IU: Discriminating between more than 2 information units on a VMS ( condition E) generates increased mental workload resulting in more/longer gazes. Variable Message Sign strategies for congestion warning on motorways – A driving simulator study Nora Reinolsmann, Wael Alhajyaseen, Kris Brijs, Tom Brijs, Joris Cornu, Kristof Mollu Introduction Driving scenarios Designs & distances are derived from available guidelines (e.g. European EasyWay II, Federal Highway Administration) & empirical studies VMS formats were selected in consultation with Dynamic Traffic Management Unit of the Flemish Traffic Centre) Severe rear-end crashes due to unexpected hard congestion tails on motorways Hard congestion tail (i.e., drivers brake hard due to unexpected congestion tail Soft congestion tail (i.e., traffic slows down gradually due to emerging congestion) Advance warning of hard congestion tails to enable driver’s to gradually lower speed and avoid erratic maneuvers/ accidents. Figure 6 : Mean deceleration in condition B (1km) Drivers start to slow down at 460m before the congestion tail with max. deceleration -2.3m/s2 Table 1: Test conditions in the driving simulator Objective: How to convey an advance congestion warning in the most effective way using Variable Message Signs? Variable Message Signs Figure 7 : Mean deceleration in condition C (2km) Drivers slow down at 300m before the congestion tail with max. deceleration -2.8m/s2 VMS types: gantry (overhead sign) vs. cantilever (rode side pole) Distance VMS location to congestion tail: Tactical distances: 1km vs. 2km (standard) vs. 4km Strategic distances: 5-10km 3. Message design: Layout (pictogram with or without text) Number of information units (2 to 4 units) Distance indication to congestion tail Discussion Results VMS type: Gantry panels best visible for drivers on all lanes Information units: More than 2 IU on a VMS (condition E) generates increased mental workload  more/longer eye glances The distance to the congestion tail itself is more important than VMS distance indication VMS distance of 4km & more is contra-productive Accidents One collision avoidance maneuver (condition D) 6 drivers had a rear-end accident (all conditions, except for B & C) Mean speed Conclusion A gantry-mounted congestion warning displaying a pictogram with the word ‘congestion’ at 1km before the congestion tail.  Lowest speed, smooth deceleration & safe stopping distances The effectiveness of a congestion warning on VMS is dependent upon: message visibility from all lanes message-incident contingency  link with the critical event warned for Figure 3 : Mean speed Figure 1 : example of a gantry (left) & cantilever (right) Lowest initial mean speeds of drivers approaching the congestion tail were found in condition B Methodology Mean deceleration Driving simulator Medium-fidelity fixed-base simulator (STISIM M400) 180° screen with a resolution of 1,024 × 768 pixels at a 60 Hz refresh rate. Eye tracker: FaceLAB 5.0 for eye movements Recommendations Gantry sign is preferred over cantilevers to display a congestion warning Tactical congestion warning at a standard distance of 1km instead of 2km Use a pictogram with text unit “congestion” Figure 4 : Mean deceleration Condition B: safer stopping distances due to a more gradual and smooth deceleration among drivers Gaze parameters Limitations & future research Follow-up studies with larger sample sizes & more test scenarios Types of distraction leading to longer reaction and response times On-road studies for absolute validity Figure 2 : Driving simulator at Transportation Research Institute (IMOB Belgium) Participants Acknowledgement 43 Belgian drivers (~ 43 age) with a valid driving license Driving experience: 10.000 -14.999km /year Figure 5 : Number and duration of eye gazes towards VMS This study was made possible by the NPRP award [NPRP 9-360- 2-150] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the author[s]. Gantry-mounted VMS (B-E): slightly higher number of eye fixations with a shorter gaze duration