Dual turn slip lanes across pedestrian crossing locations are a well-known higher risk configuration. The issue is visibility.
In these layouts, the lead vehicle can mask pedestrians, signals, and signs. The following driver is managing multiple tasks in a short space and time, often at higher speeds, while critical information is partially or fully hidden.
When a driver proceeds through on a red signal, it is often framed as simple non-compliance. However, if key information is masked, missed detections should not be unexpected.
Key risk factors include:
- Dynamic visual obstruction between vehicles
- Reduced sight lines to pedestrians
- Higher approach speeds
- High task complexity at the decision point
A Safe System approach focuses how we can design this out of the system and how we can lessen the severity of any that still occur.
Potential responses include:
- Raised crossings to reduce speed and reinforce the crossing point
- Repositioning crossings to improve visibility
- Reducing to a single slip lane to remove masking (makes for fun discussions with the traffic operations team)
- Tightening geometry to slow movements
- Reviewing signal control and separation
If the design allows critical information to be hidden, errors should be expected and need to be managed.
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