Examining the effect of road horizontal alignment on the speed of semi-automated vehicles

Abstract

The novel semi-autonomous vehicles are becoming a reality in our roads, being a very important technological advance with promising operational and safety improvements. However, road infrastructure must be ready to host them. The technologies of these driving automation systems require certain road conditions that are not always fulfilled, causing the systems to fail. These failures generally transfer negotiation control to drivers, which may induce a crash if they were not aware of road and traffic conditions.This research analyses how ready the road horizontal alignment is for existing semi-autonomous systems. A Level 2 vehicle has been tested on many different horizontal curves, finding a strong relationship between the maximum speed that the autonomous system can attain and the curve geometry. This maximum speed is proposed as a new concept (automated speed) and has been found to be lower than the design, operating and posted speeds in many cases. Another new concept – automated driving consistency – arises, as the difference between automated and operating speeds. The related inconsistencies can be addressed with the new concept of Level of Service for Automated Driving (LOSAD), which summarizes how ready a corridor is for a certain driving automation system. This parameter should be determined – further certified – for any homogeneous road segment, and later informed to drivers.