Heavy Haulage Association

Designing NZ’s Roads for Oversize

By Jonathan Bhana-Thomson – chief executive, New Zealand Heavy Haulage Association

Road safety improvements and new projects such as the new Manawatu-Tararua Highway (pictured) need to be designed taking oversize loads into account.

TO ENSURE THAT NEW ZEALAND ROADS CONTINUE TO ALLOW

oversize freight loads to be moved, the Heavy Haulage Association is a strong advocate for designing new road projects and safety improvements that accommodate large loads.

The NZTA Speed and Safety Improvement Programme is a significant investment in safety changes on State Highways, and at the same time it presents a number of challenges to ensure the proposed changes allow for oversize loads to be transported. The association has been engaging with NZTA to ensure that at both a high level, and also with individual projects, that allowances are made in the designs.

The most significant imposition (and also NZTA says some of the greatest safety benefits) come from median wire rope barriers being retrofitted to existing roads. Where these roads are one-lane in each direction, then the challenge comes when ensuring that wide loads up to 11-metres width can be accommodated without needing to hang over the barrier on frequent occasions.

Roadside restrictions such as light poles, trees, signage and cut banks can reduce the side clearances – and these are all challenges the NZHHA puts to the designers to mitigate these restrictions. In a recent example on SH1 (just south of the Karapiro area), we asked the designers to shift the position of the barrier to try to gain more clearance. And north of Auckland in the Dome Valley, a high voltage power pole is proposed to be shifted to ensure greater clearance in the north-bound lane.

Another key safety mitigation that NZTA proposes at higher risk intersections are roundabouts. Where there is one circulating lane around the roundabout, then the association seeks that while they are designed for the largest usual heavy vehicle, a check is completed using a rows of eight and load divider, to ensure that this can still track around the roundabout.

Often this means there needs to be designed-in mountable areas around the inside of the roundabout as an apron, and the location of islands on the approaches needs to be designed around the swept path of these vehicles.

Meanwhile the location of light poles and signage around the roundabout needs to cater for those wide oversize loads. This has been achieved in many locations around NZ where there has been vehicle tracking carried out – such as on the new ManawatuTararua Highway, the SH6/8B intersection near Cromwell, and the Princess Street roundabout on SH3 near Waitara.

The association has been working with NZTA to ensure the design guidelines for the Safety Projects makes allowances for the transport of oversize freight upfront, so that individual projects start with a suitable design template. The association can then provide guidance about the use by oversize loads of that specific location – to ensure that any special requirements for exceptional over height loads for example is provided for.

This is still a work in progress but we are committed to working with NZTA project managers and designers to ensure that the future for the transport of oversize loads remains open. T&D

Jonathan Bhana-Thomson