M49 Southbound Car Park.

[AAndy]

Heads-up to anyone traveling in normal hours from the M4 South Wales to M5 heading for the South West: The M49.

The M5 Bottleneck from Gordano to Clevedon southbound is having a huge knock on effect to the flow of the M49 which has become a real problem in the last 18 months. Even when the M5 is slow moving the M49 grinds to a halt. Yesterday the M5 was flowing south, probably at 25-40mph but the m49 was blocked back the the Amazon roundabout....just queuing to get into the one lane feeder to the M5 4 lane.

And I've noticed it many times during the past 18 months.....prior to 2023...never saw a queue once on the M49.

So check traffic first .....I head along the M4 around the Almondsbury interchange and down the M5 from there when necessary now.

[DB617]

How peculiar. Have you been able to observe whether the weaving movement between the M5-A4 traffic is the problem or the mainline? It's a lane gain, so doesn't make a great deal of sense.

[SteelCamel]

How peculiar. Have you been able to observe whether the weaving movement between the M5-A4 traffic is the problem or the mainline? It's a lane gain, so doesn't make a great deal of sense.

The M49 southbound entry isn't a lane gain. The lane gain is at the previous slip where the Avonmouth Spur enters. I'd suspect that if traffic is moving slowly, the mainline traffic will move into the left lane as soon as it's clear of the lane gain, so there's a queue by the time traffic reaches the M49 entry slip. As the M5 has priority at the merge, if people don't let joining traffic out then the M49 will back up. I wonder if it would be improved by a barrier between the new lane and the three main lanes until after the second slip, to stop the M5 traffic getting into that lane too soon.

[DB617]

How peculiar. Have you been able to observe whether the weaving movement between the M5-A4 traffic is the problem or the mainline? It's a lane gain, so doesn't make a great deal of sense.

The M49 southbound entry isn't a lane gain. The lane gain is at the previous slip where the Avonmouth Spur enters. I'd suspect that if traffic is moving slowly, the mainline traffic will move into the left lane as soon as it's clear of the lane gain, so there's a queue by the time traffic reaches the M49 entry slip. As the M5 has priority at the merge, if people don't let joining traffic out then the M49 will back up. I wonder if it would be improved by a barrier between the new lane and the three main lanes until after the second slip, to stop the M5 traffic getting into that lane too soon.

Ah, yes. My mistake.

Even just keeping the mainline and slips separated as you describe, but by an extended hatched area (tiger tail?) would probably work. The flow from the Avonmouth Spur is not that significant compared to the M49. It can't be - it's fed by a pair of roundabouts less than a kilometre away.

Unfortunately the Bristol motorways are a cornucopia of awful design, markings, signage and maintenance. It's remarkable things were done the way they were. Case in point, the fact the M4 is D2M between the M5 joining and the M48 leaving. Massive waste of potential probably simply due to "sChEmE bOuNdArIeS" when designing the 2nd crossing and links.

[Chris5156]

Case in point, the fact the M4 is D2M between the M5 joining and the M48 leaving. Massive waste of potential probably simply due to "sChEmE bOuNdArIeS" when designing the 2nd crossing and links.

It is strange - and stranger still that there's never even been a suggestion of correcting it with a relatively short length of widening.

The traffic count on the length between M5 and M48 is about 60k, which is equal to the Second Severn Crossing (D3M).

[jackal]

Case in point, the fact the M4 is D2M between the M5 joining and the M48 leaving. Massive waste of potential probably simply due to "sChEmE bOuNdArIeS" when designing the 2nd crossing and links.

It is strange - and stranger still that there's never even been a suggestion of correcting it with a relatively short length of widening.

The traffic count on the length between M5 and M48 is about 60k, which is equal to the Second Severn Crossing (D3M).

Aren't there bits of the D2M A1(M) at 80k aadt? And this bit of the M5 is three lanes eastbound, so not really D2M. Of course I agree it would ideally be improved.

Have you been able to observe whether the weaving movement between the M5-A4 traffic is the problem or the mainline?

This could be removed by giving the M49 an earlier diverge for the M5 from the right (lane drop), with the current diverge for the M5 from the left closed. A bridge at Kings Weston Lane would be required so it may not be too cost effective, but it's curious it wasn't originally built like this.

[AAndy]

Working out the queue effect reasons is a head scratcher ......I've seen it most around early to mid afternoon.
The M5 2 lane exit to Avonmouth which merges to become the single lane M49's M5 slip is also an ingredient.

Perhaps more traffic is using the M5 exit AND the M49 (poss increase due to the lifting of the tolls).

[Bryn666]

Case in point, the fact the M4 is D2M between the M5 joining and the M48 leaving. Massive waste of potential probably simply due to "sChEmE bOuNdArIeS" when designing the 2nd crossing and links.

It is strange - and stranger still that there's never even been a suggestion of correcting it with a relatively short length of widening.

The traffic count on the length between M5 and M48 is about 60k, which is equal to the Second Severn Crossing (D3M).

Aren't there bits of the D2M A1(M) at 80k aadt? And this bit of the M5 is three lanes eastbound, so not really D2M. Of course I agree it would ideally be improved.

Have you been able to observe whether the weaving movement between the M5-A4 traffic is the problem or the mainline?

This could be removed by giving the M49 an earlier diverge for the M5 from the right (lane drop), with the current diverge for the M5 from the left closed. A bridge at Kings Weston Lane would be required so it may not be too cost effective, but it's curious it wasn't originally built like this.

The eastbound 3 lanes is a climbing lane that got gobbled up to become an auxillary lane between the M48 and M5 - the M49 presumably made it "not needed". I've never quite worked out how you can build so many motorways around one side of a city and still make none of them connect properly.

[A303Chris]

Interesting as I have never been caught up there. When there is a queue on the M4 westbound onto the M5 southbound I always go M4 / M49 as I've found it so quick and the reverse coming back if there is queue up the hill on the M5 from the M49 to Cribbs Causeway.

[AAndy]

Interesting as I have never been caught up there. When there is a queue on the M4 westbound onto the M5 southbound I always go M4 / M49 as I've found it so quick and the reverse coming back if there is queue up the hill on the M5 from the M49 to Cribbs Causeway.

Yes, up until the beginning of last year I'd say, 2023, I never have seen any queuing on the M49 so always used to use it to avoid the M5 past cribbs when needed. Here is a video from this week: https://youtu.be/k3ETpfarfes