Arts & Social Sciences
Te Kura Kete Aronui

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  Road Design

Rural/urban threshold design
1999 Masters' Thesis by BD Alley

Rural/urban thresholds are an increasingly common speed change treatment in New Zealand. 
Road Controlling authorities wanted to know why some were effective and others appeared to increase speeds.

The interesting theoretical question was whether thresholds worked by increasing the signs’ attentional conspicuity of increasing drivers’ perceptions of speed?

The findings indicated that thresholds work even without explicit speed restriction information.  The visual characteristics had a perceptual effect due to the increased optic flow in the driver’s visual field.

Thresholds appeared to have an immediate effect on speed commensurate with the size of the signs and degree of visual narrowing due to reductions in lane width.

But, because of VMAE, 250 m after passing a threshold drivers’ speeds return to a level higher than before (unless road and traffic conditions reinforce maintenance of lower speeds.