California Partners for Advanced Transportation Technology

This report furnishes clear evidence that on-ramp metering can increase the output flow through a freeway, and by so doing diminish the total time that commuters collectively spend traveling on the freeway and its on-ramps. Empirical study was performed on a 6.3-mile stretch of northbound Interstate 5 in Sacramento. The stretch spans the interchanges of Pocket Road (to the south) to W street (See Figure 1). Traffic data, both from loop detectors and from videos, were collected during the morning rush periods over a period spanning several years. Data were initially collected in 2006 prior to the deployment of ramp meters at the site. Data were collected again in 2007 and 2008 after meters were installed on five on-ramps. (The meters operate using a control logic developed by Caltrans.) Finally, a metering logic was developed in response to certain traffic details observed at the site, and was tested there in spring and fall 2009. A number of interesting and useful findings resulted from all this, as described below.