Assessing the Benefits and Costs of Intelligent Tranportation Systems: Ramp Meters

This study undertakes an evaluation of the benefits and costs of ramp metering. The primary purpose was to provide empirical information on the value of the introduction and use of this form of ITS technology. Three cases are examined in the analysis. The impact of ramp metering on traffic behavior is simulated based on a cell transmission model and an assumed travel demand on the freeway as well as the ramp. Temporal travel demand change is determined based on the average travel pattern obtained from the I-880 freeway database. Isolated, single traffic responsive ramp metering is assumed. We identify and quantify the benefits and costs based on established assumptions, and finally analyzed economic value of ramp metering. Benefits of ramp metering are derived based on travel time value and fuel consumption and by savings in travel delay. In this study, it turns out that there is a net increase in vehicle emissions as a result of with ramp metering. The costs of ramp metering are site dependent and a function of planned metering technology. Since this study is not for any specific site, costs are estimated for three cases obtained from conversation with traffic engineers at Caltrans District 4 or literature. Under the original assumptions regarding fuel economy, time value and travel demand on the freeway and the ramp, investing in ramp metering generates a NPV of $10.44 million. For all three cost scenarios, ramp metering turns out to be worthwhile implementing – the Benefit-Cost ratios exceed 1 in all cases. To examine the effect of change in some of the assumptions, we conducted sensitivity analysis. Since the original assumptions yield output favorable to ramp metering, we altered the assumptions to reduce the benefits. Specifically we reduce fuel economy but this doesnot make a significant change in benefits (1.6 % of previous total benefits). Since time saving is the major source of benefits, we reduced the time value. This resulted in a reduction in benefits of 26.5 %, however, ramp metering is still worthwhile implementing based on all three measures of B/C ratio, NPV and IRR. Ramp demand is reduced to 50% of previous demand. This reduction in ramp demand results in a reduction in travel demand such that it is less than capacity for the first four years. Therefore the ramp is not metered and does not generate any benefits until after the forth year once the ramp meter is put in place. As well, freeway demand is reduced to 10% of the previous level. This reduction of freeway demand results in a level of travel demand that is less than capacity for the first five years. Sensitivity analysis for different values of capacity reduction is also conducted. Two different cases of capacity reduction are analyzed: 98% and 99% of normal capacity. As a result of the reduction in capacity, the amount of travel delay reduction resulting from ramp metering is reduced by approximately 64% and 31% respectively. However, ramp metering still is worthwhile implementing.