Estimation of intersection turning movements is one of the key inputs required for a variety of transportation analysis, including intersection geometric design, signal timing design, traffic impact assessment, and transportation planning. Conventional approaches that use manual techniques for estimation of turning movements are insensitive to congestion. The drawbacks of the manual techniques can be amended by integrating a network traffic model with a computation procedure capable of estimating turning movements from a set of link traffic counts and intersection turning movement counts. This study proposes using the path flow estimator, originally used to estimate path flows (hence origin-destination flows), to derive not only complete link flows, but also turning movements for the whole road network given some counts at selected roads and intersections. Two case studies using actual traffic counts are used to demonstrate the proposed intersection turning movement estimation procedure. Figure 5. Estimated (Observed) turning movements for arterial network (RMSE turn ¼ 209.048). A. CHEN ET AL.especially when the turn penalties at intersection are likely to be mis-specified. The observed (in parenthesis) and estimated turning movement flows are shown in Figure 5 for comparison.
St. Helena networkThe City of St. Helena is located in the famous wine-producing region of Napa Valley in California, approximately 65 miles north of San Francisco. St. Helena is a full service City with a population of 6,019 (as of January 1, 2002) within an area of 4 square miles. The City's development pattern is relatively compact, with commercial development and wineries concentrated along Highway 29 (Main Street) corridor, and residential development radiating out from Main Street (see Figure 6).Link volumes collected during the evening peak hour, the time of day when traffic congestion on Highway 29 presents a serious issue, were assembled and a network with 28 TAZs was coded with the observed link volumes. The network contains 113 links and 54 of the links do not have traffic count data. Turn penalties, based on the actual traffic conditions, were also coded with the network such that the shortest paths among TAZ centroids replicate actual travel patterns in the area. PFE was applied to the network for estimation of the O-D table as well as turning movements.For this set of experiments, link counts were aggregated from turning movement counts. As a result, there are link counts on all approaches (both in-bounds and out-bounds) of each intersection. In addition, turning movement counts at two intersections (Fulton/Main and Mitchell Dr./Oak Avenue) were also considered to assist the estimation (used as constraints in addition to link observation constraints). The following three sets of traffic counts were used for the estimations.1. Link counts only (Base case). 2. Base case plus turning counts at Fulton/Main (Option A). 3. Option A plus turning counts at Mitchell Dr./Oak Avenue (Option B). Figure 6. Topology of St. Helena network an...