Four-Lane to Three-Lane Conversions In Iowa: A Summary Results from Several Research Studies of the Impacts on Safety Iowa Department of Transportation Office of Traffic and Safety Iowa State University Center for Transportation Research and Education

Preface The research results I am presenting belong to others. Their permission in doing so is greatly appreciated.

The Researchers Michael Pawlovich, Iowa DOT Alicia Carriquiry, ISU Statistics Department Win Lee, ISU Statistics Department Tom Stout, CTRE Keith Knapp, formerly CTRE Karen Giese, formerly CTRE Tom Welch, Iowa DOT (sponsor)

Presentation Outline 4 lane to 3 lane basics Results from “traditional” safety studies Results from Bayesian safety study Conclusions

The Basics Converting an existing 4- lane roadway to a 3- Converting an existing 4- lane roadway to a 3- lane roadway  typically 2-lanes with a center lane roadway  typically 2-lanes with a center continuous two-way left- turn lane (TWLTL) continuous two-way left- turn lane (TWLTL) The addition of the turn lane is the critical ingredient for improved traffic flow and safety The addition of the turn lane is the critical ingredient for improved traffic flow and safety May free up enough room for bike lanes or parkingMay free up enough room for bike lanes or parking Source: Huang et al./HSIS 2002,2004,2005

The Iowa 4 Lane To 3 Lane Experience Iowa DOT sees these conversions as positive in terms of both safety and quality of life Before After

Conversion Guidelines When conversions seem to make sense ADT < 20,000 ADT < 20,000 Urban or small city arterial or collector with a posted speed of 30 to 45 mph Urban or small city arterial or collector with a posted speed of 30 to 45 mph History of left-turn related crashes History of left-turn related crashes Broadside and rear end collisions Significant commercial and/or residential driveway density Significant commercial and/or residential driveway density Question: is there a density that is too high? Significant left-turning volumes Significant left-turning volumes

Two Example 4-Lanes Source: Iowa DOT RoadView Storm Lake, IA – US 7 EB  !!! Left-turning vehicle slows van Clear Lake, IA – US 18 EB (west of Clear Lake)

Two Example 3-Lanes Source: Iowa DOT RoadView Storm Lake, IA – US 7 EB Left-turning vehicle has no effect

Drive Through: Sioux Center, IA US 75 NB

Source: Iowa DOT RoadView 1/8 Long transition length Multiple signs

2/8 Source: Iowa DOT RoadView From 45 mph

3/8 Source: Iowa DOT RoadView Passed after signage

4/8 Source: Iowa DOT RoadView Plenty of time to change lanes

5/8 Source: Iowa DOT RoadView Left-turning van Opposing flow queue headways 4-lane to 3-lane transition

6/8 Source: Iowa DOT RoadView Parallel Parking Multiple left-turning pickups Opposing flow queue headways

7/8 Source: Iowa DOT RoadView Signing and traffic markings

8/8 Source: Iowa DOT RoadView 3-lane to 4-lane transition

Drive Through: Sioux Center, IA US 75 SB

1/8 Source: Iowa DOT RoadView Long transition length Multiple signs From 45 mph to 35 mph

2/8 Source: Iowa DOT RoadView Multiple signs

3/8 Source: Iowa DOT RoadView 3-lane section begins

4/8 Source: Iowa DOT RoadView Parallel Parking Multiple left-turning vans, pickup to turn right-on-red soon

5/8 Source: Iowa DOT RoadView Parallel Parking Van finishes left movement, pickup turns right-on-red

6/8 Source: Iowa DOT RoadView Parallel Parking Right-turning car, van waiting for opposing left, opposing thru traffic not hindered $1.52/gallon!!!

7/8 Source: Iowa DOT RoadView More lefts and thru traffic Pedestrian signs Parallel Parking

8/8 Source: Iowa DOT RoadView 3-lane to 4-lane transition

Analysis History  Treatments in Iowa (All Potential Case Studies)  15 from 1993 – 2003  2001: Guidelines (CTRE)  4 to 3 Conversion Safety Impact Studies  2002: Huang et al. (FHWA/HSIS) Showed small reduction in crash density and no reduction in crash rate (this study is the “odd duck” here)  Fall 2004: Matched-Pair Before/After (CTRE)  Spring 2005: Bayesian Before/After (ISU Statistics Department)

Yoked Pair Comparison 4-3 conversion segments were compared with similar “control” segments City population within 20% Corridor traffic (AADT) within 20% Physically similar (length, land use, access management, etc.)

Yoked Pair Results Net effect – 27 to 28% reduction in crash rate

Crash Rate Analysis Before – 8.86 per MVM After – 4.45 per MVM

Older Driver Analysis How did older drivers fare? Age 65 and older – average crash rate of 7 before (on the 4 lane), 2.9 after (on the 3 lane) Age 75 and older – average of 3.3 before, 1.5 after

Younger Driver Analysis How about younger drivers? Age 25 and younger – average of 28.1 before, 13.3 after If you have teenagers, now you know why their insurance rates are so high!

Injury Crashes Only Net benefit, 27% reduction in injury crashes

Conclusions Overall crash frequency reduction of 21% Improved crash rate (27-28% reduction) Improvements for both older and younger drivers Reduced injury numbers and rate

Bayesian Before/After Study  Objective: Assess whether 4 lane to 3 lane conversions appear to result in crash reductions on Iowa roads  Control for “regression to the mean” phenomenon  Sometimes, crash rate improvements are simply random  Much more rigorous study than the “traditional” study just described

Bayesian Before/After  Data  15 treatment and 15* control  23 years ( )  Volumes: 2,030 to 15,350 ( ) * One control site served as a matched pair for two treatment sites.

Data  3-lane (treatment sites) SIDCITYLITERAL CIPOP ADT Storm LakeIowa 7 from Lake Ave. to Lakeshore Dr.10,0767,503 2Clear LakeUS 18 from N 16 St. W to N 8th St.8,16110,403 3Mason CityIowa 122 from West intersection of Birch Drive to a Driveway29,1727,800 4OsceolaUS 34 from Corporate limits on east side to where highway divides to 4 lanes on west side4,6598,172 5ManchesterIowa 13 from River St. to Butler St.5,2579,400 6Iowa FallsUS 65 from City Limits - ? to Park Ave.5,19310,609 7Rock RapidsIowa 9 from S Greene St. to Tama St.2,5734,766 8GlenwoodUS 275 from MP 36.2 to MP ,3586,410 9Des MoinesBeaver Ave from Urbandale Ave. to Aurora Ave.198,68213,695 10Council BluffsUS 6 from McKenzie Ave. west 1300 ft.58,26811,000 11Blue GrassOld US 61 from Oak Lane to 400' W of Terrace Drive1,1699,155 12Sioux CenterUS 75 from 200' South of 10th St. S. to 250' North of 9th St. NW6,0028,942 13IndianolaIowa 92 from South R St. to Jct. of US 65/6912,99813,288 14LawtonUS 20 from 100' east of Co. Rd. Eastland Ave. to 1130' West of Co. Rd. Emmet Ave.6979,237 15Sioux CityTransit Ave. from Vine Ave. to just west of Paxton St. at curve85,0139,608

Data  4-lane (control sites) SIDCITYLITERAL CIPOP ADT Storm LakeIowa 7 from Lake Ave. to Barton St10,0768,790 19Le MarsUS 75 from 0.01 miles north of 3rd St NW to 0.36 miles SW of 12th St SW9,23710,880 20Cedar FallsGreen Hill Road from 0.10 miles east of IA 58 to 0.09 miles west of Cedar Heights Dr.36,1452,768 21JeffersonIowa 4 from National Ave to 0.13 miles north of 250th Ave4,6265,685 22HarlanIowa 44 from US 59 to 6th St5,2826,981 23NorwalkIowa 28 from 0.03 miles south of Gordon Ave to 0.04 miles south of North Ave6,8847,679 24BelmondUS 69 from 0.38 miles north of Main St to 0.58 miles south of Main St2,5603,734 25HarlanIowa 44 from US 59 to 6th St5,2826,981 26Des MoinesHickman Road - 40th Place east to 0.07 miles west of W 18th St198,68213,953 27Ames13th Street from 0.09 miles east of Stange Road to 0.07 miles west of Crescent Circle Dr.50,73110,711 28MapletonIowa 141 from 0.02 miles north of Sioux St. to 0.08 miles south of Oak St.1,3223,007 29AlgonaUS 169 from 0.07 miles south of US 18 to 0.23 miles south of Irvington Rd.5,7417,263 30OskaloosaIowa 92 from 0.12 miles east of IA 432 to 0.07 miles west of Hillcrest Dr10,93811,143 31MerrillUS 75 from 0.05 miles north of 2nd St to 0.18 miles north of Jackson St7547,774 32Sioux CityS. Lakeport from 4th Ave to Lincoln Way85,01315,333

Data  Pairings* SIDROUTELENGTH 1IA US IA US IA US IA US Local US Local US IA US Local0.77 COMPYEAR TreatmentControl SIDROUTELENGTH 18IA US Local IA IA IA US IA Local Local IA US IA US Local1.20 * Not essential for Bayesian, more for discussion purposes

Monthly Crash Densities Treatment Control

Monthly Crash Rates Intervention

Modelling/Statistics  Crashes: random, rare count events  Model: Poisson w/ log mean expressed as a piece- wise linear function of: wise linear function of: - time period (months) - time period (months) - seasonal effects - seasonal effects - random effect for each site - random effect for each site  Adopted a Bayesian statistical framework for estimation of model parameters estimation of model parameters

Results/Discussion  25.2% (23.2% %) in crashes/mile 25%  18.8% (17.9% %) in crash rate 19%

Results/Discussion  Agrees with:  CTRE Matched-pair Before/After study  Why? Prior Sioux Center speed study  4-5 mph in 85th percentile free flow speed speed  12-14% in percentage of vehicles traveling more than 5 mph over the speed limit traveling more than 5 mph over the speed limit (i.e., vehicles traveling 35 mph or higher). (i.e., vehicles traveling 35 mph or higher).

Conclusions 4 lane to 3 lane conversions appear to be successful treatments for calming traffic under the right conditions They can be very effective in improving traffic safety They are not especially problematic for either elderly or young drivers