APPENDIX J: ENCROACHMENT RATES, FREQUENCIES AND ADJUSTMENT FACTORS FOR FOUR-LANE DIVIDED HIGHWAYS. (KEY DETERMINANTS INCLUDE: POSTED SPEED LIMIT, TERRAIN TYPE, AND DENSITY OF MAJOR ACCESS POINTS ON THE HIGHWAY SEGMENT. THERE ARE THREE TALBLES IN TOTAL.) ROADSIDE ENCROACHMENT RATE, FREQUENCY & ADJUSTMENT FACTORS TABLES ROADWAY TYPE: FOUR-LANE DIVIDED HIGHWAYS STATISTICAL MODELS: POISSON-GAMMA REGRESSION MODEL, ESTIMATED FROM THE COOPER DATA (181 ROAD SEGMENTS) NOTES: (1) UNDERREPORTED ENCRO. ON SHOULDERS ARE ADJUSTED IN THE MODEL BASED ON ENCRO. DISTANCE MODELS DEVELOPED FROM THE SAME COOPER DATA. (2) INTENTIONAL/CONTROLLED ENCRO. ARE ASSUMED TO BE "ZERO" SINCE COOPER DATA TARGETED ONLY ENCRO. BEYOND SHOULDER AREAS AND VERY FEW OF THESE KINDS OF ENCRO. WOULD GO BEYOND SHOULDERS. THIS ASSUMPTION IS ALSO SUPPORTED BY COOPER~S ORIGINAL STUDY (CHAP. 2, 1981). (3) SAMPLE SIZE WAS TOO SMALL TO ESTIMATE TERRAIN EFFECTS. SAME TERRAIN EFFECTS AS 2-LANE ROADS IS ASSUMED. TABULATED FOR AADT FROM 0 TO 30000 VEH/DAY BY ACCESS DENSITY UNITS: ENCROACHMENT RATE: NUMBER OF ENCRO. PER MVMT (MILLION VEHICLES MILES TRAVELED) ENCROACHMENT FREQUENCY: NUMBER OF ENCROACHMENTS PER MI PER YR ACCESS DENSITY: NUMBER OF MAJOR ACCESS POINTS, INCLUDING ROADS & HIGHWAYS, PER MI (6 LEVELS: 0,1,2,3,4 & 5 ACCESS POINTS/MI) POSTED SPEED LIMIT: 65 MI/HR TERRAIN TYPE: FLAT BASELINE CONDITIONS: POSTED SPEED LIMIT=65 MPH, FLAT TERRAIN, RELATIVELY STRAIGHT SECTION, AND >= 12-FT LANE WIDTH. IMPORTANT NOTE: THESE TABLES CONTAIN ENCROACHMENTS ON RIGHT SIDE OF TRAVEL DIRECTION ONLY. MULTIPLY THESE NUMBERS BY A FACTOR OF 2 TO GET THE TOTAL IF LEFT SIDE IS ASSUMED TO HAVE THE SAME RATES. TABLE 1: BASELINE ENCROACHMENT RATES (ENC/MVMT) BY ACCESS DENSITY (ON RIGHT SIDE OF TRAVEL DIRECTION ONLY) ------------------------------------------------------ 65 MI/HR 65 MI/HR 65 MI/HR 65 MI/HR 65 MI/HR 65 MI/HR FLAT FLAT FLAT FLAT FLAT FLAT 0 PTS/MI 1 PTS/MI 2 PTS/MI 3 PTS/MI 4 PTS/MI 5 PTS/MI AADT ------------------------------------------------------ 0 | 0.58684 1.92419 3.82670 4.50192 4.79227 5.10134 1000 | 0.56383 1.84874 3.67666 4.32540 4.60436 4.90132 2000 | 0.54173 1.77625 3.53249 4.15579 4.42382 4.70913 3000 | 0.52048 1.70660 3.39398 3.99284 4.25036 4.52448 4000 | 0.50008 1.63968 3.26090 3.83628 4.08370 4.34708 5000 | 0.48047 1.57539 3.13304 3.68586 3.92358 4.17663 6000 | 0.46163 1.51362 3.01019 3.54133 3.76973 4.01286 7000 | 0.44353 1.45427 2.89216 3.40248 3.62192 3.85551 8000 | 0.42614 1.39725 2.77876 3.26906 3.47990 3.70433 9000 | 0.40943 1.34246 2.66980 3.14088 3.34345 3.55909 10000 | 0.39337 1.28982 2.56512 3.01773 3.21235 3.41953 12500 | 0.35594 1.16708 2.32101 2.73055 2.90666 3.09412 15000 | 0.32207 1.05602 2.10014 2.47071 2.63005 2.79968 20000 | 0.27999 0.91806 1.82577 2.14793 2.28646 2.43392 30000 | 0.24099 0.79018 1.57146 1.84874 1.96797 2.09490 ------------------------------------------------------ TABLE 2: BASELINE ENCROACHMENT FREQUENCIES (ENC/MI/YR) BY ACCESS DENSITY (ON RIGHT SIDE OF TRAVEL DIRECTION ONLY) ------------------------------------------------------ 65 MI/HR 65 MI/HR 65 MI/HR 65 MI/HR 65 MI/HR 65 MI/HR FLAT FLAT FLAT FLAT FLAT FLAT 0 PTS/MI 1 PTS/MI 2 PTS/MI 3 PTS/MI 4 PTS/MI 5 PTS/MI AADT ------------------------------------------------------ 0 | 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 1000 | 0.20580 0.67479 1.34198 1.57877 1.68059 1.78898 2000 | 0.39546 1.29666 2.57872 3.03373 3.22939 3.43767 3000 | 0.56993 1.86873 3.71641 4.37216 4.65414 4.95431 4000 | 0.73011 2.39394 4.76092 5.60097 5.96220 6.34673 5000 | 0.87685 2.87509 5.71780 6.72669 7.16053 7.62234 6000 | 1.01096 3.31483 6.59232 7.75552 8.25571 8.78816 7000 | 1.13321 3.71566 7.38947 8.69333 9.25400 9.85083 8000 | 1.24432 4.07996 8.11397 9.54567 10.16131 10.81666 9000 | 1.34497 4.40998 8.77029 10.31780 10.98324 11.69160 10000 | 1.43581 4.70785 9.36267 11.01470 11.72509 12.48129 12500 | 1.62397 5.32480 10.58962 12.45814 13.26162 14.11692 15000 | 1.76332 5.78169 11.49826 13.52711 14.39953 15.32822 20000 | 2.04394 6.70181 13.32815 15.67987 16.69114 17.76762 30000 | 2.63885 8.65245 17.20746 20.24369 21.54929 22.93910 ------------------------------------------------------ TABLE 3: LIST OF ADJUSTMENT FACTORS FOR POSTED SPEED LIMIT, TERRAIN AND NUMBER OF LANES (USE THESE FACTORS TO MULTIPLY THE VALUES IN TABLES 1 & 2 ABOVE) POSTED SPEED LIMIT =< 60 MPH: 1.121 POSTED SPEED LIMIT > 65 MPH: 1.000 TERRAIN = ROLLING: 1.735 TERRAIN = MOUNTAINOUS: 1.677 NUMBER OF LANES = 5: 0.980 NUMBER OF LANES >= 6: 0.962 Note: As some HSM and Washington State Cable Barrier data sets are being (or will be) analyzed, more, and perhaps better-estimated, adjustment factors will become available later.