  This paper evaluates the impact of geometric and operational features on
freeway capacity at merge bottleneck locations, by analyzing pre-breakdown flow
rates and using parametric and non-parametric techniques. These features
include number of lanes, free-flow speed or speed limit, length of acceleration
lane, and presence or ramp metering. The analysis was carried out on seventeen
freeway merge sites across the United States. The number of lanes showed
negative relationship with the per-lane average pre-breakdown flow rate. Sites
equipped with ramp meters also showed higher pre-breakdown flow rates than
unmetered sites. In survival analysis, the number of lanes and presence of ramp
meters were the only features found to have a statistically significant impact
on the survival (or breakdown) probability. Capacities, defined at the flow
rate that corresponds to 15 percent breakdown probability, were 2,048, 1,959,
and 1,745 pc/hr/ln at three-lane, four-lane, and five-lane unmetered sites,
respectively. Capacities were 2,248 pc/hr/ln at three-lane and 2,132 pc/hr/ln
at four-lane metered sites. The effect of acceleration lane length and Free
Flow Speed (FFS) on pre-breakdown flow rate and survival probability was not
found to be significant.
