Restricted Sight Lines

Restricted sight-lines are one of the three methods of speed control used for COMPACT URBAN ROUNDABOUTS

Restricted sight lines can affect driver approach speed to an intersection, and there are examples from both the United Kingdom and New Zealand where sight screens have been installed to positively affect traffic safety in rural areas.  NZTA research in 2012 concluded this method of speed control can be applicable to urban areas, although further experimentation is recommended to more fully develop the concept in practice.



Below is a sight screen previously installed on Paeroa-Tahuna Road at its intersection with State Highway 27 in the North island of New Zealand.  A roundabout has since replaced the hazardous cross-junction, but studies did show the sight screen made a noticeable safety improvement in terms of reducing minor-road driver approach speeds.







Below is an example of a single-lane roundabout with very low central islands, which is quite feasible if speed control is adequately achieved by measures that could include sight line restrictions.  Town centres like this one might experience relatively low vehicle speeds in any case, but low volume periods could be different.  Low or even flush central islands can be beneficial for bus-passenger comfort, as turning buses often have to traverse central island features in confined situations such as these.








Below is a concept for a 25 metre inscribed diameter two-lane Compact Urban Roundabout using restricted sight lines rather than geometric elements for speed control, and narrow lanes for additional capacity. Orange denotes obstacles such as buildings, walls or thick vegetation which obstruct sight lines for all types of vehicles including trucks which have drivers seated high (so 3.0 metres minimum height is recommended).   Very good street lighting is likely to be important, in order to minimise headlight flashes which can give advance warning of oncoming vehicles from the side at night.  The central island would be nominally low or flush with the road surface.

C Rbt 25m-Onehunga Grey SIGHTLINE iC Rbt 25m-Onehunga Grey SL Track i