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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: Speed limiters
Date: Sun, 7 Jul 2024 20:09:45 +0100
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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.

Emergency vehicles have to fight their way through traffic if something 
happens (as opposed to going down the non-running lane hard shoulder).
> 
> [IIRC, DC? had similar roads that would change direction
> based on time of day]

There were a few of those in the UK. One in Manchester London Road 4 
lanes under flow control depending on the time of day. 3 in for morning 
rush hour and 3 out in the evening they were notorious for head on 
crashes. Picture from the late 1970's:

https://www.flickr.com/photos/gmts/33623521145

An even worse configuration in the 1970's was the three lane trunk road 
with the centre lane for "overtaking only". They resulted in the most 
spectacular head on crashes (think 150+mph closing speeds) and caused 
collateral damage in the adjacent lanes. Not survivable.
> 
> 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.
> 
>> It didn't take account of dumb drivers or of the need to properly 
>> maintain the camera systems used to monitor the road situation. As a 
>> result they are having to add a lot of extra refuges to the "smart" 
>> motorways to make them safer after several very high profile nasty 
>> high speed collisions between motorway traffic and broken down vehicles.
> 
> Stopping *on* the roadway is often forbidden.  Your vehicle must be
> pulled off, onto a shoulder (outside the outside lane -- far right in
> our case).

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.

In my student days we got stuck immediately behind a vehicle in the 
outside lane (long before mobile phones). What happened next was very 
interesting. A pair of heavies saw what had happened from a distance 
behind us and created a rolling road block. When they had stopped all 
the traffic we got out and pushed the dead car onto the hard shoulder 
and then got back in our car and continued our journey. It was touch and 
go whether someone would pile into us when we had to stop like that.

> 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.

> Work on the roadways (overhead signage, pavement, etc.) usually results in
> overly long stretches being cordoned off ("dunce cones") to ensure traffic
> is clear of the work area BEFORE encountering it.

There is a lot more of that work at the moment because of the crisis 
with smart/dumb motorways. They are dumb as hell when the smarts that 
are supposed to keep them safe are not working!
> 
> And, most roadways enter and exit on the outside (right) lane so you
> can predict where the "varying" traffic will originate.

Opposite sense in the UK, but we do have a few free for all junctions on 
urban motorways where traffic is injected and must leave from the 
outside (fastest) lane. A recipe for high speed collisions.
> 
>> The smart motorways I drive regularly I have such totally misleading 
>> and misguided signs that I no longer trust them to tell the truth. 
>> Worst example I saw was alternate gantries showing 40mph speed 
>> limit(as low as it actually goes on a motorway) and 60mph. I think the 
>> control room were messing about to see what traffic chaos they could 
>> cause.
> 
> The closest thing to "smart" here is signage that may dynamically
> reflect some condition of interest (amber/silver alert, construction
> ahead, etc.).  We have some automated technology that warns of haboobs
> in areas prone to them as they instantiate in time frames too short to
> erect manual signage (radar).  I'd wager there are parts of the midwest
> where similar systems warn of tornados.

They could be a useful if they were properly maintained and drivers 
understood them. Unfortunately neither condition is met in the UK.

There are also variable speed limit motorways and roads equipped with 
the latest average speed camera technology. That is also part of smart.

-- 
Martin Brown