Land Development Engineering

 View Only
  • 1.  Driveway gradients

    Posted 22-06-2015 21:17
    In the suburbs of Auckland Central we try to limit driveway gradients to a maximum gradient of 1 in 5, occasionally allowing up to 1 in 4.  The expectation is that they will be concreted and on shaded steep areas we will require a rough surface. We require flatter grades at the transition toward the road and manoeuvring areas.  We often have architects and their engineers wishing to exceed these gradients. I am interested to hear what gradients you may allow in your districts and any issues you may have with steep drives.

    Glenn Broadbent
    Auckland Council

  • 2.  RE: Driveway gradients

    Posted 23-06-2015 11:05
    The main issue with steep driveways isn't vehicular access, but pedestrian access conforming to disability standards. When I was working for North Shore City in Auckland I used to insist on a handrail for 1:4 driveways, but I don't think that will pass muster in this day and age. Anything steeper than 1:4 isn't really a good engineering outcome.  

    Darren Price
    Randwick City Council


  • 3.  RE: Driveway gradients

    Posted 29-06-2015 11:17
    Hi Folks.
    I agree that 1:5 is a desirable target, with 1:4 practical with the right surface and transitions. I've had a recent look at some steeper single-user accesses I consented over a decade ago to see how they were going.
    A well-constructed chip-seal rural site entrance at 1:3.4 was still in sound condition, no doubt helped by it's well-drained, open sunny aspect which has prevented moss or lichen growth.
    The steepest residential driveway I know of is 1:2.65 (38%)! This was built by an owner with a large 4WD vehicle to a storage garage to suit his own lifestyle. It is concrete with a striated impressed surface and is completely straight. He uses it OK and if anyone else bought the site they could certainly see what they were buying into. No casual visitors would choose to use it as good kerb-side parking is available. However I don't view this site as a desirable example for normal usage, as any water/moss/leaves/ice etc would make it hazardous, particularly for pedestrians trying to walk up it. I felt comfortable walking up it on a clean surface. The vehicle crossing and footpath on his road frontage is a standard 4%.

    So, I think keep advocating for the usual targets, but 1:3.33 (30%) is probably the maximum I could be persuaded to go to for case-by-case consent on 'normal-usage' driveways considering the long-term risks of moisture/shading/visitor usage etc.

    Roger Stokes
    Development Engineer
    Taupo District Council


  • 4.  RE: Driveway gradients

    Posted 23-06-2015 20:55
    Hello Glenn,

    Christchurch has some very steep locations on the Port Hills and the older established areas and new developments alike have many of the issues we were grappling with in Auckland.
    In my days as a developer's engineer in Auckland I pushed your rules to the absolute limit and then had the joy of driving on the results - in one case daily at my own home.
    I believe 1 in 5 is a sensible limit.
    When a designer tries to maximise the centreline length of an alignment to achieve an acceptable grade between two elevations one method is to use a horizontal curve. A simple C or even an S bend is a longer route than a straight line between two points. So taking this to an extreme if the curves are minimum radius the length may be maximised. A centreline 1 in 5 gradient now becomes 1 in 3.5 or so on the INSIDE wheel track of the minimum radius curve.
    Result is loss of traction or wheel spin for a vehicle going uphill.
    I achieved a private driveway which met Auckland City's maximum driveway gradient and yet an empty wheelbarrow parked on my driveway facing downhill would creep down grade. A 4 cylinder car facing downhill with the handbrake on could be moved merely with the hand pressure of a person .
    Take care when shutting the boot :-)
    At that grade the driveway is functional for a vehicle but not inherently safe for residents nor for unsuspecting visitors.
    The other design trap is the need to maintain a safe sight line when the 1 in 5 gradient transitions to level (use an over vertical curve at the top of the drive).
    This is the same danger whether at the footpath crossing for a property below the road or at the dwelling when the driveway is above the road.
    A driver must be able to see over the car bonnet to avoid running over a child on the footpath or avoid hitting another car parked in the "parking space" at the top of the driveway.
    I realise we do not have many HQ Holdens or P76 Leylands on the road anymore.
    There may be an argument that cars are shorter, turn tighter, climb steeper and driver visibility is better by design.
    The regulators are here to protect the end user (and unsuspecting purchaser) from the clever designer.
    I note you do not distinguish between "private driveways" and commercial buildings where users may be staff or occasional visitors.
    I welcome discussion on if it is appropriate to have the same standard for access to visitors car parks in commercial buildings or a higher standard than residential driveways.

    David Plom
    Synergine Group Limited