A Public Transport Grid for the M4 Corridor…

In March 2020, I submitted a paper to the South East Wales Transport Commission to consider in their deliberations over the M4.  This essentially is that paper (with a few minor updates and reflections) which draws much from my blog “No new M4… so what instead[i]  from Summer 2019. There is nothing in here that is not either already in the public domain or are my own proposals. It’s not rocket science!

Post Script November 2020, Really pleased to see many of the ideas and concepts set out below, especially the application of the SWML as the backbone of our Public Transport Grid, being at the core of the recommendations of the South East Wales Transport Commission. Its a good read and I applaud the work of the commission


This brief paper sets out the rationale for a major investment in public transport capacity (as a strategic alternative to the M4 Relief Rd) along the M4 Corridor, within & between Cardiff, Newport and onto Bristol, to attract at least 2000 people/hr away from M4 car trips, and to provide  viable public transport options for journeys within Cardiff and Newport.

I have also reflected on the current Covid crisis and potential changes to working and mobility behaviours[ii].  Whilst they will change (not as much as some would like and more than some will want!), it still is evidently clear that our climate change obligations means that we still need much more public transport capacity (given today over 80% of us still commute in cars); as well as needing to change many other aspects of how we live and how our economy functions[iii].

This will require the development of a grid public transport network to connect most of the urban areas of Cardiff and Newport (pop. over 500k) with integrated, regular & frequent services.  The foundation for this grid will be a major upgrade of the SWML Figure 1. Subject to further analysis, these proposals could:

  • Significantly reduce transport-based carbon emissions
  • Reduce peak demand on the M4 by 20-30% allowing it to operate more reliably
  • Provide an alternative to car-based journeys across urban Cardiff & Newport
  • Encourage future development around public transport hubs and corridors
  • Help reduce congestion and improve air quality.

There are though some thorny issues to address if we want to deliver these proposals. 

We need a road user charge to both discourage car use, and to help fund the capital programme implied. More challenging, we need the UK Government to fully devolve rail powers and funding to Welsh Government. Today it  is the UK Government that has responsibility for  maintaining and investing in  the rail network in  Wales  – not Welsh Government (apart from the core valley lines, part of the south Wales Metro, which transferred to WG earlier in 2020).

As I have written and stated previously (including work for WG) UK Governments have, over decades, systematically depreciated Wales Rail network when compared to the rest of the UK network[iv] [v].  I can also assert, quite confidently, that if the Senedd or Welsh Government did not exits there would be no South Wales Metro project; that project is happening despite the lack of enthusiasm from the UK Gov and DfT back in 2011/12/13.

So, we need some mature politics at both ends of the M4 (and mainly the London end) to bring these ambitious M4 corridor public transport proposals to life.

Figure 1 Possible M4 Corridor Public Transport Grid Network


Like most major UK urban motorways, the M4 around Newport suffers (pre-covid) peak time congestion from of the order of 5000 vehicles per hour moving in each direction (carrying perhaps 6000-7000 people). Most congestion results from journeys which are short (10-40km) primarily resulting from commuting from/between Newport, Cardiff and Bristol. The M4 is not unique in that respect as DfT’s own data shows  Figure 2  that such congestion is the norm across the UKs major urban motorways[vi].

Figure 2 DfT 2018, Volume over Capacity in 2015

It is also becoming very clear that building more road space generates more traffic and that many of the costs of car use are external and have not been adequately appraised or recouped over decades  Figure 3 .  Please look at my blog from last year on this[vii], the work of people like Todd Litman[viii] and Jarrett Walker[ix] and even the DfT’s own analysis of induced demand[x].  More alarming, the long-term induced demand impacts are not formally quantified when appraising new road schemes!

This video re freeways in Houston is a good explainer….

Figure 3 External Costs of Car Use, Todd Litman Victoria Transport Policy Institute

I will stress this point, all of us as car users, have effectively been given a discount to drive unimpeded for 50 years.  There are real external costs that have not been levied on this “freedom” which have resulted in sprawl with car based housing and employment sites that generate an even greater demand for road space, damaging our urban realm and impacting air quality.  The executive summary of Transport Costs and Benefits by the Victoria Transport Policy Institute is a good guide[xi].   It’s an unvirtuous cycle we have to reverse.

Specifically, I’d like to draw your attention to one of the major external cost, and something we have become desensitised to. In the UK there are about 5 deaths on average each day (1700 per year!) on the UK’s roads[xii]; this is in addition to 25,000 serious injuries and 160,000 road traffic incidents. There are also significant air quality and health impacts that are only now being fully appreciated[xiii] which leads to perhaps as many as 20,000 premature deaths each year!  If the public transport network did that it would be closed down immediately!

This is on top of the carbon emissions resulting from car use[xiv]  Figure 4. Even with all electric vehicles, the current high usage of cars will still result in massive amount of carbon dioxide being issued into the atmosphere.  I have written[xv] and presented on the subject of cars quite a few times in the last few years, most recently at a Smart Mobility Symposium in Germany[xvi] before the Covid lockdown!

Figure 4  EU CO2 Emissions by Sector

Figure 5 From M Barry presentation to Smart Mobility Symposium Bielefeld Feb 2020

This must, and will, change.

The stark fact is that since the 1950s we have depreciated our public transport infrastructure and over the same period expanded our car-based infrastructure.  If we can secure a sensible and reasonable shift to public transport and active travel, we will find that we have more than enough road space for those that still need or choose to use their cars for particular journeys. When one factors in a better balance of work/home/local post Covid, then the case for new road space diminishes even further. The priority must be investment in public transport capacity not more road space!  The planet needs far fewer cars!

So back to the M4 Corridor

Stats Wales commuting data[xvii] suggests up to 14,000 people from SE Wales commute across to Bristol every day; a significant portion of this will be using the M4. The vast majority have to use cars, given that access to regular rail services to/from Bristol are restricted to only Cardiff Central and Newport.  Along this corridor there is very little option to use any mode other than the car. Intra/inter regional bus services are poor and do not penetrate the urban areas and there is only one primary rail station between the Severn Bridge and Cardiff Central. Disappointingly the M4 Relief Road programme and the enquiry, only assessed small scale and tactical public transport interventions[xviii] and did not note how relatively inaccessible rail services are to the majority of people in Newport and Cardiff.

Figure 6 Population Density Vs Access to Rail Service from Metro Impact Study 2013

The 2013 Metro Impact study identified the highest and most densely populated part of SE Wales with the worst access to rail service as East Cardiff and most of Newport; this understates the issues in Cardiff where the City and Coryton lines offer a suboptimal 2tph service.  In fact, only 24% of Cardiff’s residents will be within 800M of a rail station offering 4tph after the next phase of Metro. Newport is even more poorly served. Again, it is not surprising that people choose to use their cars given this analysis.

What is needed…

To significantly address congestion on the M4 is a need to provide a viable public transport alternative for perhaps 20-30% of the current demand.  It is worth noting that at peak times, broadly, it is 20% of the traffic that causes 100% of congestion. That would suggest taking at least 1000 ~1500 vehicles per hour off the road; or of the order of 1500~2000 people an hour.

To note, in terms of carrying capacity, a fully laden 6 carriage train can carry approximately  500 people, a single set tram-train (as being produced by TfW) can carry 240 people (so nearly 500 in double set), a modern single floor bus ~ 80 people (articulated bus ~150). 

The market for public transport is sufficiently large along this corridor to consider the most optimal solution in respect of long term opex & revex; this lends itself to rail (LR & HR) and segregated bus solutions subject to capital affordability & deliverability. Cardiff, and Newport to a lesser extent, has sufficient size (combined pop. over 500k) and density of urban population[xix] to support segregated transit (LR and/or BRT) which needs a minimum population of ~200k and a density of perhaps 22 pph (people per hectare)[xx].

The current phase of metro (to 2023/4) will deliver major accessibility benefits to Merthyr, RCT & Caerphilly. This, and the M4 relief road decision, increases the importance of future phases in and between Cardiff and Newport and along the M4 corridor from Bridgend to the Severn bridge. Measures to provide more public transport capacity have been explored in recent years (in addition to my 2013 Metro Impact Study[xxi]). These include:

  • Cardiff Council’s Transport White Paper[xxv] (including their Crossrail[xxvi] , Circle as well as major bus and BRT measures), it also set out
    • the major air quality and congestion challenges the city is facing which are an order of magnitude higher than anywhere else in Wales
    • the connectivity challenges impacting the city’s economy and that the city has more LSOA in top 10% WIMD than any other local authority in Wales

  • The Cardiff Capital Region’s work on Metro+ sets out a series of tactical measure to enhance access to the public transport network across the region

  • Both WG and NR have also undertaken studies to explore enhancement to the relief lines and other measures along the M4 corridor; going further back, SEWTA had also set out some proposals for the relief lines.

A Solution for the M4 Corridor

In my view, the M4 corridor needs a grid of high-quality public transport services across the main urban area Figure 1 .  This has to be based around a major upgrade to, and an increase in rail services along, the SWML and Relief Lines with new stations and high-quality interchanges to local services (rail, tram-train and bus). 

This will require more express rail services from west Wales and Swansea to Bristol Temple Meads and London. This backbone of the grid which would then support more local feeder connections using bus, local rail and local tram-train services from across the major urban areas of Newport and Cardiff.  For example (and I won’t go into too much detail here as I have covered a range or potential measures in other blogs, reports and publications):

  • New local all stop commuter services linked to a number of new stations (especially between Bridgend and Severn Tunnel Junction) – for example Magor, Llanwern Cardiff Parkway, Rover Way/Newport Rd, M4 J34, etc

  • In Cardiff & Lower RCT the Cardiff Crossrail[xxvii] & Circle & NW Corridor projects plus further bus and Bus Rapid Transit (BRT) measures will connect a very large number of people to SWML backbone rail services

  • In and around Newport major BRT measures and a future expansion of tram-train services from Caerphilly to Newport will also connect to the SWML.

  • Enhanced frequency and capacity of services on the Maesteg, VoG, Ebbw Valley and Marches lines

  • Addressing bottlenecks on NR’s network impacting these proposals (for example Park/Ebbw Junction and Cardiff West junction)

  • More strategically measure to address the capacity constraint of the two-track mainline between Cardiff and Bridgend. 

  • Much improved Active Travel connection to all our stations

As stated above, collectively, these measures will:

  • Significantly reduce transport-based carbon emissions

  • Reduce peak demand on the M4 by approx. 20% allowing it to operate more reliably

  • Provide an alternative to car-based journeys across urban Cardiff & Newport

  • Encourage future development around public transport hubs and corridors

  • Help reduce congestion and improve air quality.

Capital Estimates and Affordability

At this stage clearly just a guesstimate but based on all my previous work I would suggest we need to consider a 10-15 year programme of perhaps £1-2Bn. Whilst costly  it is not   unreasonable given the very similar estimated costs for the M4 Relief Rd, over £500M to  complete the HoV Road[xxx], plus £000Ms earmarked for other road schemes across Wales; and let’s not forget £50Bn plus for HS2[xxxi] – which we are paying for anyway (5% of £50Bn is £2.5Bn!)

These schemes in totality are likely to have a relatively low subsidy per passenger (as the number of passengers served per mile of operations being high, given local catchment and density of population).

What we need a is formal programme to properly develop a long term and strategic solution

Key Delivery Challenges and Issues

Setting out a range of potential schemes is perhaps the easy bit.  There are some other more challenging institutional and delivery issues that need to be addressed

1 – Road User Charging

There is clearly much more discussion to be had…. but we do need it if we are going to develop and deliver the transport infrastructure to support the mode shift required and to help deliver our collective climate emergency obligations.  Therefore, we have to look at a means to apportion more of the long-term external costs of car use to the user through mechanisms like road user charging. This issue generates much emotion and much ill-informed debate, but we need to get through it. Any revenues secured can be used to contribute to a major capital programme such as that proposed here.

2 – A long-term programme to relocate public sector offices to town and city centres and TOD.

One of the major contributory factors to our high car use has been the development of homes, offices, hospital, etc in locations which can only be accessed by car.  In and around Newport has been badly effected – Celtic Springs, Imperial Park, Langstone, Spytty Park, ICC, Cardiff Gate, (and now Llanfrechfa Grange – which could and should have been located in Newport!). Our planning system has let us all down over the last 50 years.

We need to see over the next 10-year period, more offices and public services relocated back into Newport City Centre (and those that can’t, ensure they are better connected to the PT network). First up would be The Patent Office, ONS, etc.  All would then be much easier to access using public transport whilst at the same time helping to regenerate Newport City Centre!  What’s not to like!

3 – Address complexity of rail development eco-system in Wales AND devolve powers

The elephant in the room is the non-devolved status of rail infrastructure in Wales.  The UK Government MUST devolve full powers and funding to Welsh Government so that it can lead this programme.

Ignoring the politics, it is abundantly clear that Wales’ rail network has suffered decades of underinvestment vs the rest of the UK network.  Wales has received at best 1% of UK rail enhancement investment since privitisation.

Such figures have only formally been maintained by ORR since 2011 and the 1~2% for enhancements calculated since then is, in my view, a high water mark.  Before then the stock answer from DfT/NR was that “we don’t maintain those figures on an all Wales basis”!  However, a closer look at each NR Control Period High Level Output Specification (HLOS), and sadly I have,  makes it clear that the lack of enhancement investment in Wales goes back decades.  I even have a letter from then CEO of NR, Ian Coucher, in 2008/9 trying to defend the situation by talking up the maintenance and renewal spend.  This is not enhancement investment, it’s what NR needs to spend to maintain the network safely in its current form, and even that figure (and still is today) is lower per route mile in Wales than elsewhere in the UK.

I also oft hear politicians say, “we get higher subsidies for rail services in Wales”.  Yes, and this is as a direct consequence of decades of depreciation of the underlying asset Vs the rest of the UK network.  If you dont invest in your network to expand capacity,  reduce journey times and improve reliability (as has happened elsewhere in UK, esp London and SE England) your operations become less efficient, more costly and so attract fewer passengers Vs those parts of the network that have been in receipt of such investment.  The impact, yes, subsidies go up and the “case for investment” for enhancement appears weaker Vs those places on the investment conveyor belt.

As an example, if you are in business making/selling widgets and your competitor has invested in more efficient equipment with greater capacity to make widgets, then he/she can make more widgets and sell at a lower price…. you will go out of business.  So please do not point at subsidies…. it just shows a lack of understanding of the long term link between capital investment and operational efficiency and demand.  This is also true of the wider economy – if you let places wither on the vine then over time your welfare costs go up…Doh!

So, rather than empty rhetoric about the UK Government building the M4 Relief Road (which is a matter for the WG not UK Gov) perhaps they can address the rail devolution issue and underinvestment for which they are responsible.  In advance they should be prepared to discuss with Welsh Government a jointly funded programme to deliver these proposals.

This needs to happen!

As a post script: its issues like the systemic underinvestment in Wales’ rail network by UK Governments over decades, that has turned me #indycurious. If anyone fancies a more political slant…then here’s a blog that may interest you and some more reflections on our wider climate change challenge.

End Notes…

[i]      https://swalesmetroprof.blog/2019/06/12/no-new-m4-so-what-instead/

[ii]     https://swalesmetroprof.blog/2020/04/05/corona-virus-homeworking-and-transport/

[iii]    https://swalesmetroprof.blog/2019/05/01/climate-change-brexit-and-the-economy/

[iv]    https://swalesmetroprof.blog/2018/12/12/wales-rail-network-the-case-for-investment/

[v]    https://gov.wales/sites/default/files/publications/2018-12/the-rail-network-in-wales-case-for-investment.pdf

[vi] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/514912/road-use-statistics.pdf

[vii]   https://swalesmetroprof.blog/2019/06/12/no-new-m4-so-what-instead/

[viii]   https://www.planetizen.com/blogs/107748-better-planning-more-comprehensive-transportation-cost-analysis

[ix]     https://humantransit.org/

[x] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/762976/latest-evidence-on-induced-travel-demand-an-evidence-review.pdf

[xi]     Victoria Transport Policy Institute, Transport Costs and Benefits Analysis https://www.vtpi.org/tca/tca00.pdf 

[xii] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/533293/rrcgb-main-results-2015.pdf

[xiii]   https://www.kcl.ac.uk/news/uk-air-pollution-could-cause-36000-deaths-a-year

[xiv] https://www.europarl.europa.eu/news/en/headlines/society/20190313STO31218/co2-emissions-from-cars-facts-and-figures-infographics

[xv]    https://swalesmetroprof.blog/2017/06/28/driverless-cars-as-a-service-batteries-and-urban-spaces/

[xvi]   https://mgbarryconsulting-my.sharepoint.com/:b:/p/mark/EdoZwNDGSCRDmefTNSN9aGEBRVZNLgunxYvFWUH4d8YUtg

[xvii]   https://statswales.gov.wales/Catalogue/Business-Economy-and-Labour-Market/People-and-Work/Employment/Commuting

[xviii] M4 Corridor around Newport – Updated Public Transport Overview, WG, December 2016

[xix]   https://www.nomisweb.co.uk/census/2011/ks101ew

[xx] https://www.researchgate.net/publication/279298829_Light_rail_transit_and_residential_density_in_mid-sized_cities

[xxi]   Metro Impact Study 2013, https://gov.wales/south-wales-metro-impact-study

[xxii]   https://gov.wales/sites/default/files/publications/2018-12/the-rail-network-in-wales-case-for-investment.pdf

[xxiii] https://gov.wales/sites/default/files/publications/2019-09/a-railway-for-wales-the-case-for-devolution.pdf

[xxiv]   https://gov.wales/written-statement-principles-public-transport-connectivit

[xxv]   https://swalesmetroprof.blog/2020/01/15/cardiff-transport-white-paper/

[xxvi] https://swalesmetroprof.blog/2019/07/05/a-cardiff-crossrail/

[xxvii] https://swalesmetroprof.blog/2019/07/05/a-cardiff-crossrail/

[xxviii]          https://swalesmetroprof.blog/2019/10/01/wg-national-development-framework-some-quick-reflections/

[xxix] https://swalesmetroprof.blog/2019/04/25/transit-oriented-development-in-the-cardiff-capital-region/

[xxx]   https://gov.wales/roads-driving

[xxxi] https://swalesmetroprof.blog/2020/01/07/wales-and-hs2/

5 thoughts on “A Public Transport Grid for the M4 Corridor…

  1. Excellent and convincing analysis. But you should use far fewer exclamation marks! Ideally, none — let the facts make their own point.


  2. Thanks Mark always find your information and analysis really helpful, I’m particularly interested in the connection between Victoria Park proposed new station and Creigiau.

    Do we know yet what the cost will be for that section?

    Is it an additional cost to the funds already allocated to the Metro?

    Will the disused freight line (old rusty lines as we called it s kids) be the preferred option and utilised.



  3. Interesting article. It’s the lack of alternatives which keep people in their cars eg Still cannot travel from Ebbw Vale to Newport direct by train despite years of promises. Caerleon has no train station despite new housing developments, poor air quality, being on a main line and M4 relief road cancelled, no buses past early evening.


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