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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: Speed limiters
Date: Tue, 9 Jul 2024 17:26:16 +0100
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On 07/07/2024 21:44, Don Y wrote:
> On 7/7/2024 12:09 PM, Martin Brown wrote:
>> On 07/07/2024 18:51, Don Y wrote:
>>> On 7/7/2024 2:56 AM, Martin Brown wrote:
>>>> Investment in "smart motorways" which allows them to use all 4 lanes 
>>>> as live running lanes (3 properly designed to be running lanes and 
>>>> one hard shoulder intended as a refuge for broken down vehicles).
>>>
>>> How does "smart" make that possible but "not-smart" doesn't?
>>> Do your roadways "change directions" based on time of day?
>>> (we have center lanes that do so to expedite traffic into
>>> or out of busy areas based on traffic patterns -- but, they
>>> are time driven)
>>
>> In theory the smart motorways are monitored along their length by 
>> cameras and control rooms. Each lane has a tick or a red cross above 
>> it to indicate if it is in use or not available. At peak times all 
>> lanes are run live which leaves no room for error whatsoever.
> 
> I don't understand -- they are taking capacity OUT of service?

No. In normal conditions it is standard motorway 70mph limit and 3 
running lanes one hard shoulder. When it gets busy the speed limit drops 
to 60 (then 50) and the hard shoulder becomes a running lane.

In that latter mode a cross in a lane indicates an obstruction in that 
live lane so you have better slow down and/or get out of it.
> 
>> Emergency vehicles have to fight their way through traffic if 
>> something happens (as opposed to going down the non-running lane hard 
>> shoulder).
> 
> That seems to be a bigger problem "in town", here.  Largely because
> traffic is naturally stopped at frequent intervals along any travel
> route.  Convincing three lanes of "parked" (at traffic signal)
> traffic to get the hell out of the way for an emergency vehicle
> approaching from behind is a bit of a chore.

UK drivers are mostly quite good about opening a path for emergency 
vehicles. What they don't do well is zip merging.
> 
> Such vehicles are equipped with a strobe light that visually signals
> a sensor mounted high in the intersection.  It ties in to the local
> signal controls and overrides the timing to allow traffic along
> the "approach axis" to move, even if it would normally be halted.

Nothing like that here or if there is then it is cryptographic. Where I 
live the PM (previous) moves about quite a lot and it is done by 16x 
police motorcycle outriders going ahead and escort vehicles followed by 
a bunch of heavies.

> In theory, that traffic starts moving (making the blockage more
> fluid) and they can then get out of the way of the approaching (from
> front or rear) emergency vehicle.
> 
> Too often, drivers "freeze" thinking that the emergency vehicle can
> sort out its dilemma.  For undivided roadways, the emergency vehicle
> will often cross the centerline to use the lanes in the opposite
> direction to get around idiot drivers "ahead" of it.

The drivers freezing is silly places problem is common in the UK too.

>>> Most roads have predefined lanes in each direction.  Some roadways
>>> are further (physically) "divided" to isolate traffic from each
>>> direction.
>>
>> UK motorways have strict central reservation barriers which are being 
>> reinforced to heavy weight solid cast concrete with tensile steel 
>> inside to stop the larger HGVs going straight through them.
> 
> Our "interstate" highways tend to have a large median between divided
> lanes.  So, crossing over the "center line" ends up with a vehicle
> in grass/ditch.

We don't have enough real estate for that. Motorways where the opposing 
lanes are more than 10' apart can be counted on the fingers of one hand.

> Of course, this is only possible in places with ample real estate.
> Such roads traveling through metropolitan areas can be hazardous as
> the concrete "prisms" placed end to end are really only massive enough
> to *deflect* traffic, not *stop* it.
>> That is the point of "smart" motorways. There is no hard shoulder to 
>> pull off onto - it is a live lane just like all the others. You can't 
>> always control where you breakdown either. There are refuges from time 
>> to time but far too far apart to be any use.
> 
> Ah.  Most roads, here, have a shoulder -- though sometimes "soft".
> It is not uncommon to see someone trying to change a flat tire on the
> driver's side ("in-side" of the roadway) of their vehicle.  A patrolman
> will "run interference" for you *if* he comes upon you.  Otherwise,
> you work with one eye always watching oncoming traffic.
> 
> Police officers are often at risk in roadside stops as the *vehicle*
> may be on the shoulder but the officer standing beside the driver's
> door/window will have his ass out in traffic.
> 
> ["distracted drivers" care little about what they may hit!]

UK the advice is to get out of the car and stay behind the crash 
barrier. Cars on the hard shoulder get hit with monotonous regularity.

>>> A patrolman encountering such a vehicle will likely park his vehicle
>>> upstream of it to further alert oncoming traffic to the hazard.
>>
>> Same in the UK. Highways agency vehicles have damn big flashing please 
>> don't hit me signs with an arrow that can be erected behind them.
> 
> Police will usually walk back upstream and deploy flares to warn of their
> stationary presence, "ahead".

Similar but no flares. HGV's will protect a serious crash site though 
I've only been in one major incident as the first car to stop without 
hitting anything and was then protected by the HGV behind me.

It was reported as 3 HGVs and a car. But it was actually a single car 
that clipped the central reservation 2 or 3 times and then swept across 
the live lanes totalling a couple of cars as it went. The HGV driver 
behind me had a QD dashcam with higher viewpoint which was used in evidence.

It is reckoned that for every hour of stationary traffic queue on a UK 
motorway there will be one serious rear end shunt (in addition to the 
original incident that caused the queue). Sometimes rubberneckers on the 
other carriageway cause a separate incident.

-- 
Martin Brown