The Stopping Sight Distance (SSD) values calculated by this program are based on the recommendations of Chapter 10 of Manual for Streets 2 (available here), which is published by CIHT and is endorsed by the Department for Transport. The SSD values take into account the measured or design speed of traffic and the gradient of the highway. They assume driver reaction times and vehicle deceleration values based on the design speed and the type of vehicle.
Designers are advised by MfS2 that the Y distance of priority junction visibility splays should be based on these values. However, based on research carried out by TMS Consultancy for MfS2, unless there is local evidence to the contrary, a reduction in visibility below these recommended levels will not necessarily lead to a problem (see MfS2, 10.5.9).
Designers are also advised by MfS2 that forward visibility along highway links should meet these recommended values. However, there will be situations in locations with design speeds of 60kph or less where it is desirable and appropriate to restrict forward visibility to help control traffic speed. (see MfS2 10.3.2)
PJA has endeavoured to ensure the accuracy of this program. However, the guidance and recommendations given by the program should always be received by the reader ‘in light of the facts’ of their specific circumstances and other specialist advice obtained as necessary. Any references to legislation discussed within this program should be considered in the light of current and any future legislation. No liability for negligence or otherwise in relation to this program and its contents will be accepted by PJA.