New Zealand Transport Agency Study

New Zealand Transport Agency Study

Sometimes the realities of running a road network don’t match the theoretical world of test standards and regulatory ideals. The competing needs of various infrastructure providers can lead to conflict and compromises are required. The New Zealand Transport Agency found themselves in such a bind and sought our help in solving an operational problem – is it safe to place a street lighting system within the clear zone behind a wire rope barrier without endangering road users?

New Zealand Transport Agency Study

Tasked with optimising the use of space on New Zealand’s road network the New Zealand Transport Agency (NZTA) sought our expertise for a theoretical investigation - what happens when you put a street light too close to a wire rope safety barrier and a vehicle hits the barrier? Will the occupants still be safe? Will the barrier still work properly? What happens to the street light?

The severity of the situation was determined by creating a non-linear large displacement simulation model. The various sub-components of the model were calibrated against actual crash test data helping to improve the accuracy of the simulation. A range of simulations were performed for two vehicle types; a Toyota Starlet and a Chevrolet C2500 Pickup with the lighting column located at various offsets behind the barrier and various positions up and downstream from the impact point.

After some complicated statistical analysis, the results were compared against the requirements of NCHRP-350 and EN 1317-2 for effect on occupant safety. The findings showed occupant safety can be maintained even though the interaction between the street light and barrier significantly changes the barrier performance and vehicle behaviour. This finding was crucial in allowing NZTA to maximise the use of space and opt for non-standard street lighting installations while still maintaining public safety.

For more information, please contact Ben Poulter on +64 3 363 2180 or email BenP@holmessolutions.com.

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Did you know?

  • The energy released when a vehicle impacts a road barrier is proportional to the square of the vehicle speed. As the add on TV says, the faster you go the bigger the mess.
  • An 8000 kg truck impacting a barrier at an angle of 15 degrees with an impact speed of 80 km/hr has less impact energy than a 2270 kg vehicle impacting the barrier at 20 degrees with a speed of 100 km/h.