Evaluating Alternative Operations Strategies to Improve Travel Time ...

SHRP 2 L11: Final Appendices
Strategy: 5.5. Variable Speed Limits (VSL)
Category: 5. Infrastructure Improvements and Optimization
TREATMENTS AND IMPACTS:
Variable Speed Limits (VSL)
• Safety: VSL in England supplemented with automated speed enforcement have reduced rear-end crashes on approaches to freeway
queues by 25 to 30 percent (5).
Multi-year evaluation of VSL impact on traffic safety indicates a reduction in accident numbers by as much 20% to 30% after VSL
installation (6).
VSL (a.k.a speed harmonization in Europe) in the A5 motorway in German was attributed with 3% reduction in crashes with light
property damages, 27% reduction in crashes with heavy material damage, and a 30% reduction in personal injury crashes (25).
In Netherlands, VSL has reduced collisions by about 16% (25).
• Mobility: A road weather information system with variable speed limit signs in Finland was projected to decrease the average
vehicle speed by 0.4 to 1.4 percent and reduce the annual crash rate by 8 to 25 percent (1).
The use of variable speed limits with distributed traffic signal controllers were shown to reduce bottlenecks by 20% (4).
A VSL system in Copenhagen, Denmark reduced mean vehicle speeds by up to five km/h and contributed to smoother traffic flow
(5).
The analysis of a European motorway equipped with VSL and controlled algorithms thresholds showed that critical occupancy is
shifted to higher levels, enabling higher flows (6).
A simulation study on I-4 segment in Orlando revealed a reduction of up to 21% in travel time when VSL is used together with
ramp metering systems (13).
Simulation study on I-66 and I-95 Northern Virginia showed that VSL together with Hard Shoulder resulted in travel time savings
of up to 7 min per vehicle (16).
In Netherlands, VSL implementation has increased throughput 3% to 5% and reduced the cost of work zone traffic control (25).
A study in Germany found that VSL could increase the total capacity of a freeway by 10% (34).
• Efficiency: A VSL system in Copenhagen, Denmark reduced mean vehicle speeds by up to five km/h and contributed to smoother
traffic flow (5).
ADDITIONAL DESCRIPTION AND QUANTITATIVE BENEFITS OF TRAVEL-TIME RELIABILITY STRATEGIES Page F-41