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So there has been basically no change over the 37 years from 1974 to 2011. A 1974 UK source (ref.167) refers to a figure of 1.05m. The 2011 edition suggests 1.07m and refers to a study from 1997. The AASHTO green book 1994 edition suggests an eye height for car drivers of 1,08m and refers to studies from 1978.

Geometric design guides should give figures for the driver eye height of other vehicle types.ĭriver eye height – consistency over time Obvious examples are bus lanes, cycle tracks and pedestrian footpaths. And of course there are more than just two types of vehicle on most roads, and some parts of the road may be restricted to vehicle types other than cars or trucks. There may be several traffic lanes, and sight distance should be checked for each of them, over a range of values which create a “box” shape. This also gives us the idea of a range of values and a minimum value.Īn envelope is a two-dimensional object, but roads are three-dimensional. Design engineers have to test the available sight distance over this range (or envelope) of values. Several standards therefore quote an upper (truck driver) eye height and a lower (car driver) eye height. Here, a truck driver with a higher eye height will more likely have his line of sight line blocked by the bridge. Other references argue that in some circumstances sitting higher can be a disadvantage – for where there is an overhead obstacle on sag vertical curves (e.g. The argument for this is that truck drivers usually sit higher than car drivers and so they can see farther. Some references only quote a single value, the eye height of drivers of cars. Driver eye height is one of the parameters used in checking sight distance (stopping sight distance for example).