1. 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: km /year
Figure 5 : Number and duration of eye gazes towards VMS
This study was made possible by the NPRP award [NPRP ] 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