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U.S. Department of Transportation
Variable Speed Limit (VSL) Systems
and
Speed Reductions
Speed Reductions
§Variable Sped Limit (VSL)
Systems
□Collect traffic data using
traffic sensors and post speed limits that harmonize traffic flow using dynamic speed signs.
□Account for traffic
conditions, weather conditions, time of day, traffic incidents and lane
closures.
□Reduce congestion, provide more
reliable journey times, reduce the frequency of accidents, reduce carbon emissions, and
reduce driver stress.
§Speed Reductions
□Research from the University of Texas at
Austin found that reducing speed limits on a freeway from 65 mph to 55 mph on a “Code Red Air Quality Day” resulted in a 17%
reduction in NOx over a 24 hour period.
□Graz, the second largest
city in Austria,
reduced speed limits
from 50 kph (31 mph) to 30 kph (19 mph) for the entire city area. During the two-year trial, NOx emissions
were reduced by 25%.
Source: The A14 Alternative
Source: FHWA Office of International Program