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"Traffic flow" - what is it good for?

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  1. chdot
    Admin

    Not sure that we've ever had a specific thread.

    Follows on from 20mph and general 'road space' discussions.

    I'm never clear whether CEC 'believes' in it or uses it as a smokescreen for getting stuff done while still appearing to 'inconvenience' as few 'motorists' as possible.

    There seem to be two sorts -

    1) getting from A to B because there is no alternative (or at least one "I" would consider).

    2) getting from A to a work in "my" car - at exactly the same time as everyone else is doing the same - via a variety of modes.

    'As we all know' Edinburgh doesn't have much of a traffic problem outside 'rush hour'.

    Many years ago Sarah Boyack (as Scottish Minister of Transport) tried to introduce a 'workplace parking tax' (and a supermarket parking one).

    Didn't go down well with the Daily Record (and others).

    Posted 10 years ago #

  2. dougal
    Member

    I don't even know what traffic flow is. Well, apart from a cynical attempt at redefining who belongs on the road in a "might makes right" way.

    It flows, gets slower in cold weather and you can get stuck in it. Traffic is probably treacle?

    Posted 10 years ago #

  3. Chug
    Member

    "Traffic flow" - what is it good for?

    A: "Me, myself and I!"

    © EEN

    Posted 10 years ago #

  4. wingpig
    Member

    They certainly seem determined to configure many junctions to act as reservoirs, perhaps feeling compelled to due to the relatively short segment lengths available in as a compact and non-motorwayified city as Edinburgh. It'd be fascinating to have a play with their data and models to see what might happen if the extra lanes at junctions were all removed overnight, though presumably there'd be a much greater incidence of "sod this, I'll escape up this side street" if that were tried in real life.

    Posted 10 years ago #

  5. kaputnik
    Moderator

    Traffic by its very nature isn't really ever going to flow. I like the treacle analogy.

    Someone really needs to teach CEC's roads designing people the basic logic of human reaction time being a constant, therefore as you increase the speeds the stopping distances (therefore the safe spacing of vehicles) increase also, disproportionately so thanks to the old 1/2MV^2.

    You can pack more traffic into a smaller space if you slow it down, therefore you're more likely to keep it "flowing" if, counter-intuitively, it's going slower.

    Currently they've managed to designed a city centre where everyone is racing to the next red light only to have to slam on the brakes again.

    Posted 10 years ago #

  6. Nelly
    Member

    I drive the family car approx 1 x weekly and have tested (in my own non scientific and slightly pointless way) what happens if I slow down and travel at what I think is a safe and appropriate speed (for me and other road users/pedestrians).

    Unsurprisingly, my journey times are affected so little to be inconsequential. We have seen some evidence of this on the '20mph' debate.

    Equally unsurprisingly I dont get out at the end of the journey wanting to shout and scream at people.

    My observations are that while the planners can position speed reducing measures in town, all that seems to result in is drivers speeding up in between these measures.

    I really dont know how sensible traffic flow is introduced, because in a city this size, it will take a lot of people driving like me to effectively force change on the rest of the population.

    Example - My dad tells me he drives at 30mph through Holyrood Park - in the 20mph zone "unless its not safe to do so".............<sigh>

    Until people look on speeding in populated areaa in the same way as drink driving, I cant see real change.

    Posted 10 years ago #

  7. Arellcat
    Moderator

    You can pack more traffic into a smaller space if you slow it down, therefore you're more likely to keep it "flowing" if, counter-intuitively, it's going slower.

    This is why motorways are given temporary variable speed restrictions to manage reaction times and uniformity of speed and thereby alleviate congestion shock waves.

    I think there is also a parallel with high speed rail. Faster trains move passengers more quickly but require longer signalling blocks if their braking ability remains unchanged, so the trains might also need to become longer to increase the rate of passengers per unit time, but we can't increase the train lengths indefinitely because they're physically limited by the length of platforms, the route loading gauge, and perhaps the length of passing loops. So you end up building entirely new dedicated infrastructure...

    I know from many miles of experience that when motorbiking in Edinburgh, my average speed has tended towards 18mph.

    Posted 10 years ago #

  8. ianfieldhouse
    Member

    I experimented with driving home and never going over 20mph the other day. The main observations I made doing this were:

    1. I didn't take any longer than I would have done driving normally
    2. the cars in front shot off away from me when lights changed and I caught them up at the next junction/lights
    3. any cars waiting to join the main flow of traffic could now do so as there was a gap between the car in front of me and myself
    4. the car behind me drove right on my bumper for the first few minutes before realising I wasn't going to speed up over 20mph so he must have thought that he might as well back off (he was probably raging that I was holding him back — this was a source of great satisfaction to me)
    5. I arrived home feeling nicely relaxed and not stressed out in any way

    If everyone was to drive at 20mph points 2-4 would likely disappear but while the 30mph is still in force people driving like me at 20mph are probably improving the flow of traffic for others as there is less waiting at side streets for a gap to get out.

    Posted 10 years ago #

  9. Arellcat
    Moderator

    5. I arrived home feeling nicely relaxed and not stressed out in any way

    On the occasions that I'm on the motorway or the city bypass, I tend to chug along at about 60mph. There's quite a big comfort difference even between 60 and 70 when you're exposed to the elements, but any 'extra' time taken is much less of a factor. I think many car drivers forget all about there being an outside environment, especially those who belt down the M62 at 90mph (or alternatively, 15mph).

    Posted 10 years ago #

  10. LivM
    Member

    I'm sure I've referenced this before, but my driving is informed by this website: http://trafficwaves.org/
    I try to create a little wave of anti-traffic, by avoiding bunching up and leaving gaps (as per Ian, above). I generally arrive at my destination less stressed too!

    Posted 10 years ago #

  11. neddie
    Member

    Ideally on motorways you want to set the cruise control (sorry) to about 5mph below the average speed of traffic. Then you very rarely have to change lane. Very relaxing.

    Or, get adaptive cruise - even better

    Posted 10 years ago #

  12. Wilmington's Cow
    Member

    While I'd never say its beneficial to make other road users angry (satisfaction that someone was raging?) there was a great study a while back that I'm going to have to try and find that determined driving ten miles under the limit improved flow on motorways.

    That said, I do use cruise control all the time on the motorway (what's 'adaptive cruise control Eddie? Sounds interesting!), but set basically at the limit, unless you're travelling at rush hour (or on the M25), and are able to look and plan ahead, there's never a need to switch it off for miles and miles and miles.

    Posted 10 years ago #

  13. ianfieldhouse
    Member

    >satisfaction that someone was raging?

    Yeah. He was all over my back bumper trying to force me to speed up when it would have achieved nothing. So if he was annoyed, good, because he was driving aggressively toward me.

    Posted 10 years ago #

  14. neddie
    Member

    @WC

    Adaptive cruise allows your car to modify its speed based on the car in front, allowing it to follow the next car at a safe distance. It works by radar. Some systems are able to bring the car to a complete stop if necessary.

    Currently it is available on mid- to high-spec recent VW Golfs & Volvos.

    http://en.wikipedia.org/wiki/Autonomous_cruise_control_system

    Posted 10 years ago #

  15. PS
    Member

    That said, I do use cruise control all the time on the motorway (what's 'adaptive cruise control Eddie? Sounds interesting!), but set basically at the limit, unless you're travelling at rush hour (or on the M25), and are able to look and plan ahead, there's never a need to switch it off for miles and miles and miles.

    I've been doing this for about 5 years now - set the cruise control at 68ish at Abingdon and it can stay there all the way down to Kendal, all being well. It really does make the drive less stressful and exposes the vagaries of human-controlled vehicles (surgers, folk who can't maintain the same speed when the gradient changes, etc).

    Gets less useful once you're south of Preston when the traffic levels tend to build up.

    Posted 10 years ago #

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