Landmarks
Landmarks are frequently cited during the ad hoc provision of directions. Combined with directional instructions such as “turn right”, landmarks can ease route-following by indicating when and where these actions should be taken. The omnipresence of landmarks within the natural driving environment means that they are ideal candidates to aid the task of navigating when driving in unfamiliar areas and can also provide reassurance when travelling through familiar areas (Burnett et al., 2001). There has therefore been significant research interest regarding the inclusion of landmarks as navigational cues within in-vehicle navigation systems (IVNS). This research has consistently demonstrated that augmenting navigation systems with landmarks improves their usability and utility, and aids route-following. For example, in comparison with conventional distance-to-turn systems, the addition of landmark cues has been shown to improve navigation performance, significantly reducing navigational decision time and errors (Phillips, 1999; May and Ross, 2006). The use of landmarks within route guidance also reduces the frequency of glances to an in-vehicle display, thereby reducing eyes-off-road time (May and Ross, 2006; Phillips, 1999), and has been shown to improve engagement with the environment and promote enhanced spatial learning (May et al., 2005; Leshed et al., 2008). Additionally, improvements in driving performance and increases in driver confidence have been highlighted when using landmark-enhanced IVNS to navigate, and this can lead to reduced reliance on the technology, compared with conventional presentations of route advice (Burnett et al., 2001; May and Ross, 2006).
However, defining what makes a good landmark for navigational purposes can be difficult. Part of the difficulty of selecting suitable candidates lies in the fact that, although some features that make a landmark good for navigation are quantifiable (e.g. advance visibility, spatial extent and permanence), many others have a subjective element (such as semantic salience, uniqueness and usefulness of location) and can therefore only be ‘quantified’ in a specific context (Burnett et al., 2001, May et al., 2005). A common consensus is that ‘good’ navigational landmarks should be permanent (in form and labelling), easily visible, unique, have a useful location, and be easily identifiable. Examples of ‘good’ landmarks may therefore include: traffic-lights, petrol stations, public houses, churches, schools and railway stations (Burnett et al., 2001). Nevertheless, in certain situations, such landmarks may be of limited value for navigational purposes. For example, a distinctive building may be obscured by summer vegetation making it indistinguishable, or several sets of traffic-lights may exist in close proximity to each other making them difficult to differentiate by drivers (Burnett et al., 2001). Further difficulty can exist in selecting and identifying the most appropriate landmark in complex, or high density urban road networks, when numerous ‘good’ candidates may be present, and, while some areas may have an abundance of good landmarks, other areas may be void of suitable candidates.