Converting a couple of Clinton streets from four lane to three lane with the middle lane being a left turn lane will be the topic of a couple of public meetings this week.
City Engineer Jason Craft has proposed the change for the Second Avenue South from South 14th Street to Bluff Boulevard and for Springdale Drive from 13th Avenue North to North Bluff. Click ‘read more for details.
There will be a public meeting on Wednesday, March 4, 2015, from 5:30 p.m. to 6:30 p.m. at the Ericksen Center, located at 1401 11th Avenue North, concerning the proposal to change 2nd Avenue South (from South 14th Street to South Bluff Blvd.) to a three lane roadway. The feasibility of converting 2nd Avenue South to a three lane road is being considered due to the potential safety and operational benefits.
There will be a public meeting on Wednesday, March 4, 2015, from 6:30 p.m. to 7:30 p.m. at the Ericksen Center, located at 1401 11th Avenue North, concerning the proposal to change Springdale Drive (from 13th Avenue North to North Bluff Blvd.) to a three lane roadway. The feasibility of converting Springdale Drive to a three lane road is being considered due to the potential safety and operational benefits.
The conversion of four lane roadways to three lane roadways has occurred throughout the State of Iowa in many cases over the past several years. In certain situations, the conversion of a four lane undivided roadway to a three lane cross section has been proven to produce acceptable operational and improved safety results.
The Center for Transportation Research and Education (CTRE), Iowa State University, conducted a study in 2006, which indicated a 21 percent reduction in total crash frequency and a 29 percent reduction in total crash rates on roadways where the conversion has occurred.
The Federal Highway Administration report of four lane to three lane conversions at 15 different sites across the state of Iowa shows drastic crash reduction statistics in the years after the conversions. The data from that study shows an average of 23.74 crashes per mile in the years before the conversion, and 12.19 crashes per mile in the years after the conversion, or an approximate 47 percent total crash reduction.
There are five major reasons that accidents are commonly reduced by four lane to three lane conversions, and they are:
1. Without the ability to pass in the inside or outside through lane (because only 1 through lane exists), traffic will drive at a speed consistent with the normal flow of traffic. This will lower average speeds by at least 5 mph, which will decrease accidents.
2. The three lane conversion involves two 12-foot outer lanes and a 14-foot center turn lane. This allows a 1 foot offset from the curb line. This alone will decrease accidents, as traffic will have more room for error as the lane widens.
3. The inclusion of dedicated left turn lanes throughout the corridor will allow for safe queuing of left turning vehicles. Also, the left turning vehicles will only have to judge one lane of opposing oncoming traffic, which will lead to fewer poor decisions and decreased traffic accidents.
4. Through traffic will no longer be adversely impacted by turning vehicles using the same lane. All through traffic will be allowed to free flow in the outside lanes. This will result in decreased delays throughout this corridor, and fewer accidents due to impatient road decisions.
5. Traffic approaching 2nd Avenue South from intersections or private driveways will more easily be able to judge oncoming traffic while turning out onto 2nd Avenue South, as the number of through lanes are reduced from four to two.
As described in the five points above, traffic accidents will decrease due to the conversion from four lanes to three lanes on 2nd Avenue South, from South 14th Street to South Bluff Blvd.
A common misconception is that highway capacity will be decreased during a conversion from a four lane road to a three lane road. In fact, with traffic thresholds under 17,000 vehicles per day, only one through lane in each direction is needed. Actual capacity is derived from the inclusion of the dedicated left turn lane. In roadways with a high volume of turning traffic (due to many access points and narrow lanes), the conversion of a roadway from 4 lanes to 3 lanes is a tried and true method to increase functionality, capacity, and safety of the roadway.
The City Engineering Department recommends the conversion of 2nd Avenue South, from South 14th Street to South Bluff Blvd, to a three lane road with a center two way left turn lane. A comprehensive feasibility study on the proposed three lane conversion of 2nd Avenue South is available at the City Engineering Department. There are not expected to be any adverse consequences due to the conversion. As discussed in the study, the conversion should occur as part of the 2015 resurfacing project.
As described in the five points above, traffic accidents will decrease due to the conversion from four lanes to three lanes on Springdale Drive, from 13th Avenue North to North Bluff Blvd.
A common misconception is that highway capacity will be decreased during a conversion from a four lane road to a three lane road. In fact, with traffic thresholds under 17,000 vehicles per day, only one through lane in each direction is needed. Actual capacity is derived from the inclusion of the dedicated left turn lane. In roadways with a high volume of turning traffic (due to many access points and narrow lanes), the conversion of a roadway from 4 lanes to 3 lanes is a tried and true method to increase functionality, capacity, and safety of the roadway.
The City Engineering Department recommends the conversion of Springdale Drive, from 13th Avenue North to North Bluff Blvd, to a three lane road with a center two way left turn lane. A comprehensive feasibility study on the proposed three lane conversion of 13th Avenue North is available at the City Engineering Department. There are not expected to be any adverse consequences due to the conversion. As discussed in the attached study, the conversion should occur as part of the 2015 resurfacing project.
