M4 Design

BrianD3

I noticed a couple of things about the M4.

At the side of each carriageway there are wide flat grassy areas in a lot of places. If a car or truck were to break down or lose control at one of these points there would be a lot of space to slow down/pull in completely off the carriageway. I wonder are there going to be trees planted in these spaces though. I think they should be left as they are.

However at other points there are embankments and drops. Some are protected by barriers, others aren't. If a vehicle were to lose control at one of these points and go off the side of the road into a drop at motorway speeds it would result in a big roll and probably a fatality.

The other thing is the lack of road markings at the toll plaza - a huge expanse of road with no white lines. When I drove the motorway it wasn't that busy yet there was still a free for all as drivers swerved around looking for the least busy toll booth and then "jostled for position" as they exited the booths. I know similar carry on happens on the westlink where there are road markings still I think the road markings do result in at least some order.

Anyone else have any comments on the design of this road. Overall I think its good.

impr0v

BrianD3 wrote:

I noticed a couple of things about the M4.

At the side of each carriageway there are wide flat grassy areas in a lot of places. If a car or truck were to break down or lose control at one of these points there would be a lot of space to slow down/pull in completely off the carriageway. I wonder are there going to be trees planted in these spaces though. I think they should be left as they are.

However at other points there are embankments and drops. Some are protected by barriers, others aren't. If a vehicle were to lose control at one of these points and go off the side of the road into a drop at motorway speeds it would result in a big roll and probably a fatality.

The other thing is the lack of road markings at the toll plaza - a huge expanse of road with no white lines. When I drove the motorway it wasn't that busy yet there was still a free for all as drivers swerved around looking for the least busy toll booth and then "jostled for position" as they exited the booths. I know similar carry on happens on the westlink where there are road markings still I think the road markings do result in at least some order.

Anyone else have any comments on the design of this road. Overall I think its good.

It was a stipulation of the PPP contract that the motorway be designed in such a way so as to allow for a relatively painless upgrade to three lanes, this is obvious in certain areas of the scheme and not so obvious in others. As far as I am aware all planting is complete at this point so the areas you refer to will more than likely remain as is.

I noticed some spots that I thought should have barriers also, but the scheme design has passed 4 (perhaps 5) stages of safety audits so there are presumably bona fide design and economic reasons for not putting them in those places.

The lack of markings at the toll plaza struck me as highly unusual and potentially dangerous, however there were plans to line it as per standard practice but the safety auditors recommended leaving it as you now find it. They claimed that English practice and/or latest industry advice is that there are less accidents with no lines. I suppose an argument could be made that it means every driver must concentrate on the line they are taking and where other vehicles are with respect to them. I personally found it unnerving to be unsure exactly where to aim for, traffic in front of me having blocked my view of where the road became two distinct lanes again.

mackerski

I've seen toll plazas in France with no lane markings. It struck me as a sane approach, in that if forces driver attention. Speeds should be low enough to cope anyway.

Dermot