10-02-2017 Council Packet - Laserfiche WebLink

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The Level 1 speed study will consist of speed data collected by a speed trailer or tube counters. In analyzing the speed data, the Pace of the traffic and the 85th Percentile Speed will be calculated from this data. Pace and 85th Percentile speed are defined as follows: • Pace – The 10 MPH range of speeds containing the largest number of observations • 85th Percentile Speed – The speed at or below which 85 percent of the traffic is moving. Typically, the 85th Percentile Speed is within two miles per hour of the upper limit of the Pace. A normal speed distribution will contain approximately 70% of the sample within the Pace with 15% above and 15% below. Based on the data collected, a preliminary speeding issue will be identified if: • The calculated 85th Percentile speed from the Level 1 data is greater than the posted speed. • More than 15% of the vehicles are traveling faster than the 10 MPH Pace. NOTE: Federal and State speed limit guidelines define the 85th percentile speed as a “reasonable speed” or the speed in which 85% of motorists travel at or below. Experience has shown that the 85th Percentile Speed most closely provides for a safe and reasonable speed limit. Therefore, it can be expected that on a typical roadway, approximately 15 percent of the vehicles may traveling at speeds greater than the posted speed limit. If a preliminary speeding issue is identified, City staff will first determine if low cost measures are feasible. If low cost measures are not feasible, the process will skip to the next step. Some low cost measures include: • Education and enforcement • Lane narrowing (striping) • Pavement messages (30 MPH, SLOW) • Additional signage • Improve sight lines through tree / branch removal or grading (safety improvement) If low cost measures are deemed feasible, the appropriate measures will be implemented by the City once funding is secured. Possible funding sources include: • Inclusion in the City’s Capital Improvement Plan (CIP) • Special request from the City Council The City will then monitor the traffic conditions over a 3-month period. After the 3-month period, the City will then collect new speed data. If the analysis indicates a speeding problem still exists, education and enforcement will continue while a Level 2 analysis is conducted. Level 2 Analysis: A Level 2 analysis consists of a formal speed study to determine the actual, free flow speed of vehicles on a roadway. A formal speed study differs from tube counts or speed trailer collected data in that recorded speeds reflect how vehicles typically travel along unimpeded sections of the road under free flow conditions. Therefore, not all vehicles have their speeds recorded as with tube counters or speed trailers. Only the lead vehicle in a platoon of vehicles has its speed recorded. This is because the trailing vehicles’ speeds are being metered by the lead vehicle and don’t necessarily reflect free flow conditions.