a similar increase in traffic on the A4."HGVs only make up about 3% of vehicles on the M4, the overwhelming majority are cars, so even if HGV volumes doubled, traffic would still be less than it was in 2019 and a lot less than it was in the 00s."There is a confusion here between 'traffic' and the number of vehicles on the road. HGVs take up much more road space and combine that with the significant increase in car size, the same number of vehicles that used the road in the 00s will cause a lot more congestion in 2024.My concern is that if you combine the Heathrow resurgence, with the lessening of the dampening effect of ULEZ as people switch to compliant cars and the significant growth in housing units along this corridor (28,000 in Hounslow borough alone) we will see the number of motor vehicles on the A4 go beyond the historic range.Mark is right that better public transport can help and there may be some forces that create an equilibrium here that prevent vehicle number rising above a certain amount. However, TfL don't seem to believe this which is why they want to widen the A4.

Jeremy Parkinson ● 71d

Given the relative volumes of traffic, the increasing tailbacks on the A316 are likely to be primarily caused by more vehicles using the A4. Heathrow is at record passenger levels and freight is also seeing strong growth.This has resulted in longer tailbacks both ways and TfL seems therefore to have reduced the phase times for roads joining the A4 which means the queues back along the A316 and Chiswick Lane are getting longer.Tom Pike will tell you that the number of vehicle crossings over Chiswick Bridge has fallen since Hammersmith Bridge closed and he is not wrong. He would further claim this is down to 'evaporation' which is probably partly true. Whether through the use of traffic-sensitive SatNavs or just experience, the congestion on the A316 will mean that people will avoid the route. How many cancel their journey and how many are displaced elsewhere we don't know. However, we can see while there are fewer vehicles using the road there is far more congestion. Just talk to a parent of a child at Cavendish school if you doubt this.That's not to say the Hammersmith Bridge closure and, to a lesser extent, the Grove Park access restrictions, don't mean the A316 queues aren't worse than they might otherwise be but I think we would still have them even if the bridge fully opened and the restrictions were scrapped.There doesn't seem to be any prospect of usage of the A4 falling so this problem is only going to get gradually worse so it is understandable that TfL wanted to take measures to deal with it.

Jeremy Parkinson ● 75d