Road Safety Discussion

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  • 1.  Speed dips instread of humps

    Posted 17-04-2014 11:14
    I have been advised that in the United States in some areas they have dips (not for stormwater conveyance) rather than speed humps.

    The width & depth is in relation to the signposted?? travel speed.

    Has anyone had involvement with or trialed these here?

    Adam Mularczyk
    Team Co-ordinator Development Engineering
    Wyong Shire Council


  • 2.  RE:Speed dips instread of humps

    Posted 22-04-2014 10:26
    I have not seen that style but one problem could be reduced visibility. A raised hump with pavement markings is easier to see than thin air. 

    Another problem could be construction of the pavement depth especially in retrofit situations. A hump is easily added over the existing pavement whereas a dip is a locally thinner (or deeper) pavement that needs to reinforced for both normal traffic loads and impact loads.

    Having said all that, I live on a corner block at a T intersection in a quiet suburban area. There are hoons who love to race around nearby streets.  I've got a concrete spoon drain across the base leg and it is really good at enforcing slow speed around the corners. The hoons don't come anywhere near that intersection & no-one has lost it on the corner crashing into my place in the 12 years I've owned it.

    Residents elsewhere often complain about the noise of new speed humps. But the little bit of noise from cars scraping on the spoon drain, that I quickly learnt to ignore, is well worth the cost to keep the hoons away from my place.

    Regards IC.

    Iain Cummings
    Senior Transport Infrastructure Officer
    Gold Coast City Council
    Gold Coast QLD



  • 3.  RE:Speed dips instread of humps

    Posted 28-04-2014 11:08
    An old favourite, this one!  "Humps vs sumps" was a big topic back 30 or so years ago.  There are plenty of "accidental" examples of dips (channels, sumps...) where, as Iain describes, drainage channels are continued across at an intersection.  Adelaide, with its slight drainage gradients, has plenty, or at least used to. Way back there were examples of constructed dips at one if the universities - WA I think.  The problem we found was that sumps operate more like short speed bumps and are thus mostly effective at low speeds, if at all.  Like bumps, they work because they cause a thump in the suspension and have little pitching effect on the vehicle (driver discomfort), which is the mechanism by which calibrated humps work.  Iain puts his finger on the two practical problems: visibility and construction difficulties.  Put one of these in and you'd have fun removing it later.  Having had to fend off perceptions of safety problems with humps for cyclists and motorcyclists, I wouldn't be too confident that you could sell dips to that sector of road users. As a cyclist, i know what I would prefer. I can't imagine how you could adapt them for buses.

    The bottom line is that dips/channels/sumps are not included in the devices found in practice in the Austroads LATM Guide or the Australian standard, and they did not come out too well in ARRB research over the years..  You'd be on your own if it ever became a legal issue.

    Ray Brindle
    Editor, "Road and Transport Research"
    ARRB Group
    Malmsbury VIC


  • 4.  RE:Speed dips instread of humps

    Posted 22-04-2014 10:26


    Many years ago on a road in a education institution, some dips were installed to reduce speed on the approach to a bridge ( sight distance over bridge was nothing useful ).

    While the dips generally slowed down cars, some tried to work out what speed was needed so you could get across without feeling much of a dip, effectively jumping the gap. The dips also slowed down slow vehicles such as tractors, who were allways within stopping sight distance.

    That trick doesn't work so well on humps.

    Probably little difference on scraping and bus passengers vertical acceleration in humps or dips.

    Jim Turner
    "Team Leader, Design & Projects"
    Ku-ring-gai Council