Safety Impacts of Freeway Managed-Lane Strategy

This paper presents results of a safety analysis of a freeway managed-lane strategy, that is, a time-of-day managed-lane strategy that concurrently allows use of the inner left lanes by high-occupancy vehicles (HOVs) and use of right shoulders as general purpose travel lanes during peak hours. Recent 3-year crash data and corresponding annual average daily traffic (AADT) volumes and lane-type-specific AADT volumes were identified for various lane types, including the inner left lanes for HOV only use during peak hours, general purpose lanes, right shoulder lanes, and all lanes as a whole. Negative binomial regression models were used to estimate the effect of this traffic operations system and other factors relevant to crash frequency. The negative binomial regression model analyses present no evidence that the interest factors, including the managed-lane strategy during peak hours, AADT volumes, merging and diverging influence areas, weather, light conditions, and existence of pull-off areas, affect the crash frequency when aggregated across all lanes. The variable AADT volumes in the specific analysis of general purpose lanes appear to be significant and show about a 2% increase in weekday crashes for each increase of 1,000 vehicles per day in the AADT range of 50,000 to 83,000 vehicles per day. Right shoulder specific analysis shows that motorist behaviors at the merge and diverge areas during adverse light conditions are significant and shows an increase of about 38% in crashes in these areas. The managed-lane strategy does not appear to be significant to the crash frequency in the inner left lanes for HOV, general purpose lanes, or right shoulders.