Bart van Arem (TNO Inro) presented the slides that were made by Govert Schermers (AVV) for the AIDA Seminar. The subject of the presentation was the research undertaken to explore the traffic flow impacts of combined lateral and longitudinal support. The research was undertaken in order to increase the knowledge of risk and success factors for longitudinal and lateral control systems and to increase the awareness and acceptance of advanced driver application systems in general.

The total research consisted of several studies:


A field operational test with a lane departure warning assistant (LDWA);


Qualitative exploration for longitudinal (LDWA and LKS (lane keeping system)) and lateral support (ACC (adaptive cruise control));


Traffic flow simulation.

In the presentation only the qualitative exploration is further elaborated, mainly on the field of impacts of lateral support on capacity. First of all a literature study was undertaken. The results showed that there is an influence on workload and attention of the driver. A lower workload might be compensated by other activities, thus causing a decrease in driving performance. Looking at the influence on capacity, not much literature was found.

In the following step a number of experts was consulted to create hypotheses of the impacts of lateral and longitudinal support. In order to help the experts a qualitative traffic model was made, which described the decisions made by drivers and the input to define capacity. The experts were first individually asked their opinions and later they were put together to define the impacts. For the consultation two reference cases were used; the normal situation (considering lane width) and another situation with another cross-section (narrower lanes).

At first instance the experts thought the impacts of LKS stronger than LDWA and the impact again was stronger on narrower lanes, but ACC was mentioned to have the most dominant impact on capacity. The combination of both lateral and longitudinal support was thought not give any extra impacts. Several elements were described in more detail:


A reduction of workload was only thought of happening in the case of active support, possibly causing a degraded driving performance. Active compensation should be used instead to have a positive impact on capacity.


A decrease in number of lane changes was expected to happen when using ACC or LKS, causing a positive impact on capacity.


The use of LKS was expected to increase the passing opportunities.


No effect was expected for the intended speed but when using ACC with rather large headways could have a negative impact on capacity.

After the workshop with the experts the difference between the experts decreased. The effects of LDWA overall decreased compared to the previous test, but the effects of LKS increased. The combination of ACC and LKS was thought of having the biggest impact on capacity.

The conclusions of the research were thus that a LDWA had limited impact on traffic performance, combined with a decrease in workload.

After the presentation several questions were posed. Regarding traffic safety and incidents it can be mentioned that it was not specifically targeted in this research, mainly because of problems describing the impacts of incidents. Regarding traffic safety it was mentioned that there is trade-off between safety and capacity; both cannot be increased when using LDWA and ACC to create a stable traffic stream, because of the rather large headways used by the ACC, causing a decrease in short term capacity. But the stable stream is bound to cause fewer accidents, thus increasing the long-term capacity. But this has never been investigated in the research. Another problem mentioned was the sensitivity of a LKS. On narrow lanes such a system will give more warnings thus decreasing the probability a driver will use that lane. This will cause a negative impact on capacity. In the research such sensitivity was not used; the systems were thought to be perfect. A final question, which applies to all advanced driver applications is that it is necessary to find a way to increase the awareness of drivers using systems like ACC and LKS.

Click here for the slides of the presentation.