APPENDIX I: ENCROACHMENT RATES, FREQUENCIES AND ADJUSTMENT FACTORS FOR TWO-LANE UNDIVIDED 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: TWO-LANE UNDIVIDED HIGHWAYS STATISTICAL MODELS: POISSON-GAMMA REGRESSION MODEL, ESTIMATED FROM THE COOPER DATA (575 ROAD SEGMENTS W/ MAX AADT < 13000 VEH/DAY) 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). TABULATION: FOR AADT FROM 0 TO 20000 VEH/DAY, BY ACCESS DENSITY, POSTED SPEED LIMITS & TERRAIN TYPE. CONSTANT EXTRAPOATION OF ENCRO RATE WAS MADE BEYOND AADT OF 15000 (AS SUGGESTED IN THE 4-LANE HWY ANALYSIS). TABULATED FOR AADT FROM 0 TO 20000 VEH/DAY BY ACCESS DENSITY. CONSTANT EXTRAPOATION OF ENCRO RATE WAS MADE BEYOND AADT OF 15000 (AS SUGGESTED IN THE 4-LANE HWY ANALYSIS). 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: 0,1,2,3,5 & 7 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 5 PTS/MI 7 PTS/MI AADT ------------------------------------------------------ 0 | 2.11489 10.21650 20.57350 31.86485 43.55409 46.94626 1000 | 1.52045 7.34488 14.79077 22.90840 31.31207 33.75078 2000 | 1.09308 5.28041 10.63344 16.46939 22.51099 24.26424 3000 | 0.82614 3.99085 8.03658 12.44730 17.01344 18.33852 4000 | 0.65639 3.17086 6.38533 9.88980 13.51775 14.57057 5000 | 0.52153 2.51936 5.07336 7.85778 10.74031 11.57680 6000 | 0.43999 2.12549 4.28022 6.62933 9.06122 9.76694 7000 | 0.37121 1.79320 3.61107 5.59293 7.64463 8.24003 8000 | 0.31950 1.54342 3.10807 4.81388 6.57979 7.09226 9000 | 0.28055 1.35527 2.72919 4.22705 5.77769 6.22768 10000 | 0.24635 1.19006 2.39649 3.71175 5.07336 5.46850 12500 | 0.17800 0.85985 1.73153 2.68184 3.66564 3.95114 15000 | 0.12861 0.62127 1.25108 1.93770 2.64853 2.85480 17500 | 0.12861 0.62127 1.25108 1.93770 2.64853 2.85480 20000 | 0.12861 0.62127 1.25108 1.93770 2.64853 2.85480 ------------------------------------------------------ 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 5 PTS/MI 7 PTS/MI AADT ------------------------------------------------------ 0 | 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 1000 | 0.55496 2.68088 5.39863 8.36157 11.42890 12.31904 2000 | 0.79795 3.85470 7.76241 12.02266 16.43302 17.71289 3000 | 0.90462 4.36998 8.80005 13.62979 18.62972 20.08067 4000 | 0.95833 4.62946 9.32259 14.43910 19.73591 21.27303 5000 | 0.95178 4.59783 9.25888 14.34044 19.60106 21.12767 6000 | 0.96358 4.65483 9.37367 14.51823 19.84407 21.38960 7000 | 0.94843 4.58163 9.22628 14.28994 19.53203 21.05327 8000 | 0.93294 4.50680 9.07558 14.05653 19.21300 20.70939 9000 | 0.92161 4.45207 8.96538 13.88585 18.97970 20.45792 10000 | 0.89918 4.34372 8.74717 13.54789 18.51777 19.96001 12500 | 0.81210 3.92307 7.90009 12.23590 16.72449 18.02706 15000 | 0.70412 3.40143 6.84964 10.60893 14.50068 15.63005 17500 | 0.82148 3.96833 7.99124 12.37708 16.91746 18.23506 20000 | 0.93883 4.53524 9.13285 14.14523 19.33424 20.84007 ------------------------------------------------------ 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: 1.330 POSTED SPEED LIMIT > 65 MPH: 1.000 TERRAIN = ROLLING: 1.735 TERRAIN = MOUNTAINOUS: 1.677 NUMBER OF LANES = 3: 0.829 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.