Exploration of the traffic flow impacts of combined lateral and longitudinal support

1. Exploration of the traffic flow impacts of combined lateral and longitudinal support Bart van Arem (TNO Inro) & Govert Schermers (AVV) Jaarbeurs, Utrecht, December 2003

2. Motivation • Increase knowledge of risk and success factors for deploying lateral control systems • Traffic flow and safety • Acceptance • Infrastructure consequences • Other developments • Increase awareness and acceptance of ADA systems in general

3. Approach • Field Operational test with LDWA • Test fleet • Driving simulator • Acceptance • Infrastructure • Traffic flow • Qualitative exploration • Lateral (LDWA and LKS) • Longitudinal (ACC and ACC+) • Traffic flow simulation • Effects of implementing CA in HGV sector

4. Questions • Potential impacts of lateral support on capacity • What degree of support? • Additional impact of combination with longitudinal support? • Compensate capacity decrease on narrow lanes? • Impact in relation to other in-car devices such as phones?

5. Literature • Workload and attention theory – lower workload creates compensating behaviour, possibly non driving related causing a decrease in driving performance • Little on capacity, driving performance and lateral support • Results of the impact of mobile phone use on driving ambiguous • Longitudinal support decreases workload (but will the driver compensate or relax?)

6. Qualitative traffic modelStructures the relationship between driving behaviour and flow effectshelps experts recognise effects of combinations

7. Expert consultation • Individual polling on hypotheses on parts of traffic model • Workshop discussion of hypotheses in relation to literature • Synthesis of hypotheses into impacts on capacity

8. Reference cases Capacity 6600 veh/h, with 20% heavy vehicles Capacity 6400 veh/h, with 20% heavy vehicles

9. A priori polling: capacity impacts • Impacts LKS stronger than LDWA • Impact stronger on narrow lanes • ACC dominant impact • No additional impact by combination of lateral and longitudinal

10. Reduction of workload • Only in case of active support • Consumers • Few • Degraded driving performance; less lane changes, longer reaction time; more perception errors • Active compensation: • Smaller headways • Use narrow lanes more often

11. Lane change behaviour • ACC, ACC+, LKS: decreased lane changes ‘enjoy the ride’ • Fewer lane changes: positive for capacity • Long platoon: possibly negative • LKS and narrow lanes: increased utilization of narrow lanes

12. Lateral position choice and passing behaviour • Improved passing opportunities; decrease of ‘locking’ on narrow lanes • Lack of preview: potentially unstable traffic

13. Intended speed and headway • No impact of changes in intended speed on capacity • LKS compensated by short headway • Larger headways of ACC/ACC+ lead to capacity decrease

14. Other • Penetration level: • Negative impact at low penetration • Positive impact at high penetration

15. Capacity estimates after workshop

16. Summary capacity effects • Impact LDWA on traffic performance limited • Decrease in workload with more active forms of driver support is enjoyed or compensated ® • Traffic performance depends differently on enjoyers and compensators, in terms of headways, lane changing, reaction times ® • Impacts of lateral support is stronger on narrow lanes