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HomeMy WebLinkAboutemail Banihatti on conversion standardsMalone, Walter From: Banihatti, Nat Sent: Thursday, March 20, 2014 9:22 AM To: Malone, Walter Cc: Henry, Bill; Herbner, Travis Subject: 4 -lane to 3 -lane coversion; Traffic Volume Guidelines Attachments: 4 -lane to 3 -lane conversion.pdf Walter: Attached is the information. I have marked the relevant paragraphs. I didn't send you the entire report as it is 120 pages. Basically, the conversion works well for volumes up to 15,000 vpd, when you don't have signalized intersections in the concerned segment. If you have traffic signals, it is a different scenario. -Nat. GUIDELINES FOR THE CONVERSION OF URBAN FOUR-L.ANE UNDIVIDED ROADWAYS TO THREE-LANETwo-WAY LEFT -TURN LANE FACILITIES FINAL REPORT Sponsored by the Office of Traffic and Safety of the Iowa Department of Transportation CTRE Management Project 99-54 APRIL 2001 Center for rransportation Research and Education IONVA STATE UNIVERSITY 0Iowa Department 4 of Tra nsporta tion CONCLUSIONS AND RECOMMENDATIONS Conclusions The following conclusions are based on the findings past research, and the results of case study and simulation analysis investigations completed as part of this project. Most cross section improvement research has focused on the advantages and disadvantages of the addition of a raised median or TWLTL to a currently undivided roadway. The addition of a TWLTL or raised median to an undivided roadway typically reduces through - vehicle delay. ® The addition of a TWLTL or raised median to an undivided roadway typically reduces crash rates. —.--In-certain-ciretimstaiices,the-.conv-ersion-of a four=lane-undi-videdroadway-to-axhree-lane-cross-- section can be a feasible improvement alternative, but not necessarily the preferable alternative, at a particular location. ■ Typically, a reduction of less than five mph has been observed and/or simulated in average arterial or 85th percentile speed after a four -lane undivided to three -lane cross section conversion. The magnitude of the change depends upon the current operation of the four -lane undivided roadway and a number of other factors (e.g., total volume, turn volume, access density, and signal timing changes). ■ Measurements in the field show that several case study conversions resulted in a reduction of the number of drivers traveling five mph or more above the posted speed limit. These reductions can be significant (e.g., for two case studies it was measured between 60 to 70 percent). This reduction in speeders is a measure of the "traffic calming" effect produced by a four -lane undivided to three -lane cross section conversion. Some four -lane undivided roadways currently operate as "defacto" three -lane roadways (especially during the peak period). The total number of crashes is typically reduced (from 17 to 62 percent for the case studies identified) when a four -lane undivided roadway is converted to a three -lane cross section. • Four -lane undivided roadways with an ADT between 8,400 and 24,000 vpd, and a relatively wide range of traffic flow and physical characteristics, have been successfully converted to three -lane cross sections in many areas of the United States and Iowa. The results of the simulation sensitivity analysis completed as part of this project support the conclusion four -lane undivided to three -lane cross section conversions, when done properly and in the correct location, can have minimal operational disadvantages. s The simulation sensitivity analysis completed as part of this project helped identify the average arterial travel speed and LOS impacts (i.e., operational feasibility) of a four -lane undivided to ee-ane conversion along a roadway Wifftc i rent totaTentering volumes, left -tum volumes, and access densities. ■ The three -lane cross section can easily be incorporated as a potentially feasible alternative in to the cross section selection guidelines suggested in past research. • The life -cycle costs and benefits, increased delay and decreased crashes, of a four -lane undivided to three -lane cross section conversion should be compared to the impacts from typical widening alternatives to determine the preferable improvement. Recommendations The following actions are recommended based on the results of this project report and the discussions in these guidelines. The feasibility of replacing an urban four -lane undivided roadway with a three -lane cross section should be considered on a case-by-case basis. 67 At a minimum, the existing and expected characteristics of the following feasibility determination factors should be investigated when considering the design period feasibility of a four -lane undivided to three -lane cross section conversion: Roadway Function and Environment Overall Traffic Volume and Level of Service Turn Volumes and Patterns D Frequent -Stop and/or Slow -Moving Vehicles Weaving, Speed, and Queues Y Crash Types and Patterns D Pedestrian and Bike Activity Y Right -of -Way Availability, Cost, and Acquisition Impacts y General Characteristics: Parallel Roadways, Offset Minor Street Intersections, Parallel Parking, Corner Radii, and At -Grade Railroad Crossings .- _The..content of these.guideFina- along -with the.sununa.ry..tables.in.the..executive-sununary.and___---.-- . Appendix C should be used to assist with the investigation of the factors discussed and to determine the feasibility of a four -lane undivided to three -lane cross section conversion. From an operational point of view, it is suggested that four -lane undivided to three -lane cross section conversions be considered as a feasible (with respect to volume only) option when bi- directional peak -hour volumes up are less than 1,500 vph, but that more caution should be exercised when the roadway has a bi-directional peak hour volume between 1,500 vph and 1,750 vph. At and above 1,750 vph, the simulation indicated a reduction in arterial level of service. Therefore, at least in Iowa, the feasibility of a four -lane undivided to three -lane cross section conversions should be questioned and/or considered much more closely when a roadway has (or is expected to have) a peak hour volume above 1,750 vph. Assuming that these volumes represent 10 percent of the ADT along corridor, they are equivalent to 15,000 vpd and 17,500 vpd. These recommendations are based on the simulation analysis of an idealized case study corridor, and the expected operational impacts should be considered and 68