Ridiculous on/off ramp speed limits

highdef

OK, bit of a rant about the inconsistent speed limits on some motorway on and off ramps. Some appear to be way too low for the stretch of road in question whilst others are dangerously high. I have two examples:

Exiting junction 8 southbound on the M9 (heading for Waterford but making a pit stop in Kilkenny) a few months ago, I was on the off ramp and passed these 80kmph signs:
https://www.google.ie/maps/@52.635526,-7.142439,3a,75y,205.69h,77.59t/data=!3m4!1e1!3m2!1s5-1iBF8ZwbFebTqU3djfDQ!2e0 so I made the reasonable assumption that whatever bends were coming up could be easily negotiated at 80kmph so I set the cruise control to 80. However a much tighter than expected bend appeared before me - https://www.google.ie/maps/@52.633616,-7.143354,3a,75y,219.13h,70.73t/data=!3m4!1e1!3m2!1sEMF9-xSkquMZ6BKFHdg8bg!2e0 and I had to hit the brakes.
As bad as that was, when I was returning to the motorway a while later to continue my southbound journey, the same speed limit signs https://www.google.ie/maps/@52.634102,-7.147303,3a,75y,84.05h,82.77t/data=!3m4!1e1!3m2!1sdVsgZCgFmQ7xENyN-HfRTg!2e0 applied for an even tighter and longer turn off some 270 degrees. I had noted this from the experience already mentioned above so I was nowhere near 80kmph, in fact was nearer 40kmph - https://www.google.ie/maps/@52.634199,-7.143286,3a,75y,329.36h,71.97t/data=!3m4!1e1!3m2!1s4SRdDOSa8XTvO1cvogYEXg!2e0

And yet, if joining the M50 southbound from the M1 southbound, the slip road is way way more gentle and can easily be done at 60kmph (maybe even 80kmph for cars and small vehicles anyway), yet it has a 30kmph limit!!! Note in the following link, the current 30kmph speed limit signs had not been installed - the limit at the time the streetview photos were taken was 50kmph - still slow but not too bad -https://www.google.ie/maps/@53.409332,-6.225037,3a,75y,213.72h,84.36t/data=!3m4!1e1!3m2!1s_paqv0hhw1ZBn3bE_wjfKw!2e0

_Kaiser_

Regardless of what a sign says, you should always be ready for something unexpected - setting cruise control when leaving/joining a motorway isn't something I'd do myself either.. only when on the mainline and when traffic is light enough to allow it without having to constantly override it.

I agree with you though that a lot of the exits/on-ramps are a mess .. badly designed with bends that are too sharp (N7-M50 for example) or not enough run-off/merge space (Junction 10-9 on the M50 North) thus defeating the whole idea of "free flow". AFAIK the stupidly low limit on the M1 one is because trucks have overturned on it.

highdef

Well there were no other cars on the road and as soon as I saw that the upcoming bend was not going to be navigable at 80kmph, I began braking. I knew from the sat nav that it was a free flow junction. That plus the 80kmph sign gave me the impression that it would be a nice wide curve around which it certainly was not. Even if I had not been using the cruise control, I would have aimed for about 80kmph upon seeing the sign, thinking the merge would have been like a slightly sharper version of say the M9 to M7 merge, which I think is 120kmph but could be wrong.

As for the reason behind the 30kmph speed limit on the M1 merges, I had heard that too but can't see the logic in it whereby every vehicle must slow to a virtual crawl. Why have a 30kmph limit when 60kmph or more is easily done and then conversely have an 80kmph limit at another junction where 40kmph is barely attainable.....the mind boggles

foggy_lad

A vehicle must not be driven at a speed exceeding that which will enable its
driver to bring it to a halt within a distance the driver can see to be clear.

the speed limit is not a speed that you must or even should drive at!

meathstevie

foggy_lad wrote: »

A vehicle must not be driven at a speed exceeding that which will enable its
driver to bring it to a halt within a distance the driver can see to be clear.

the speed limit is not a speed that you must or even should drive at!

Yeah, exactly, on most Irish slip roads entering a motorway you should substantially exceed the speed limits posted in order to join the motorway at a safe motorway speed.

markpb

highdef wrote: »

As for the reason behind the 30kmph speed limit on the M1 merges, I had heard that too but can't see the logic in it whereby every vehicle must slow to a virtual crawl.

If it's only safe for trucks to manage at 30kph, the lines of sight must be pretty bad meaning that you might not see a truck ahead of you. Setting a 60kph limit would encourage other drivers to take the corner at that speed (as you said yourself), not realising that there may be a much slower vehicle ahead of and invisible to them.

You're right, they should not have been built like that and 30 is very slow for a motorway on-ramp but there's plenty of room to accelerate up to speed (in my experience, driving a pokey 11yo 90bhp estate) and sometimes things aren't always built perfectly because of valid reasons which we don't like but must now live with (like gyms built beside motorway intersections).

meathstevie wrote: »

Yeah, exactly, on most Irish slip roads entering a motorway you should substantially exceed the speed limits posted in order to join the motorway at a safe motorway speed.

That's certainly not true on the M50. For big chunks of the day, if you try joining at/near the limit, you'll rear end someone doing 60 on the inside lane.

Dravokivich

markpb wrote: »

(like gyms built beside motorway intersections).

That damn thing should have been demolished years ago. No one has any interest in taking it on at all. It's just going to keep on sitting there.

highdef

foggy_lad wrote: »

A vehicle must not be driven at a speed exceeding that which will enable its
driver to bring it to a halt within a distance the driver can see to be clear.

the speed limit is not a speed that you must or even should drive at!

Yes, but I was driving at a speed that I could bring my car to a halt within a distance I could see to be clear up to the point where I saw that the upcoming bend was a LOT more than I was expecting based on the speed limit that was imposed upon me. As soon as I saw the sharp bend, I decelerated fairly quickly to a safe speed.

What I'm trying to say is that it is very misleading to have an 80kmph speed limit sign on a free flow slip when it would be extremely dangerous to travel at or even close to that speed.

As for the M1 to M50 slip with its 30kmph speed limit - "If it's only safe for trucks to manage at 30kph, the lines of sight must be pretty bad meaning that you might not see a truck ahead of you. Setting a 60kph limit would encourage other drivers to take the corner at that speed (as you said yourself), not realising that there may be a much slower vehicle ahead of and invisible to them." - I can assure you the sight lines are good to excellent - https://www.google.ie/maps/@53.410484,-6.224584,3a,75y,181.47h,80.06t/data=!3m4!1e1!3m2!1slvmtQmomdz0lxk9injlIZA!2e0 I believe the adjacent free flow slip which is from the M50 northbound to M50 port tunnel bound is also a 30kmph limit but not positive and as can be seen, sight lines are also fine - https://www.google.ie/maps/@53.411828,-6.224994,3a,75y,152.79h,87.26t/data=!3m4!1e1!3m2!1s0zy2qBXx-ANQbQGFB4hMCw!2e0

Compare those with junction 8 of the M9 that I was talking about, bearing in mind the 80kmph posted limit: M8 south to N10 - https://www.google.ie/maps/@52.633545,-7.143426,3a,75y,229.15h,84.67t/data=!3m4!1e1!3m2!1ss90LuuLq402ciwMelRNptg!2e0
N10 to M9 south - https://www.google.ie/maps/@52.633483,-7.14503,3a,75y,91.19h,94.28t/data=!3m4!1e1!3m2!1smyHnmMJu6Jc7_ZVGvzzU5w!2e0

Carawaystick

M1S->M50W is a 50 limit. M50E->M50S has a wider radius and so I'd be shocked if it had a lower limit
this suggests a 50 limit...

There should be no pandering to drivers to set a limit to the road, Drivers should drive as they see the road and not what some councillors decided. Otherwise the limit will be set by the worst handling most unstable traffic the road carries ( for liability reasons)

Victor

As speed limits are likely to be revised around the country, now is the time to bring things like this to the attention of the councils involved (and the NRA where it is a national road).