2016.04.04 CC Packet - Laserfiche WebLink

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of 1,000. The tube locations will include between 24 and 48 hours of data, including the following data elements for each vehicle: time stamp, travel speed, and vehicle classification. For the locations with greater than 1,000 ADT, manual speed samples will be collected with a radar unit. A minimum of 100 vehicles will be measured and classified as either a passenger vehicle or commercial truck. Field Investigations Field investigations are needed to assess the general environment of the roadway. These elements were chosen not because they necessarily have a direct or indirect impact on travel speed, but rather to provide a general snapshot of the environment of the study segment to the Mn DOT District Traffic Engineer. Along with speed sample data and crash analysis, results of the field investigation will be considered in determining whether a roadway can safely support a 60 mph speed limit. Measurements are taken at a point location that is considered to be representative of the entire section. • Travel Lanes and Shoulders. Travel lane and shoulder width, combined with pavement/gravel condition will be assessed. Travel lanes of at least 11 feet and usable shoulders of at least 5 feet are preferred. • Rumble Strips. Shoulder and/or centerline rumble strips are preferred for those locations that potentially could receive increased speed limits. • Access Density. Public street intersections, private driveways, and field entrances are counted and the total will be divided by the length of the corridor. Numerous studies have shown that crash rates rise as access density increases. Average access density of no more than 10 accesses per mile is desired. • Vertical Grades. It is preferred that corridors do not contain large numbers of vertical grades in excess of 3%. • Roadside Assessment. Roadside environments with large concentrations of fixed objects or other hazards would not be conducive to increased speed limits. • Inslope. Inslopes of 1v:4h or Flatter are desired. • Adjacent Development. No specific thresholds are set relative to adjacent development. This is a subjective data element intended to inform the district traffic engineer of the general environment of the corridor, such as rural residential, agricultural, plains, or forest. • Speed Reductions. All regulatory and advisory speeds will be noted. Reductions in regulatory speed limits typically occur in areas near or in cities, or if the road environment otherwise changes significantly so that it no longer can safely support a 55 mph speed limit. Advisory speed reductions typically are associated with curve warning signs, but could be included as a supplemental plaque on any warning sign. • Intersection Control. All traffic signals, roundabouts, and intersections with mainline stop control will be noted along the study segment, including those at the beginning and ending termini. Analysis and Reporting Stonebrooke's role is to perform speed studies and field investigations, analyze speed an crash data, and provide reports to Mn DOT. The ultimate authority to determine whether 60 mph speed limits are appropriate remains with Mn DOT. Analysis of crash data includes calculating overall crash rates and Fatal + "A" severity crash rates for the study segment and comparing to average and critical crash rates. A critical crash rate is a statistically adjusted crash rate to account for random nature of crashes. If segment's crash rate exceeds the critical rate, it is not a good candidate for an increased speed limits without other structural improvements. Speed data from both tubes and radar will be analyzed. The primary calculations will include 85th percentile and 10 mph pace. "Good" speed samples are considered to be those that have the 85th percentile in the upper range of the 10 mph pace. The 85th percentile is the speed that is not exceeded by 85% of the population. This value is generally considered a good starting point for setting speed limits. The 10 mph pace is the 10 mph range of speeds that include the highest percentage of vehicles from the sample. When all the data collection, field investigations, and analysis is complete, Stonebrooke staff will assemble a report for each study segment. The reports are organized such that the front page provides an at -a - glance look at crash rates, speed sample results, and field investigation findings. Field investigation findings are reported with either green shading or no shading at all. Green shading indicates that the particularly data element measured in the field likely would be conducive to an increased speed limit. No shading indicates that a deeper look into that particular data element may be warranted. The first page will provide the Mn DOT district traffic engineer with a good indication of whether this comidor is a good candidate for a 60 mph speed limit - a high 85th percentile speed coupled with a low crash rate and lots of green shading would like be a good candidate. The second page provides a more detailed description of the study, and subsequent pages provide pictures and other additional information. If desired, MnDOT