A review of design speed based on observed behaviour Zita Langenbach Arup Paul Lewis NUI Maynooth NUIM Research Team Tim McCarthy Lars Pforte Paul Lewis
What is Design Speed? The speed which determines the layout of a new road in plan, being the speed for which the road is designed, taking into account anticipated vehicle speed on the road (PIARC) A speed selected as a basis to establish appropriate geometric design elements for a particular section of road (TAC) The maximum safe speed that can be maintained over a specified section of highway when conditions are so favourable that the design features of the highway govern. (AASHTO) Design Speed
What is Operating Speed? The speed at which free-flowing vehicles choose to drive on a section of roadway (TRB) The highest overall speed at which a driver can travel on a given highway under favourable weather conditions and under prevailing traffic conditions without at any time exceeding the safe speed as determined by the design speed on a section-bysection basis. (AASHTO) Operating Speed
What is Design Consistency? The conformance of a highway s geometric and operational features with driver expectancy (Wooldridge et al. 2003) The road alignment shall be designed to ensure that standards of curvature, visibility, superelevation etc. are provided for a Design Speed which shall be consistent with the anticipated vehicle speeds on the road (NRA TA 85/13) Design Consistency
Current NRA TD 9 approach to Design Speed
Alignment Constraint Calculation, Ac For Single Carriageways Ac = 12 - VISI/60 + 2B/45 where: B = Bendiness degrees/km VISI = Harmonic Mean Visibility, m Alignment Constraint
Layout Constraint Calculation, Lc L Low Access 5 per km M Medium Access 6 to 8 per km H High Access 9 per km Layout Constraint
Selection of Design Speed Table 1/1 Selection of Design Speed (Rural Roads)
1 72 143 214 285 356 427 498 569 640 711 782 853 924 995 1066 1137 1208 1279 1350 1421 1492 1563 1634 1705 1776 1847 1918 1989 2060 2131 2202 2273 2344 2415 2486 2557 2628 2699 2770 2841 2912 2983 3054 3125 3196 3267 3338 3409 3480 3551 3622 Difficulty with current TD 9 approach N52 Mullingar to Delvin km/hr 120.0000000000 Poor correlation between computed & actual speed profiles 100.0000000000 80.0000000000 60.0000000000 40.0000000000 20.0000000000 0.0000000000 Distance at 5m sampling points Computed Design Speed (VTD9) Actual Average Velocity Current TD9 Approach
Contemporary Approaches to Design Speed Calculation in other Countries
Different Approaches to Design Speed Calculation Author Country Year Model Parameters Wooldridge et al USA 2003 V85 R, Fitzpatrick et al USA 2000 V85 R,K,G Krammes et. al USA 1998 V85 DC,LC,DF,L,VT TAC Canada 2013 V85 LC,R Dell Aqua et al. Italy 2012 V85 CP,Venv,CCR,LW, LT BAST Germany 1984 V85 CCR,LW Setra France 1986 V85 CCR Lamm et al. Greece 1995 V85 CCR McLean et al Australia 1979 V85 R, VF Different Approaches to Design Speed Calculation
Leisch and Leisch (1975) Operating-speed-based rural alignment consistency procedure 1. Within design speed, the potential average automobile speeds should not vary more than 16 km/h. 16 km/h (10mph) rule 2. When a reduction in design speed is necessary it should be no more than 16 km/h. 3. Average truck speeds should be no more than 16 km/h lower than average automobile speed. Leisch and Leisch (1975) Operating-speed-based rural alignment procedure
Further Operating Speed Models Lamm et al (1988) Refined German scheme applied in USA Rating D V85 Good D < 5º V85 < 10km/h Fair 5º < D < 10º 10km/h < V85 < 19km/h Poor D > 10º V85 > 19km/h Faghri et al (2004) Maximum 10km/h difference between two successive sections recommended Further Operating Speed Models
Canadian Operating Speed Approach (2007) Can alignment be modified? No Select Design Speed Select Design Parameters for Highway geometric Elements Yes Trial Alignment No Estimate 85th Percentile Speeds Satisfactory Alignment Final Design Yes Check consistency. Does estimated speed match design speeds Canadian (TAC) Operating Speed Approach (2007)
Operating Speed Model Austroads 2003 1. Length of Road to be analysed 2. Section Operating speeds Potential section operating speeds Section 1 Section 2 Section 3 S4 S5 S6 S7 Section 8 89km/h 93km/h 76 91 104km/h Operating Speed Model Austroads 2003
Operating Speed Model Austroads 2003 3. Acceleration on straights 4. Deceleration on curves Operating Speed Model Austroads 2003
Operating Speed Model Austroads 2003 5. Predicted operating speeds are finalised Operating Speed Model Austroads 2003
New Methodology For Design Speed Calculation Interim Results
Safe Profile Velocity (V sp ) Represents the average safe profile velocity of any route captured under ideal conditions: Good Weather & illumination Traffic free Alert driver, Low workload Safe but progressive driving (remain under posted speed limits) Over-taking not allowed V sp can be loosely compared with V 85 Safe Profile Velocity (V sp )
How to generate Safe Profile Velocity (V sp ) It is difficult to generate V sp for any route with a single pass since, in reality, we experience Slow vehicular traffic Other road users (pedestrians, cyclists, agriculture machinery) Traffic movement at Junctions, entrances Animals & Other transient events How to generate Safe Profile Velocity (V sp )
How to generate Safe Profile Velocity (V sp ) Drive 2 or 3 times Different drivers Different dates and times GPS trace of route Recording video can help significantly (e.g. Ubipix) Stack all GPS traces Compute maximum velocity (in this case at 5m) How to generate Safe Profile Velocity (Vsp)
Using Ubipix to acquire GPS encoded road video Support Multiple Mobile devices Cloud-based GeoMedia Platform GPS + Video Automated Upload & Publishing http://www.ubipix.com Using Ubipix to acquire GPS encoded road video
1 110 219 328 437 546 655 764 873 982 1091 1200 1309 1418 1527 1636 1745 1854 1963 2072 2181 2290 2399 2508 2617 2726 2835 2944 3053 3162 3271 3380 3489 3598 3707 3816 3925 4034 4143 4252 4361 4470 4579 4688 4797 4906 5015 5124 5233 5342 5451 5560 5669 5778 5887 5996 Ubipix used to capture V sp Passing-out cyclist 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 20.0000000000 0.0000000000 Ubipix used to capture V sp
1 116 231 346 461 576 691 806 921 1036 1151 1266 1381 1496 1611 1726 1841 1956 2071 2186 2301 2416 2531 2646 2761 2876 2991 3106 3221 3336 3451 3566 3681 3796 3911 4026 4141 4256 4371 4486 4601 4716 4831 4946 5061 5176 5291 5406 5521 5636 5751 5866 5981 6096 Ubipix used to capture V sp Slow Traffic in front 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 20.0000000000 0.0000000000 Ubipix used to capture V sp
How to generate Safe Profile Velocity (V sp ) N81 Blessington to Baltinglass Resulting V sp Driver-1 GPS stack of 3 X GPS Traces Driver-2 Driver-3 How to generate Safe Profile Velocity (V sp )
1 103 205 307 409 511 613 715 817 919 1021 1123 1225 1327 1429 1531 1633 1735 1837 1939 2041 2143 2245 2347 2449 2551 2653 2755 2857 2959 3061 3163 3265 3367 3469 3571 Existing design speed (V TD9 ) computation Shortcomings of current TD 9 Approach Existing (TD9) approach determines design speed v TD9 based on horizontal alignment, sight distance, entrances and road width on sections of at least 1 km length Even though it works well at high speeds, it misses local variability, since values above are averaged over the 1km section 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 20.0000000000 0.0000000000 v_td9 VSP Existing design speed (V TD9 ) computation N52 Mullingar-Delvin, v TD9 versus V sp
Enhanced theoretical design speed (V design ) computation using Sight Distance Background to an enhanced design speed (v design ) computation Sight distance is a critical component to safe driving A velocity is safe if the stopping distance is less-than or equal-to the sight distance so, we find velocity v max such that stopping distance equals sight distance, using the following formula: where s is sight distance in metres, d is deceleration in m/sec 2 and t is Reaction Time in seconds A deceleration of d=5 m/sec 2 and a reaction time of t=1.5 sec are used Enhanced v design =min(v TD9, v max ) Enhanced theoretical design speed (V design ) computation using Sight Distance
1 103 205 307 409 511 613 715 817 919 1021 1123 1225 1327 1429 1531 1633 1735 1837 1939 2041 2143 2245 2347 2449 2551 2653 2755 2857 2959 3061 3163 3265 3367 3469 3571 1 103 205 307 409 511 613 715 817 919 1021 1123 1225 1327 1429 1531 1633 1735 1837 1939 2041 2143 2245 2347 2449 2551 2653 2755 2857 2959 3061 3163 3265 3367 3469 3571 Enhanced theoretical design speed (V design ) computation using Sight Distance 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 20.0000000000 0.0000000000 v_td9 VSP N52 Mullingar-Delvin, V TD9 versus V sp Improved correlation 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 20.0000000000 0.0000000000 DESIGNSP VSP N52 Mullingar-Delvin, V design versus V sp Enhanced theoretical design speed (V design ) computation using Sight Distance
Research Test Routes N81 Brittas-Blessington-Baltinglass N52 Tyrrelspass-Mullingar-Delvin R406/405 Maynooth-Straffan-Kill National Routes reviewed
1 178 355 532 709 886 1063 1240 1417 1594 1771 1948 2125 2302 2479 2656 2833 3010 3187 3364 3541 3718 3895 4072 4249 4426 4603 4780 4957 5134 5311 5488 5665 5842 6019 1 170 339 508 677 846 1015 1184 1353 1522 1691 1860 2029 2198 2367 2536 2705 2874 3043 3212 3381 3550 3719 3888 4057 4226 4395 4564 4733 4902 5071 5240 5409 5578 5747 5916 Results N81 Blessington Baltinglass V sp versus V design 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 DESIGNSP VSP 20.0000000000 0.0000000000 Baltinglass - Blessington 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 DESIGNSP VSP 20.0000000000 0.0000000000 Blessington - Baltinglass Algorithm
1 84 167 250 333 416 499 582 665 748 831 914 997 1080 1163 1246 1329 1412 1495 1578 1661 1744 1827 1910 1993 2076 2159 2242 2325 2408 2491 2574 2657 2740 2823 2906 2989 3072 3155 3238 3321 3404 3487 3570 1 83 165 247 329 411 493 575 657 739 821 903 985 1067 1149 1231 1313 1395 1477 1559 1641 1723 1805 1887 1969 2051 2133 2215 2297 2379 2461 2543 2625 2707 2789 2871 2953 3035 3117 3199 3281 3363 3445 3527 Results N52 Delvin to Mullingar V sp versus V design 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 DESIGNSP VSP 20.0000000000 0.0000000000 Delvin - Mullingar 120.0000000000 100km/hr zone 100.0000000000 80.0000000000 60.0000000000 40.0000000000 DESIGNSP VSP 20.0000000000 0.0000000000 Mullingar - Delvin Algorithm
1 71 141 211 281 351 421 491 561 631 701 771 841 911 981 1051 1121 1191 1261 1331 1401 1471 1541 1611 1681 1751 1821 1891 1961 2031 2101 2171 2241 2311 2381 2451 2521 2591 2661 2731 2801 2871 2941 3011 1 68 135 202 269 336 403 470 537 604 671 738 805 872 939 1006 1073 1140 1207 1274 1341 1408 1475 1542 1609 1676 1743 1810 1877 1944 2011 2078 2145 2212 2279 2346 2413 2480 2547 2614 2681 2748 2815 Results Maynooth Kill (Naas) V sp versus V design 100.0000000000 90.0000000000 80.0000000000 70.0000000000 60.0000000000 50.0000000000 40.0000000000 30.0000000000 20.0000000000 10.0000000000 0.0000000000 Maynooth - Kill DESIGNSP VSP 120.0000000000 Straffan Village 100.0000000000 80.0000000000 60.0000000000 40.0000000000 DESIGNSP VSP 20.0000000000 0.0000000000 Kill - Maynooth Algorithm
1 96 191 286 381 476 571 666 761 856 951 1046 1141 1236 1331 1426 1521 1616 1711 1806 1901 1996 2091 2186 2281 2376 2471 2566 2661 2756 2851 2946 3041 3136 3231 3326 Results N52 Tyrellspass to Mullingar V sp versus V design 120.0000000000 100.0000000000 80.0000000000 60.0000000000 40.0000000000 DESIGNSP VSP 20.0000000000 0.0000000000 Algorithm
Consistency Measured using severe Deceleration Delvin to Mullingar Acceleration derived from V sp profile Define a deceleration threshold value of say, -1.5m/sec 2 These zones require closer examination Consistency Measured using severe Deceleration
Summary NRA initiated a research project to develop a new approach to computing Design Speed along National Roadways Developing a methodology for collecting and processing safe profile velocity (V sp ). Need to ensure robust minimum sample size Devising a more comprehensive theoretical approach to computing Design Speed based on Sight Distance. This needs to be enhanced to take into account vertical alignment, width, entrances etc. Examining Design Consistency along route using deceleration derived from V sp. Need to extend this to include road geometric elements, sight distance etc Can now begin to compare all of the above dynamic & static information to get a better understanding of the safety performance of road networks Summary
Thank You Any Questions