Train Capacity London to Cardiff

When are you thinking of travelling? 12 noon on a winter weekday, or 5pm on the Friday before a bank holiday? Demand makes a big difference as to the crowding of the train as effectively the capacity remains much the same, except for as it is at present where maintenance is being done reducing the frequency from normal.

I very much doubt that renting a car from Central London would be a sensible alternative to taking the train. Standing does happen occasionally but assuming you can specify a particular train you can book ahead for best prices and they will come with seat reservations.

There are also buses to Cardiff run by National Express, Flixbus and Megabus.

The National Express ones are usually first stop Newport (Gwent) straight down the M4 unless they also have a Heathrow pick up. Usually there is a quick driver change at Membury Services but it isn't a passenger stop.

Apart from the terminus at Sophia Gardens inbound they also stop at Cardiff Castle.

Sometimes GWR put boarding controls in place at Paddington (ticket holders with seat reservation only) if they think a Cardiff Concert, like Billy Joel that you are going to, will cause capacity issues.

As has been said there is a difference between travelling at 5 pm on a Friday as opposed to say 1100 on a Tuesday.

Yes there can be standing on this line because at peak times it’s a very busy route. Book a seat for a train that’s running in the middle of a week day and you’ll be fine. Even on a busy train if you have a seat booked then you’ll be able to sit. However if it’s really busy it’s not as nice as being on a quieter train.

You would not be better off renting a car if just going city to city - as seems to be the case with your query. Renting a car is really useful if wandering around villages/countryside. Traffic jams often occur on the M4 at a pinch point at the Newport Tunnel - which also affects buses.

Usually there are two trains per hour between London (Paddington) & Cardiff and they do the journey in about 1 hour 50 minutes. Pre book specific trains ahead to get the lowest prices. Note that events can ramp up demand/prices as can travelling at peak times.

The train company is GWR and you can pre-book seats. Advance specific train fares (non refundable) usually rise in price.
https://www.gwr.com

Some sites will tell you if splitting the ticket works out cheaper - even though you stay on the same train throughout.https://www.traintickets.com/?/
https://trainsplit.com
https://www.thetrainline.com/

The main operator of buses (coaches) on this route is >https://www.nationalexpress.com/en but they will take quite a bit longer than the trains.

Regarding the traffic jams mentioned by James, I am used to going over the Severn Bridge by bus and have never encountered it.

In fact I am used to running early in both directions. That suggests that the possibility is already built into timetables. But also because all buses call into Newport so miss that section of the M4.

We also know that you are not going both ways as you then continue by air to Ireland.

On your travel day, 8 August, most trains from Paddington to Cardiff are £28.05 on Advance Tickets currently or £46.50 in 1st class - (railcard fares) not a big difference for a better seat, included food and drink, allegedly better wifi and pre and post journey lounge access for 1 hour at either end. So £18.45 extra for 1st class.
Both classes give a guaranteed seat.
The 1116 train is £23.40 standard class and £34.65 1st class. That arrives at 1317, nice time to check into your hotel. So for £11.25 you get a better seat, refreshments et al and an overall quieter environment. Even if the train is full and standing due to unbooked passengers then that is very unlikely to happen in 1st class. No sensible person would pay extra to stand in 1st class.

Try renting a car, plus the petrol/gas for that money.

National Express that day are £10.90 on most buses, £8.90 after 12 noon (being over 60 and a fairly regular user I pay 1/3 less than that). That difference shows why I often go by bus, but is not a big difference to you on vacation.

Anybody who doubts what I say about jams on the M4 around Newport can check out Google Maps with Traffic enabled. Yesterday, for example, the westbound M4 was jammed with stop/start traffic all the way from the Severn Crossing to the tunnel at Newport. Media Wales reported that it was taking 50 minutes just to drive a few miles. Eastbound was not good either.
(Remember to account for time zone differences).

That part of the M4 is always bad whenever I go that way. The road narrows to 2 lanes so it’s inevitable. I’m not sure why it could be contentious to say that. It’s very well known.

We are in London from a Monday, (hoping to arrive at our hotel by 1pm), leaving for Wales on a Thursday morning.

From another of OP's postings

Yes,

Arriving on Monday 5 August, to Cardiff Thursday 8 August, Billy Joel Concert on 9 August, fly from Bristol to Dublin Saturday 10 August, Oscar Wilde House 10 or 11 August, drive to Tulla (Limerick/Ennis area) 11 August to stay to 16 August (one of the days 12 to 15 August is a day trip to Cobh for the Titanic/Lusitania/emigration story).

The OP is still looking for ideas for the other 3 days in Tulla on this post- https://community.ricksteves.com/travel-forum/ireland/is-the-heritage-centre-in-cobh-worth-the-trip

Then return to Dublin on 16 August to fly to Iceland for a short stay there on the way home.

It is interesting that even on 9 August train prices to Cardiff from London are still at normal levels just 4 weeks out, as are bus prices. They are not currently showing signs of being unduly busy.

On 9 August National Express are running Event buses to the Stadium from Birmingham, Swindon/Bath/Bristol, Birmingham/Worcester/Gloucester, Swansea and Plymouth/Exeter/Taunton but not from further afield.

EDIT- Looking back this is a family of 4, so the train fares for London to Cardiff and Cardiff to Bristol will be even cheaper than quoted above by using Group Save discount.
But whether that fact (multiplying the train fare by 4), which had been forgotten, skews the decision towards driving from London to Cardiff to Bristol, is a decision for the OP. It certainly makes it less clear cut and may depend on parking availability where the family are staying in Cardiff.

Hello, we have secured very affordable train tickets! A little time rearrangement, but it will be fine. Thanks for all the input, everyone!

That’s good news indeed. I was concerned that you would hire a car and try and & drive into central Cardiff where parking would be expensive for longer stays. Most streets in the city centre are pedestrians only & on the day of the concert, more streets will be sealed off to traffic.

A topless double decker bus is operating in Cardiff this summer - although I guess not on the day of the concert?https://www.cardiffbus.com/skycar-open-top-bus-returns

James, thank you for this link!

"Regarding the traffic jams mentioned by James, I am used to going over the Severn Bridge by bus and have never encountered it. "

James did not mention the Severn Bridge, he clearly stated the pinch point is around M4 around Newport and the Brynglas tunnels to and fro Cardiff, which will be worse when there is an event on at the MillStad, he is correct. Having lived in Cardiff and routinely travelled on that stretch of the M4 more times than I can remember, the traffic is horrific there. The National Express coaches get caught up in the congestion, as the exit they use in either direction to get to Newport on the M4 is directly either side of the tunnels.