A Comprehensive HCM 2010 Urban Streets Analysis Using HCS 2010 US 31W in Elizabethtown, KY Ashley McLain, PE, PTOE Abstract The HCS 2010 Streets module was used to analyze a segment of the US 31W corridor in Hardin County, Kentucky. The area of analysis spans 9.5 miles and includes 19 signalized intersections. A multiple-period analysis (six-15 minute periods between 4:00 PM and 5:30 PM) was used to account for unmet demand during the oversaturated PM peak period. Additionally, the HCS Streets module allows the impact that access points have on thru traffic to be considered in the analysis. Trip generation data was used to estimate traffic at these unsignalized access points throughout the corridor. Data was collected during site visits to the corridor for use in calibrating the model. The results produced using the HCS Streets module were compared to observations made and data obtained during site visits. Overall northbound and southbound travel times in addition to travel times measured between intersections, queue lengths, and average speeds throughout the corridor were the measures of effectiveness used to ensure the model was calibrated to existing field-measured conditions. The HCS 2010 Streets analysis accurately modeled the existing baseline conditions throughout the PM Peak of the US 31W Corridor. Key factors in obtaining a calibrated model included field calculation of saturation flow rate, obtaining existing signal timing files, and using the multiple-period analysis capabilities available in HCS. Introduction US 31W in Hardin County, Kentucky, is a heavily traveled corridor connecting the cities of Elizabethtown and Radcliff. The corridor analyzed in this study spans 9.5 miles and extends from the US 31W Bypass in Elizabethtown to the Wilson Road Overpass in Radcliff. This segment is heavily congested during the PM peak period and serves as a primary route for Fort Knox traffic. The corridor includes 19 signalized intersections and numerous unsignalized access points. The typical section varies between a four- and five-lane section with turn lanes throughout the study area. Due to the high number of crashes throughout the project limits, and increasing congestion, the Kentucky Transportation Cabinet (KYTC) selected Palmer Engineering to perform a study for implementing Access Management and to develop construction plans for improvements along US 31W. With the recent publication of the 2010 Highway Capacity Manual, Palmer Engineering and the KYTC identified the US 31W project as one of two beta testing projects in which to use the new Urban Streets Analysis module. The Urban Streets methodology allows for analysis of multiple signalized intersections throughout a corridor, while taking into account the effect of access points on the flow of traffic. The Urban Streets
methodology also has the capability to analyze multimodal operations, although this specific feature was not used on this project. Palmer Engineering worked with the McTrans Center at the University of Florida, developer of the Highway Capacity Software (HCS), to use the 2010 HCS Streets module for operational analysis of the US 31W Corridor. At the time the project began, the HCS Streets module was still untested on a large scale project. The KYTC and Palmer Engineering thus elected to perform the HCS Streets analysis in conjunction with CORSIM microsimulation for results comparison. The purpose of this paper is to document the results provided by HCS Streets in comparison with existing field conditions throughout the US 31W corridor. Initial Data Collection The KYTC provided 15-minute PM peak-hour turning movements between 4:00 PM and 5:30 PM for each of the 19 signalized intersections along this segment of US 31W. Signal timing reports for each intersection were provided by the KYTC. The intersections included both coordinated and uncoordinated signal systems. Palmer Engineering began developing the Existing 2012 HCS Streets file with the turning movements and signal timing information provided. The program s ability to input multiple periods of data was used. McTrans advises that using a multiple-period analysis allows unmet demand of a preceding period to be accounted for in the following period under oversaturated conditions. The residual queues for each period are used as the initial queues for the subsequent period, allowing for a more accurate computation of delay for the overall analysis 1. Six 15-minute periods of data were input into the US 31W corridor HCS Streets file. Aerial mapping was used to determine lane widths, lane configurations, and storage lengths. Google Earth was used to verify signal heads, lengths of restrictive medians, presence of curb, and number of access points. The information obtained from aerial mapping and Google Earth was verified and updated as needed, following visits to the project site. The HCS Streets module allows the effect of unsignalized access points on corridor traffic to be considered. This segment of the US 31W corridor has a total of 393 unsignalized access points throughout the project limits. The effect of these access points was taken into account with the number of right-hand access points and the midsegment delay. Mid-segment delay (delay to thru vehicles due to vehicles turning into an access point) 2 was estimated for each segment using the method outlined in the 2010 Highway Capacity Manual. Representative values for mid-segment volume, number of thru lanes, and the percentage of left- and right-turn lanes for each roadway segment were used to estimate thru-vehicle delay. The 393 unsignalized access points were then combined into 53 active access points. The general rule of thumb suggested in the 2010 Highway Capacity Manual is that an access point is considered active if it has an entering flow rate of 10 vehicles per hour or more during the analysis period 3. Additionally, if several inactive access points in a segment collectively have an impact on traffic flow, the inactive access points can be
combined to form a representative active access point(s). For each of the active access points, HCS Streets allows users to enter turning movements and lane allocations. Due to the high number of unsignalized access points, Palmer Engineering determined it was not feasible to do turning movement counts at each intersection during the peak period. Instead, the land usage and building sizes throughout the corridor were analyzed and peak hour trips were estimated using the ITE Trip Generation Manual. These trips were then distributed to the corridor based on existing distribution patterns. During a visit to the field, access point volumes were spot checked to ensure trips generated by the developments were reasonable for the corridor. Field Visit Several key pieces of information were obtained from field visits. In addition to verifying data from aerial mapping and Google Earth, the following information was gathered at the field visits: Corridor Length Northbound and Southbound Travel Times in PM Peak Observation of Queuing throughout Corridor in PM Peak Saturation Flow Rate Calculations Observation of Speeds Traveled in PM Peak Volume Surveys at Representative Access Points throughout Corridor The method outlined in the 2010 Highway Capacity Manual was used to measure the local saturation flow rate throughout the corridor. Representative intersections were selected throughout the corridor for field measurements of saturation headway per vehicle. The project beginning is located approximately one mile north of the KYTC s District 4 office in Elizabethtown. District 4 provided multiple sets of BlackStar data to Palmer Engineering during the PM peak hour. BlackStar is an application used in conjunction with a BlackBerry phone that provides GPS data. Using Google Earth, Palmer Engineering extracted multiple sets of travel time and speed information from the BlackStar data to use for model verification and calibration. Model Verification and Calibration Much of the data needed for calibration had been collected and entered prior to field visits. Measuring saturation headway in the field for calculation of the saturation flow rate was a key element of the calibration process. The HCS Streets default saturation flow rate of 1900 passenger cars per hour per lane was compared to the saturation flow rate calculated throughout this segment of the US 31W corridor of 1750 passenger cars per hour per lane. Changing the saturation flow rate allowed for local driver characteristics to be considered. During the field visit, travel times were obtained for the overall corridor in both the northbound and southbound directions. Additionally, travel times were recorded in each direction between signalized intersections to allow for model verification throughout the
entire corridor. Travel times between intersections were largely dependent upon which signals stopped traffic. Once all data gathered from field visits were included in the model, the output results were compared to the existing field conditions. Results The peak hour data was selected from the six 15-minute periods of data that were input into the HCS Streets file. Figures 1 and 2 show the travel time results. The southbound US 31W corridor field travel time was 20 minutes and 58 seconds. The HCS Streets analysis yielded an overall southbound travel time of 20 minutes and 36 seconds. Figure 1 illustrates the travel time calibration results between intersections in the southbound direction. 25 Travel Times Southbound US 31W Corridor 20 Travel Time (Minutes) 15 10 5 HCS Streets Field Measured 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Intersection Figure 1: Southbound Travel Times along US 31W Corridor The overall southbound US 31W HCS Streets travel time is within 2% of field measurements.
The northbound US 31W corridor field travel time was 18 minutes and 35 seconds. The HCS Streets analysis yielded an overall northbound travel time of 19 minutes and 40 seconds. Figure 2 illustrates the travel time calibration results between intersections in the northbound direction. 25 Travel Times Northbound US 31W Corridor Travel Time (Minutes) 20 15 10 5 HCS Streets Field Measured 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Intersection Figure 2: Northbound Travel Times along US 31W Corridor The overall northbound US 31W HCS Streets travel time was within 6% of field measurements. The average speed between segments and the back of queue results were also reviewed from the HCS Streets file. The results were found to be consistent with observations in the field. Conclusion Because of its limited use at the time this project began, the study for Operational Improvements for the US 31W was used as one of two beta testing projects in Kentucky that tested the applicability and results of the HCS 2010 Streets module. A second project, US 25 in Laurel County, Kentucky also was used as a beta testing project for the HCS 2010 Streets module. Results from this project have been similar to observations for US 31W in Hardin County. Results obtained from the HCS Streets analyses have shown that the Urban Streets methodology accurately modeled the existing baseline conditions. The key factors in calibrating the model to field conditions included obtaining existing signal timing data from KYTC, calculating saturation flow rate in the field, and using the multiple-period analysis to reflect delay due to unmet demand throughout the corridor.
Author Information: Ashley McLain, PE, PTOE Project Engineer Palmer Engineering Company 400 Shoppers Drive Winchester, KY 40391 Phone: 859-744-1218 Fax: 859-744-1266 Email: amclain@palmernet.com References 1 HCS 2010 Tips and Frequently Asked Questions. HCS 2010. McTrans Center, University of Florida, 1 Feb. 2013. <http://mctrans.ce.ufl.edu/hcs/faq/> 2 Transportation Reseach Board, HCM 2010: Highway Capacity Manual, Volume 3, National Research Council, Washington DC, USA, 2010, Page 17-35. 3 Transportation Reseach Board, HCM 2010: Highway Capacity Manual, Volume 3, National Research Council, Washington DC, USA, 2010, Page 17-10.