Seckin Ozkul

Revised Version of the Automobile Level-of-Service Methodology for Urban Streets in the Highway Capacity Manual 2010

The Highway Capacity Manual 2010 (HCM 2010) contains a significantly revised automobile analysis and level-of-service (LOS) methodology for arterials. This study compared the arterial LOS results of the HCM 2000 and HCM 2010 methodologies for an experimental set of arterial segments and analyzed the effects of the revised methodology. In addition, existing Florida field data sets were also analyzed with arterial segments obtained from Gainesville, Tallahassee, and Tampa, all in Florida, as well as data received from the Florida Department of Transportation Districts 2 and 3. The HCM 2010 results showed that for shorter, lower-speed arterial segments [such as in central business districts (CBDs)] it was not possible to obtain LOS Ratings A or B. Therefore, many CBD arterials that had good LOS values under the HCM 2000 methodology would now have moderate to poor LOS values. Consequently, the research team tested several revisions of the HCM 2010 methodology to find an approach that would not be as punitive to arterials with shorter segment lengths and that would provide a good balance of LOS values across a range of segment lengths, posted speeds, and traffic demands. Suggested revisions to the HCM 2010 methodology that allowed this objective to be achieved consisted of the following: the use of two classes instead of one (on the basis of the posted speed); the use of the average travel speed as the service measure instead of the ratio of the average travel speed to the base free-flow speed; and the setting of the free-flow speed to equal the posted speed plus 5 mph, instead of using the free-flow speed computations in the HCM 2010 methodology.

Evaluation on the Perceived Effectiveness of Red RRFB Configurations to Reduce Wrong-Way Driving

Despite providing the necessary required signage and pavement markings as per the Manual on Uniform Traffic Control Devices (MUTCD), wrong-way entries onto freeway and limited access facilities continue to occur and lead to wrong-way crashes, which can be severe and even fatal. Yellow rectangular rapid flashing beacons (RRFBs) have been proven to be effective to alert drivers to yield to pedestrians crossing streets; however, the effectiveness of red RRFBs with specific configurations installed at freeway off-ramps on reducing wrong-way driving onto freeway mainlines were unknown. This research investigated various combinations of RRFBs and wrong-way signs and their location placement to determine the RRFB combination most preferred by the motoring public for implementation and to assess their perceived effectiveness via a detailed public opinion survey. Comprehensive analyses were conducted based on 296 participants’ answers to a series of survey questions after their reviews of field videos recorded from a driver’s angle. The survey results showed that a vast majority (69.5%) of survey participants selected the combination of placing “WRONG WAY” signs on both the left and right sides of an interstate off-ramp with red RRFBs activated at the top and bottom as the method that most gets their attention and informs them of wrong-way driving. Additionally, approximately 58% of participants selected the non-dimmed flashing red RRFBs over the dimmed option. This study offers important findings essential for the future determination of using red RRFBs as an optional supplement to the existing standards in MUTCD to reduce wrong-way driving.

Updated Commercial Truck Speed Versus Distance–Grade Curves for the Highway Capacity Manual

The current version of the Highway Capacity Manual 2010 (HCM 2010) gives guidance on commercial truck speeds on grade through the use of truck speed versus distance–grade curves, which are located in the HCM 2010, Chapter 11. These curves are designed to allow the analyst to estimate a commercial trucks speed after it travels on a known distance of roadway with a certain grade. Typically, these curves are used to determine an equivalent grade (incline–decline and length) that will result in the same final speed of commercial trucks as would the series of grades making up a composite grade. The HCM 2010 curves were developed as a result of studies that used simulation tools. These simulation tools used a simple lookup table approach for maximum acceleration versus speed and did not account for commercial truck transmission gear–changing capabilities. These shortcomings, along with changes in truck performance over the past 20 years, necessitate an update to the HCM 2010 speed versus distance–grade curves. This study presents the development of updated speed versus distance–grade curves for commercial trucks by using TRUCKSIM. This simulation tool uses a modeling approach of full-vehicle dynamics, which ensures that commercial truck performance is accurately represented for field conditions. The results show that the performance of commercial trucks, as presented in the HCM 2010, is worse than that currently observed. Therefore, the authors recommend that the current speed versus distance–grade curves included in the HCM be replaced with those presented in this study.