The goal of the Automated Highway System (AHS) is to blend engineering ingenuity and technology to produce a new level of transportation services. Human factors are difficult to integrate with AHS design because they represent a variety of training, experience, skills, and goals. Human factor considerations are essential for AHS design because humans will be involved in automated driving. For instance, drivers may be expected to instruct their vehicles to exit locations, input parameters such as speed and desired headway, or take control in some emergency situations. The tasks that human drivers will be expected to execute have not yet been fully defined. One human factor dilemma that AHS engineers might face is that if human drivers are not allowed to intervene in the vehicle control process during malfunction and emergency situations, they may be trapped in a system with high failure rates. This could result in public distrust and a lack of public will to deploy an AHS. However, if drivers are allowed to take control of their vehicles at will, some may intervene at inappropriate times, causing a potential system failure. A framework has been developed for evaluating human factor concerns for automated vehicle control. These concerns involve basic driving tasks: ( a) detection, ( b) recognition, ( c) situation analysis, ( d) decision making, and ( e) control response. An analytical process to determine the responsibilities of the human driver, vehicle, and AHS infrastructure for these driving tasks is presented.
The automated highway system (AHS) concept with dedicated lanes is not designed as a stand-alone transportation facility. Drivers will by necessity need to drive from their origins to the AHS entrance and from the AHS exit to their final destinations. Therefore, the AHS will affect other transportation facilities and will need to be integrated with all other facilities in the transportation system. Interfaces create much of the congestion for today’s transportation systems. AHS interfaces may cause similar problems, as a result of either AHS interactions with conventional systems or internal limitations from AHS merging capabilities. If these problems exist, either the AHS or the conventional road network cannot function properly. Then the system as a whole will break down, and the AHS could prove a detriment to the overall transportation system. Clearly not enough is known about the automated merging process to determine what conditions would lead to congestion at interface points. Current macroscopic techniques assume parameters that are not applicable to an AHS, and no detailed AHS merging models have been developed and validated. The AHS to conventional roadway interface problem is addressed by presenting a microscopic simulation model for one scenario of the automated merging maneuver. Some numerical results are presented for this merging scenario.
Special connector ramps linking the automated lanes at automated highway–to–automated highway interchanges may be needed to enable continuous automated driving between two crossing highways. Although a typical cloverleaf configuration has only two levels and is more amenable for such additions, the sharp curvature of this design usually imposes constraints on traffic speed and flow. Because of these constraints, most highway–to–highway interchanges in urban areas have straighter lanes but tend to involve three or more levels. Building the additional connector ramps to accommodate eight high-speed turning movements at an area where the geometry is already complex could be difficult or costly. Therefore, proponents of automated highway systems (AHS) face a major dilemma. This dilemma is studied, including the impact of not providing automated connector ramps on the manual and AHS traffic on manual lanes at or near a highway-to-highway interchange. It is shown that, with a typical cloverleaf design, in the absence of the additional connector ramps, any moderate to heavy AHS-changing traffic could severely disturb the flow of through traffic, seriously exacerbate congestion, and possibly cause a traffic breakdown at the interchange area. These effects will most likely negate any mainline throughput benefits for which an AHS is designed.
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