Sight Distance of Automated Vehicle Considering Highway Vertical
Alignments and Its Implications for Speed Limits
Abstract
Most existing road infrastructures were constructed before the emergence
of automated vehicles (AV) without considering their operational needs.
Whether and how AV could safely adapt to as-built highway geometry
remain inconclusive, and a plausible concern is a challenge from
vertical alignments. To fill this gap, this study uses virtual
simulation to investigate the available sight distance (ASD) for AV on
vertical alignments subject to the current highway geometric design
specification, and its implications for speed limits. According to the
scenario generation framework, several scenarios featuring vertical
geometric elements and the light detection and ranging (LiDAR) sensor
were created and tested. Moreover, the maximum speed for adequate ASD is
calculated to determine the AV speed limit, considering safe sight
distance and speed consistency requirements. The results indicate that
crest curves are not disadvantaged in ASD compared with either the sag
curves or tangent grades. Only equipped with multi-channel LiDAR and
advanced perception algorithms enabling a lower detection threshold,
would Level 4 AV be compatible with the as-built vertical alignment with
a design speed (Vd) of 100 km/h. However, Level 3
AV can only adapt to the vertical profile with Vd
= 60 km/h. The findings of this study should be of interest to the
road-oriented operational design domain and support road administrators
in regulating AV safe speeds.