(a) Regression models developed for safety edge treatment (Model 1)

Model variables

All crash type

Lane-departure crashes

Fatal and injury

All crashes

Fatal and injury

All crashes

Parameter Estimates

Standard Error

(p-value)

Parameter Estimates

Standard Error

(p-value)

Parameter Estimates

Standard Error

(p-value)

Parameter Estimates

Standard Error

(p-value)

Intercept

−8.901

3.4037

(0.0089)

−8.176

4.3537

(0.0604)

18.216

30.5747

(0.5513)

−16.039

7.409

(0.0304)

Safety edge

−0.243

0.1521

(0.1103)

−0.261

0.2904

(0.3692)

−0.154

0.2934

(0.6004)

−0.277

0.3023

(0.3593)

Segment Length

0.333

0.0586

(<0.0001)

0.319

0.1062

(0.0026)

0.223

0.0949

(0.0186)

0.336

0.1045

(0.0013)

Posted speed limit

4.285

1.359

(0.0016)

0.007

0.0035

(0.0569)

0.521

2.1276

(0.8064)

5.286

3.4684

(0.1275)

AADT

2.031

0.4064

(<0.0001)

2.210

0.8797

(0.012)

0.270

0.6846

(0.6929)

2.052

0.8257

(0.013)

Average lane width

0.093

0.0982

(0.3418)

0.288

0.195

(0.14)

0.217

0.0914

(0.0178)

0.301

0.1704

(0.0774)

Dispersion

0.375

0.590

0.352

0.278

(b) Regression models developed for adding 2 ft paved shoulders with rumble strips (Model 2)

All crash type

Lane-departure crashes

All crashes

Fatal and injury

All crashes

Parameter

Parameter Estimates

Standard Error

(p-value)

Parameter Estimates

Standard Error

(p-value)

Parameter Estimates

Standard Error

(p-value)

Parameter Estimates

Standard Error

(p-value)

Intercept

0.251

0.3134

(0.4240)

−0.196

0.3980

(0.6232)

0.238

0.3207

(0.4573)

-3.337

2.2393

(0.1362)

Segment length

0.667

0.0712

(<0.0001)

0.529

0.0742

(<0.0001)

−0.002

0.0018

(0.3412)

0.008

0.0074

(0.3017)

AADT

0.158

0.0441

(0.0003)

0.183

0.0492

(0.0002)

−0.073

0.0497

(0.1399)

0.071

0.0682

(0.3011)

Asphalt Resurfacing

−0.920

0.1661

(<0.0001)

−0.947

0.2356

(<0.0001)

0.237

0.1526

(0.1209)

0.308

0.2049

(0.1334)

Only 2 ft shoulders

0.256

0.1199

(0.0326)

0.102

0.1413

(0.4709)

−0.320

0.1388

(0.0214)

−0.313

0.186

(0.0922)

2 ft shoulders with rumble strips

−0.294

0.1365

(0.0311)

−0.661

0.1951

(0.0007)

−0.267

0.1501

(0.0758)

−0.623

0.2435

(0.0105)

Dispersion

2.347

2.087

2.336

1.921