# Presentation: 139884

## Iowa’s Experience with	Two-lane to Three-lane Conversions

**Wen Li, Master’s Student**
**and**
**Dr. Alicia Carriquiry**
**Iowa State University Department of Statistics,**
**Dr. Michael Pawlovich, PE**
**and**
**Tom Welch, PE**
**Iowa DOT Office of Traffic and Safety**

**for**
**the Iowa Department of Transportation**
**Office of Traffic and Safety**

## Preliminary Results

-  Density:  12 percent   (reduction)
-  Rate:  34 percent     (reduction)

- NO control sites – so preliminary results – future effort

**Notes:**
The arrow points down meaning 12 percent reduction in density and 34 percent reduction in rate

## What

-  Converting an existing 2-lane roadway to a 3-
-      lane roadway  typically 2-lanes with center
-      continuous left-turn lane
-   Important  left-turn lane
-  Also – sometimes bike lanes and pedestrian 	accommodations

## What:  3-lane

**What:  3-lane**

- Source:  Iowa DOT RoadView

- Arnold’s Park, IA – US 71 NB

**Notes:**
Picture: Arnold’s Park, IA-US 71 NB. The photo shows a 3-lane section of Arnold’s Park road in Iowa intersecting with US 71 NB

## What:  3-lane

**What:  3-lane**

- Source:  Iowa DOT RoadView

- Arnold’s Park, IA – US 71 NB

**Notes:**
Picture: Arnold’s Park, IA-US 71 NB. The photo shows another 3-lane section of Arnold’s Park road in Iowa

## What:  3-lane

**What:  3-lane**

- Source:  Iowa DOT RoadView

- Arnold’s Park, IA – US 71 NB

**Notes:**
Picture: Arnold’s Park, IA-US 71 NB. The photo shows another 3-lane section of Arnold’s Park road in Iowa

## What:  3-lane

**What:  3-lane**

- Source:  Iowa DOT RoadView

- Indianola, IA – IA 92 NB

**Notes:**
Picture: Indianola, IA-US 92 NB. The photo shows a 3-lane section of Indianola road in Iowa intersecting with IA 92 NB

## What:  3-lane

- Source:  Iowa DOT RoadView

- Harlan, IA – US 59 NB

**Speed limit**

- Note: Oncoming van is entering turn lane with vehicle behind it.  Speed limit is 45 mph thru the school site.

**Harlan, IA**

**School**

**Notes:**
Picture: Harlan, IA-US 59 NB. The photo shows a 3-lane section of Harlan road in Iowa intersecting with US 59 NB
Picture: School. The photo shows the school within the vicinity of the intersection of Harlan road with US 59 NB in Iowa 
Picture: Speed limit. The photo shows two (2) speed signs ( 45 mph and 55 mph). There are flashers on the 45 mph sign to indicate reduced speed in the school zone when flashing

## History

-  Treatments in Iowa
-  35 from 1981 – 2004
-  28 from 1991 – 2004
-  Studies
-  2005 – Florida DOT

## Bayesian Before/After

-  Objective:  Assess whether 2-lane to 3-lane
-                      conversions appear to result in crash
-                      reductions on Iowa roads

## Bayesian Before/After

-  Data
-  34 treatment – 1 dropped as treatment in 1981
-  25 years (1982-2006)
-  Volumes: 2,500 to 15,700 (1982-2006)
-  Currently NO control sites – future effort

## Site Data

| Site ID | City | Population 2000 | Volume 2000 |
| --- | --- | --- | --- |
| 1 | Ames | 50,731 | 6,800 |
| 2 | Ames | 50,731 | 7,900 |
| 3 | Ames | 50,731 | 7,500 |
| 4 | Ames | 50,731 | 8,500 |
| 5 | Ames | 50,731 | 5,000 |
| 6 | Ames | 50,731 | 12,200 |
| 7 | Ames | 50,731 | 10,000 |
| 8 | Arnolds Park | 1,162 | 15,700 |
| 9 | Atlantic | 7,257 | 8,000 |
| 10 | Council Bluffs | 58,268 | 8,200 |
| 11 | Creston | 7,597 | 5,300 |
| 12 | Davenport | 98,359 | 9,500 |
| 13 | Davenport | 98,359 | 8,500 |
| 14 | Dyersville | 4,035 | 9,000 |
| 15 | Eldridge | 4,159 | 7,100 |
| 16 | Harlan | 5,282 | 5,300 |
| 17 | Hull | 1,960 | 4,400 |
| 18 | Indianola | 12,998 | 13,500 |

| Site ID | City | Population 2000 | Volume 2000 |
| --- | --- | --- | --- |
| 19 | Iowa City | 62,220 | 10,000 |
| 20 | Iowa City | 62,220 | 7,500 |
| 21 | Manchester | 5,257 | 7,900 |
| 22 | Manchester | 5,257 | 7,500 |
| 23 | Maquoketa | 6,112 | 10,000 |
| 24 | Mason City | 29,172 | 3,200 |
| 25 | Mason City | 29,172 | 7,400 |
| 26 | Nevada | 6,658 | 3,400 |
| 27 | Nevada | 6,658 | 5,600 |
| 28 | Nevada | 6,658 | 4,000 |
| 29 | New London | 1,937 | 2,500 |
| 30 | Newton | 15,579 | 11,500 |
| 31 | North Liberty | 5,367 | 11,500 |
| 32 | Oelwein | 6,692 | 5,000 |
| 33 | Orange City | 5,582 | 4,500 |
| 34 | Pella | 9,832 | 3,200 |
| 35 | Waverly | 8,968 | 6,000 |

**Note:  Maquoketa dropped from analysis (1981)**

**Notes:**
The red highlighted cell means site ID 23, Maquoketa city with a population of 6112 and traffic volume of 10000 vehicles per day in the year 2000 was dropped from the analysis

## Site Data

| Site ID | City | Length (mi) | Completion Year |
| --- | --- | --- | --- |
| 1 | Ames | 0.50 | 2003 |
| 2 | Ames | 0.80 | 2002 |
| 3 | Ames | 0.35 | 1998 |
| 4 | Ames | 0.45 | 1996 |
| 5 | Ames | 0.25 | 2004 |
| 6 | Ames | 0.30 | 1998 |
| 7 | Ames | 0.50 | 2001 |
| 8 | Arnolds Park | 1.80 | 2000 |
| 9 | Atlantic | 2.00 | 1994 |
| 10 | Council Bluffs | 0.85 | 1995 |
| 11 | Creston | 0.32 | 2004 |
| 12 | Davenport | 1.00 | 1992 |
| 13 | Davenport | 0.90 | 2003 |
| 14 | Dyersville | 0.50 | 1987 |
| 15 | Eldridge | 0.60 | 2001 |
| 16 | Harlan | 2.17 | 2001 |
| 17 | Hull | 0.25 | 1997 |
| 18 | Indianola | 1.60 | 1983 |

| Site ID | City | Length (mi) | Completion Year |
| --- | --- | --- | --- |
| 19 | Iowa City | 0.45 | 1997 |
| 20 | Iowa City | 0.75 | 2001 |
| 21 | Manchester | 0.20 | 2000 |
| 22 | Manchester | 0.50 | 2000 |
| 23 | Maquoketa | 0.80 | 1981 |
| 24 | Mason City | 1.00 | 2003 |
| 25 | Mason City | 1.00 | 1998 |
| 26 | Nevada | 0.25 | 2002 |
| 27 | Nevada | 0.25 | 2002 |
| 28 | Nevada | 1.00 | 1999 |
| 29 | New London | 0.25 | 1985 |
| 30 | Newton | 0.90 | 1982 |
| 31 | North Liberty | 0.50 | 2000 |
| 32 | Oelwein | 1.00 | 1984 |
| 33 | Orange City | 1.00 | 1991 |
| 34 | Pella | 1.20 | 1985 |
| 35 | Waverly | 1.85 | 1997 |

**Note:  Maquoketa dropped from analysis (1981)**

**Notes:**
The red highlighted cell means site ID 23, Maquoketa city with a population of 6112 and traffic volume of 10000 vehicles per day in the year 2000 was dropped from the analysis

## Monthly Crash Densities and Rates

**Monthly Crash Densities and Rates**

- Site 4

**Intervention**

- Density

- Rate

**Notes:**
Graph. Site 4. Site 4 has two(2) graphs: The graph above shows monthly crash densities. The dots indicate the raw data and the smooth line indicate the smoothed data. The x-axis is the month axis ranging from 0 to 300. The y-axis is the density axis ranging from 0 to 10. The red vertical line between months 150 and 200 shows the period of intervention. The smooth line a slight decrease in crash density over time
The graph below shows monthly crash rates. The dots indicate the raw data and the smooth line indicate the smoothed data. The red vertical line between months 150 and 200 show the period of intervention. The x-axis is the month axis ranging from 0 to 300. The y-axis is the density axis ranging from 0 to 50. The red vertical line between months 150 and 200 shows the period of intervention. The smooth line a slight decrease in crash density over time

## Modeling/Statistics

-  Crashes:  random, rare count events
-  Model:  Poisson with/ log mean expressed as a piece-wise linear function of:
-                     - time period (months)
-                     - seasonal effects
-                     - random effect for each site
-  Adopted a Bayesian statistical framework for
-      estimation of model parameters
-  Model essentially the same as for prior 4-lane to 3-
- 	  lane analysis

## Preliminary Results/Discussion

-  12%   (reduction) in crashes/mile
-  34%    (reduction) in crash rate
-  Recall NO control sites – so preliminary results

## Results/Discussion

-  Prior Florida DOT study:
-  32 percent decline in crashes
-  not “significant” at 95 percent confidence level
-  Need to include control sites - future

## Questions?&Discussion