A Tool to Aid the Comparison of Improvement Projects for the Virginia Department of Transportation
The goal of this effort is to assist the Virginia Department of Transportation (VDOT) in improving the comparison in planning of potential primary and secondary roadway improvement projects. Historical projects that have been implemented or considered for implementation have been used as a case study data set. Methods are proposed for estimating cost, performance gain and crash risk reduction of future roadway projects, with the main focus being the presentation of trade offs among these criteria. If, in a particular case, more accurate and/or appropriate data is available for one or more of these criteria (e.g. from a simulation study that has been performed), then this information can easily be used to supplement or replace the estimations proposed here. The project comparison instrument combines three major decision making attributes in project selection: crash risk, performance, and project cost. By quantifying these attributes across a number of proposed highway improvement projects, projects can more readily be compared to one another, and a more holistic view of potential projects is achieved. This is an important step when choosing a portfolio of projects each year. In order to compare projects, attributes are quantified in the following manner for planning level decisions. Crash risk reduction is calculated as the number of crashes avoided per year at the project site. Particular roadway improvements are typically assumed to decrease the expected number of crashes by a statistically determined and pretabulated percentage. Performance gain is quantified by the vehicle minutes of travel time avoided in the peak hour. Finally, cost is modeled as the sum of preliminary engineering, right of way and construction costs. Once the objectives are quantified, they can be graphically displayed in a Project Comparison Chart. Examples for applying this approach are given in the text and in the accompanying workbook.
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A-type accident occurrence Accident Reduction Factors Accidents Accidents altematives analysis approach ARFs average number B-type beneﬁt Bound Bound calculated chi-square distribution Classiﬁcation concem conﬁdence interval conﬁdence level cost estimates cost overrun countermeasure Crash Risk Assessment crash risk reduction crashes avoided Cumulative Distribution Function database deﬁned deﬁnitions density Department of Transportation developed expected facility fatal ﬁgures ﬁnal report ﬁrst ﬂow rate fractile method Highway Capacity Manual identiﬁed injury lane level of service lower upper measure methodology models number of accidents number of crashes observed number ODOT peak hour performance Poisson distribution predict probable conﬂict ratio reﬂects Review of Existing roadway improvement projects saved per vehicle Selection and Adoption service ﬂow signalized intersections signiﬁcant Six Year Plan speciﬁc Trafﬁc Engineer Transportation Research travel time saved triangular distribution types University of Virginia upper Bound variables VDOT VDOT’s Vehicle minutes volume Wattleworth Workbook